XEphem
pronounced eks i
fem´
Version 3.7.7
Reference
Manual
© 1990-2015 Elwood Charles Downey
1 Introduction
XEphem is a scientific-grade interactive astronomical ephemeris
package. XEphem:
- computes heliocentric,
geocentric and topocentric information for all objects;
- has built-in support for all planets;
the moons of Mars, Jupiter, Saturn, Uranus and Earth; central
meridian longitude of Mars and Jupiter; Saturn's rings; and Jupiter's Great Red Spot;
- allows user-defined objects
including stars, deepsky objects, asteroids, comets and Earth
satellites.
- provides special efficient handling of large catalogs including Tycho,
Hipparcos, GSC.
- displays data in configurable
tabular formats in conjunction with several interactive
graphical views;
- displays a night-at-a-glance
24 hour graphic showing when any selected objects are up;
- displays 3-D stereo Solar
System views that are particularly well suited for visualizing
comet trajectories;
- quickly finds all close pairs
of objects in the sky;
- sorts and prints all catalogs with very flexible criteria for
creating custom observing lists;
- creates plots of any pairs
of all data fields throughout the program;
- downloads current asteroid and
comets ephemerides from Lowell Observatory and Minor Planet
Center;
- downloads timely Earth satellite
orbital TLE parameters;
- plots true binary system orbits;
- downloads Digitized Sky Survey
FITS files from STScI or ESO;
- provides a handy coordinates
spreadsheet for converting
among
equatorial, ecliptic, horizon and galactic frames ;
- displays live SOHO images of the Sun;
- includes a compiler for entering and solving user-written functions using
any data fields;
- serves as the control point for GOTO
telescopes such as Meade LX200 or other external applications;
- displays FITS files images
overlaid with database symbols and other graphical information;
- performs automatic star pattern matching to automatically solve for World Coordinate
System on any image;
- performs 1-click 2D Gaussian relative and absolute photometry;
- defines and saves any number of Eyepieces
to use in sky maps;
- captures, displays and clips to any number of local horizon profiles;
- stores sets of all Sky View options in history sets for easy playback later;
- prints using high quality Postscript;
- allows you to assign any number of objects as Favorites for special fast access
throughout the program, and makes them available even when their
original databases are no longer loaded;
- provides an extensible image
gallery initialized with over 300 beautiful and informative
color images of deep sky objects;
- provides an observing logbook
which is automatically filled in with observing circumstances, with
searching on most fields;
- displays magnetic deviation
for any location.
- create movie loops of any View, NAAG or Plot window.
XEphem can compute information on demand or time can be set to
increment automatically. In this way a series of computations and
movies can be generated.
1.1 Quantitative
information
Quantitative information available about each object includes:
- RA and Dec,
- local azimuth and altitude,
- distance from sun and earth,
- light travel times,
- heliocentric coordinates,
- galactic coordinates,
- ecliptic coordinates,
- solar elongation,
- angular size,
- visual magnitude,
- illumination percentage,
- local rise and set times and azimuths,
- local transit times and altitude,
- length of time up,
- constellation,
- angular separations between all Favorites.
1.2 Local circumstances
Local observing circumstance information includes
- UTC and local date and time,
- local sidereal time,
- times astronomical, nautical and civil twilight and length of
night,
- local temperature and pressure (for refraction),
- elevation above sea level (for parallax),
- a monthly calendar.
Equatorial coordinates may be computed in any four combinations of
topocentric or geocentric, and apparent or astrometric. When the
Equinox is set to a fixed date the values are astrometric, that is,
corrected only for precession and light travel time. When the Equinox
is set for EOD (Equinox of Date) the values are apparent and are also
corrected for nutation, aberration and relativistic deflection.
Topocentric values are further corrected for parallax, augmentation
and refraction.
1.3 Launching XEphem
In addition to all the standard X Window System command line arguments,
XEphem also supports the following command line arguments:
Argument
|
Meaning
|
-env name=value
|
set internal value for
environment variable; any number allowed
|
-help
|
print this then exit
|
-install {yes no guess}
|
whether to install a private
colormap, default is guess
|
-log
|
save exit trouble to private log
|
-nosplash
|
disable splash screen from now on
|
-nowin
|
do not restore windows
|
-prfb
|
print all internal default
resources then exit
|
-resfile f
|
load alternate X resource file
|
-splash
|
show splash screen from now on
|
1.3.1 Shared and Private Directories
When XEphem is launched it looks for a file named .xephemrc in the user's $HOME directory. This file is
optional. If it exists, it should contain a line with the following
form:
XEphem.PrivateDir:
~/.xephem
The directory named on the right is where XEphem will create and look
for Private files, so-called
because on a multiuser system they are expected to be separated on a
per-user basis. A leading "~" in the file name can be used to refer to $HOME, your login directory.
A leading "." in the file name can be used to refer to the current
working directory of the running program. The example above causes the
Private directory to be .xephem
in the users $HOME
directory. If .xephemrc
does not exist or does not contain this line the default Private
directory is ~/.xephem.
The private directory will be created if it does not already exist.
XEphem then also searches for another directory for Shared
files. This directory contains files presumed to be shared
among all XEphem users on a system. Files in this directory are never
modified by XEphem. They include databases of objects, supporting
images and other files. This directory is specified in a resource file
named XEphem which may be
located in any of the standard X Window System directories, in
/etc or within the Private directory (see above). It should contain a
line with the following form:
XEphem.ShareDir:
/usr/local/xephem
Next, XEphem sets the initial values of most options and settings from
other entries in the resource file. Settings which do not appear will
use their internal default values. Internal defaults may be printed
using the -prfb command line option.
1.3.2 Main window control
XEphem starts by showing the Main window with each parameter set to
its default value. The parameters on the Main window are primarily
devoted to describing the location and time for which all other data
in XEphem are computed.
Most fields on the Main window may be changed by clicking them. A
prompt window with a brief explanation of the field will appear. A new
value may be typed into the text field provided. If Ok is clicked the new value will be
used; if Cancel is clicked the
field will be left unchanged. In either case, the prompt window goes
away. Some of the windows have an extra button which offers a handy
way to enter frequently used values for the field.
If you change a field on the Main window that would invalidate any of
the other fields in any XEphem window the message NEW CIRCUMSTANCES
flashes near the top of the Main window. This will continue until the
next Update occurs. If you change any field that causes new
circumstances, the Step value is not added to the current time before
the next loop.
You can change time manually like any other fields or you can set up
looping to advance time automatically with specified pauses between
each step. The prominent button at the bottom of the Main window
labeled Update causes all
other
windows throughout XEphem will be recomputed with the new time.
Looping effectively presses this button for you. See Looping.
Some graphical views have a push button marked Movie Demo. This is a convenient way
to start and stop a sample movie sequence. If XEphem is currently idle
then pushing the button will set the Main window Step size to a value
that will yield a pleasing motion effect and start looping with a very
large number of steps. If XEphem is already looping then pushing the
button will cause it to stop and set Main window N Steps to 1. The
Main window Stop control can also stop the looping in the usual way.
1.4 Time
and angle formats
Time and RA are displayed as h:m:s. They may be entered the same way
or the color (:) may be entered as slash (/) semicolor (;) comma (,)
or space. Other angular quantities, such as declination, azimuth,
altitude, longitude and latitude, are entered and displayed as d:m:s
but
otherwise use the same rules.
Components of a sexagesimal field may be entered as floating point
numbers. For example 10:20:30 may also be entered as either 10:20.5 or
10.34167.
Negative values are indicated by one hyphen (-) before the first
character.
Dates are entered and displayed in any one of the forms month/day/year,
year/month/day or day/month/year, depending on the Preferences selection on the Main
menubar. The slash (/) may also be entered as hyphen (-) semicolon (;)
or comma (,). Note you must always enter the full year.
When the day portion of a date is an integer, the time does not change.
When the day portion of a date is entered as a floating point number,
the time will also change to correspond to the fractional portion of
the day. For example, using the preference m/d/y, entering a date of
1/1.5/1995 will set the date to 1/1/1995 and the time to 12:00:00. To
get this effect with a whole day, include the decimal point. For
example, 1/1.0/2002 will set the date to 1/1/2002 and the time to
0:00:00.
You may also enter a date as a decimal year, as in 1990.12345.
Negative years indicate BC dates. For example, Jan 1, 1 BC is given
as 1/1/-1. Before you ask, yes, "1-1--1" works for 1 BC. There is no
year 0.
2.0 Main
Window
XEphem's
main window is divided into five regions plus the menu bar across the
top for selecting the principle functions of XEphem. Each window
opened from the menu bar has its own Help.
Beneath the XEphem logo image is a status line that contains a short
description of what XEphem is doing at the moment with regards to its
looping behavior.
Below the status line is room for the NEW CIRCUMSTANCES message. When
you change any field on the Main window that could invalidate any of
the other fields or views throughout XEphem this message flashes until
at least one screen Update occurs to get everything up to date again.
2.1 Main's Help menu
XEphem help is written in html version 4.01 transitional and requires a
browser
to read. The text is all in one file, xephem.html, located in
auxil/help within the Shared directory path. Anchors throughout the
file
allow XEphem to specify exactly where to jump for each Help entry.
Help » Configure
This Help entry is used to set how
XEphem sends a URL to your
browser. It must be correct before any other Help can be used. It
displays a table showing sample
shell commands that accomplish this for several popular browsers
including mozilla, netscape, opera, konqueror and safari. Each time %s
appears in the definition the full path to the xephem.html will be
substituted. If you figure
out how to configure for another browser or you know of a better
definition please send us your results and we will post on our web site.
Note the entry for using IE under
cygwin. In order for this to work,
you must create an
environment variable before running XEphem named XEHELPURL set to the
full Windows path of the xephem.html file using Windows filespec
notation. The value of this variable is substituted for each %s
appearing in the definition for IE.
Help » on Context
This Help entry turns the cursor into a
Question Mark. Roaming the cursor over any
control in XEphem will show its bubble help tip whether or not the tips
Preference is active. Press the
left
mouse button to end this behavior and resume normal operation.
All remaining Help entries just bring up additional information as one
would expect. If you are new to XEphem, we suggest you begin by reading
the next three entries in order, Introduction, Operation and Triad
formats, then feel free to explore.
2.2 Menu bar
2.2.1 File
- System log... displays a
scrolled list of informational messages and alert. XEphem may beep
whenever a new message is added, depending on the Log Bell preference. See System
log.
- Gallery... displays a
list of installed color images and allows browsing or marking in Sky
View. See Gallery.
- Network setup... displays a window offering choices for
how XEphem accesses the
Internet. See Internet.
- External file... drives XEphem from a file containing
times and latitude/longitude locations.
See External input.
- Progress Meter... displays a simple bar graph of XEphem
progress. The accuracy and usefulness
of the display are somewhat problematic at this time.
- Forward 1 Step causes Time to be changed by one Step
value. This action can also be performed when the cursor is over any
XEphem window by typing Control-f. Invoking this command also stops
looping if it is running.
- Backward 1 Step causes Time to be changed by the negative
of one Step value. This action can also be performed when the cursor
is over any XEphem window by typing Control-b. Invoking this command
also stops looping if it is running.
- Update performs the same action as the Update
button across the bottom of the Main window. This can also be performed
by typing Control-u in any XEphem window. See Looping.
- Quit... exits XEphem. If any resources have been modified
and Preferences »
Confirmations is On, a reminder will first appear and allow
you to bring up the Save window if desired. This can also be
performed by typing Control-d in any XEphem window.
2.2.2 View
The View menu gives access to all of the several XEphem
specialized displays.
- Data Table... highly
configurable, show any from a selection of over 30 parameters for
each Favorite object. See Favorites and Data table.
- Sun... show SOHO images
of
the Sun, measure current RA and Dec of solar features. See Sun.
- Moon... show real lunar
image, mark hundreds of natural and artificial features, compute sun
and
observing circumstances. See Moon.
- Earth... show spherical
or
cylindrical projection, satellite ground tracks. See Earth.
- Jupiter... show planet
image with moons and shadows. See Jupiter.
- Saturn... show planet
image with moons and shadows. See Saturn.
- Uranus... show planet
symbol with moons. See Uranus.
- Sky View... the showpiece
of XEphem, display maps, images, trails. See Sky
View.
- Solar System... 3D and
perspective diagrams include asteroids, comet trajectories. See Solar System.
2.2.3 Tools
The Tools menu gives access to windows allowing full control
of the following functions:
- Plot values... plot pairs
of any data values shown throughout XEphem. See Plotting.
- List values... print
columnar lists of any data values shown throughout XEphem. See Listing
- Solve equation... define
and solve any mathematical function using any data values shown
throughout XEphem. See Solver.
- Find close pairs... search all loaded database objects and
sort all pairs by increasing separation. See Close
pairs.
- Night at a glance... display when all Favorite objects are
up over a 24 hour period. See Night at a
Glance.
- Coordinates converter...
enter one of equatorial, horizon, ecliptic or galactic coordinates
and show the others. See Coordinate converter.
- Observers log book...
click on a target in Sky View to fill in standard observing fields,
add your own notes and save, later browse or search for entries. See Observers logbook.
2.2.4 Data
The Data menu gives access to windows which pertain to
managing the objects in memory.
- Files... adds and deletes
catalogs of objects to and from memory. The window also displays
overall
statistics of the number of each type of object in memory. See Data Files.
- Index... searches and
displays all information about any given object in memory. Also can
be used to center the Sky View over any object. See Data
Index.
- Favorites... adds,
enables, sorts and deletes the set of objects you wish to have easy
access to. See Favorites.
- Internet... provides a
convenient means to update XEphem databases from the Net. The window
comes preconfigured to get timely asteroid, comet and Earth
satellite catalogs. See Internet.
- Field stars... sets up
how and whether to read several very large databases of faint stars
which XEphem refers to as "field stars See Field
stars.
2.2.5 Preferences
The Preferences pulldown lists the available preferences that may be
changed at run time. Whenever any are changed, all effected fields are
immediately recalculated and redisplayed throughout XEphem. The simple
preferences include:
- Equatorial: Topocentric,
Geocentric. controls whether the RA and Dec values displayed
throughout XEphem are for the current local surface location
(topocentric) or from the center of the Earth. (Alt/Az values are,
of course, always topocentric.)
- Precision: Hi, Low
controls how much precision is shown for most angles. This is a change
in display format only and does not imply a change in accuracy.
- Log Bell: On, Off whether
to ring the bell each time a new message is added to the System log
window. The System log window is accessible via the File menu in the
Main menu bar. See System log.
- Prompt Prefill: Yes, No
whether prompt strings from the Main window and Search windows are
filled with the current value or blanked out. This is also handy to
allow copy/paste of these values.
- Units: English, Metric
whether local topocentric circumstances are given in English or
Metric units of measure.
- Time zone: UTC, Local
whether the time stamp below each major view, the rise/transit/set
times in the Data Table window and the dawn/dusk times and the
calendar in the Main window refer to UTC or local time.
- Show help tips: Yes, No
whether additional help is available immediately for all selectable
buttons and controls using small brief windows near the control.
- Confirmations: Yes, No
whether operations which basically can not be undone or which might
have irreversible consequences will be preceded with a confirmation
window. Examples include exiting XEphem or overwriting an existing
file.
- Start week on: Saturday, Sunday,
Monday sets the day on which weeks begin in the Main calendar.
- Date formats: M/D/Y, Y/M/D,
D/M/Y whether dates are shown and entered in month/day/year,
year/month/day or day/month/year format.
- Fonts... displays a
window
to experiment with fonts while you watch. See fonts.
- Colors... displays a
window to experiment with colors while you watch. See colors.
- Save... displays a window
which shows how the current functional settings differ from their
defaults and allows them to be saved. See save.
2.3 Sections
The Main window is divided into five basic sections.
2.3.1 Local
- [Site name] Above the
Latitude field is a button which can display the current site name.
Pressing this button will bring up a list of cities and
observatories. See Sites.
- Latitude Local geographic
latitude, positive degrees north of equator. Changing this will
disable automatic computation of Daylight Savings Time.
- Longitude Local
longitude,
positive degrees west of Greenwich meridian. Changing this will
disable automatic computation of Daylight Savings Time. A sensible
Timezone is created based on one hour for each 15 degrees from 0.
- Elevation Local elevation
of the ground above sea level, in feet or meters. (see
implementation notes). Used in topocentric parallax correction.
- Temp Local surface air
temperature, in °F or C. Used in refraction correction.
- Atm Pres Local surface
air pressure, in inches of mercury or hPa. Used in refraction
correction.
- Equinox When set to a
year, this is the desired epoch to which the RA/Dec fields are
precessed, referred to as the astrometric place. When this is set to
EOD, all RA/Dec values are precessed to the current XEphem time, and
corrected for nutation, aberration and deflection, referred to as
the apparent place.
- Mag decl This is the
amount by which the horizontal component of the Earth's magnetic
field varies from true north. Put another way,true az = magnetic
bearing - mag decl. The model is stored in the file wmm.cof in the
auxil directory of the shared directory. It is valid for 2000
through the end of 2004. Check http://www.ngdc.noaa.gov/seg/potfld/DoDWMM.shtml
for updates.
<IP_ADDRESS> Site Selection
This
window allows you to search, load and add to a collection of predefined
sites.
The scrolled list at the top lists the complete set of currently
defined sites. Clicking on one will copy it to the Set text field. Double clicking on
one will also install it to the Main window, as will clicking on Set
or typing Enter over the select text field.
To search for a particular site, either scroll through the list or
type a glob pattern in the Search text field. Clicking on
Search or typing Enter in the search text field will scroll the list to
the
next site that matches the search text.
Creating new sites.
Clicking Create expands the
dialog to add fields for creating new sites. Fill in the fields then
click Set main to test the
entry and Save to add it to
the
collection on disk.
File format:
XEphem stores sites in the file named xephem_sites. One may
reside in
either or both the Shared and Private
directories. The Sites window always checks both.
Each line in the file consists of 5 fields, each separated by a
semicolon (;):
Name ; Latitude ; Longitude ;
Elevation ; Timezone
where:
Name
is the City, State, Country or other designation, up to 40
characters.
Latitude
is DD MM SS, followed by an N or S to indicate north or south of the
equator. Each portion is separated by a blank.
Longitude
is in DDD MM SS, followed by an E or W to indicate east or west of
the prime meridian in Greenwich, England. Each portion is separated
by a blank.
Elevation
is in meters. If you do not know your elevation, put "-1.0".
Timezone
indicates the offset from GMT and details of savings time formatted
as follows:
std
offset dst [offset],start[/time],end[/time]
There are no spaces in the
specification. All fields except the initial
std
string are optional. It specifies the name of the standard time zone
and must
be three or more alphabetic characters.
The
offset
string indicates the value added to the local time to arrive at
Coordinated
Universal Time. The offset has the format
hh[:mm[:ss]].
The minutes (mm) and seconds (ss) are optional. If preceded by a minus
(-) the timezone shall be east of the Prime Meridian;
otherwise, it shall be west (which may be indicated by an optional
preceding
plus (+)).
The dst string and second offset specify the name and
difference between the daylight savings time zone and the standard
time zone. If the offset is omitted, it defaults to one hour ahead
of standard time.
The start field specifies when
daylight savings time goes into effect and the end field specifies when the
change is made back to standard time. These fields have the
format Mm.w.d which
specifies day d (0 <= d <= 6) of week w (1 <= w <= 5) in
month m (1 <= m <= 12). Day 0 is Sunday. Week 1 is the
first week in which day d occurs and week 5 is the last week in
which day d occurs. If omitted, Savings time will begin the first
Sunday in April and end the last Sunday of October.
The time fields specify when, in
the local time currently in effect, the change to the other time
occurs. If omitted, the default is 2:00:00.
Here are a few examples:
Munich, Germany
; 48 14 0 N ; 11 57 0 E ; 523 ;
MET-1METDST,M3.5.0,M10.5.0
New York, New York ; 40 45 6 N
; 73 59 39 W ; 16.8 ; EST5EDT
Sydney, Australia ; 33 52
0 S ; 151 12 0 E ; 7.6 ; EST-10EST,M10.5.0,M3.5.0
Lines in the file which do not conform to this structure are ignored.
2.3.2 Time
- Julian Number of days
since noon 4713 BC to about 1-second accuracy. Used as a uniform
time scale.
- UTC Date The UTC date.
UTC is Universal Coordinated Time, the basis,after adjusting for
time zones, for the official "civil" time people set their clocks
to. Every year or so it is adjusted via a leap second so it stays
within 0.9 seconds of UT1, which varies continuously with the slight
irregularities of the rotational motion of the Earth.
- Sidereal The apparent
sidereal time for the current time and location. Equals the apparent
RA at the local meridian.
- TZ Name The local time
zone name. The name may be fixed to any short mnemonic. Setting this
manually turns off automatic computation of Daylight Savings Time.
When auto DST is on, a small clock is shown at the top right of the
Time section.
- TZ Offset Hours local
time is behind UTC, i.e., positive west or negative east of
Greenwich. Setting this manually turns off automatic computation of
Daylight Savings Time.
- Local Date The local
date. This is UTC date minus the value of TZ Offset.
- Local Time The local
time. This is UTC time minus the value of TZ Offset.
- Delta T TT-UT1. Number
of seconds by which Terrestrial Time (aka Ephemeris Time prior to
1982) leads UT1. TT is generally of interest when calculating the
positions of solar system objects because it is a continuous time
scale unaffected by the Earth's rotational vagaries. The term
Terrestrial means it is adjusted for the relativistic effects of
gravity and the Earth's revolution around the Sun. UT1 or UTC is of
interest when relating those positions to the horizon to produce
altitudes and azimuths. The value may be computed automatically
based on the current time or entered manually (in which case it will
not change). The algorithm uses values tabulated in the Astronomical
Almanac for years 1620.0 through 1998.0, and is accurate to within a
few seconds over that interval. Dates prior are from Stephenson and
Morrison or K. M. Borkowski, with an estimated error of 15 minutes at
1500 B.C. A linear extrapolation formula predicts future values.
2.3.3 Calendar
The
calendar on the right of the Main window is based on local time or
UTC, depending upon the Time Zone preference. Clicking a date button
will set the date. Clicking dates before the first of the month and
after the last of the month will also change month or year as
necessary. The month and year buttons pop up menus that allow these to
be changed as well. At the bottom the Now
button sets the time and date to the computer clock. The arrow buttons
move backwards or forwards by one day or week. Except for Now, using
the
calendar does not change the current time, just the date.
New and Full Moons are marked on the day on which they occur in
the selected time zone.
2.3.4 Night
- Sun icon When the sun
is above the local horizon a small sun symbol is drawn in the upper
left corner of this section.
- Moon icon When the moon
is
above the local horizon a small symbol is drawn in the upper right
corner of this section depicting the approximate phase of the moon.
The brighter of the foreground and background colors is used to draw
the portion in sun light.
- Sun Dip The number of
degrees the Sun is below the horizon that we wish to call twilight.
Common definitions include:
- Civil = Sun 6 degrees down (can just tell whether headlights
are on),
- Nautical = Sun is 12 degrees down (sky and ocean merge),
- Astronomical = Sun is 18 degrees down (dark as it gets).
The Sun Dip setting applies to the
following fields:
- Dawn Local or UTC time
when the Sun center is Sun dip degrees below the horizon before sunrise
today.
- Dusk Local or UTC time
when the Sun center is Sun dip degrees below the horizon after sunset
today.
- Length Length of
astronomical night, i.e., Dawn - Dusk. If this and the display for
Dawn and Dusk are shown as "-----", it means the Sun is either
always below or always above Sun dip degrees below the horizon on
this particular day.
N.B. These three fields always apply to the local current day.
Difficulties arise when these events occur within 4 minutes of local
midnight with respect to the time zone defined by TZ Offset. In
particular, if these fields are not behaving as you would expect,
check that the TZ Offset is set commensurate with the current
Longitude.
- LST@0 Local Sidereal
Time at next local Midnight, as per the time zone.
2.3.5 Looping
- -1 +1 These are shortcuts to go
backwards or forwards by one Step. Can also be performed by typing
Control-b and Control-f from any window.
- RT Clicking this
button will synchronize XEphem to the computer clock and commence
Updating every Pause seconds. If Pause is 0 when this is started, it
will be set to 10 seconds. This can be the initial mode for XEphem by
saving the AutoRT Preference.
RT is really just a shortcut for:
- clicking Now under the calendar
- setting Step to Clock
- setting N Steps to something large and then
- clicking Update.
- Step The interval by
which, or event to which, time is changed each loop. Fixed intervals
are
specified in hours, minutes, seconds, days and years or time may be set
to advance to an event such as the next sun rise, dawn or full moon.
- N Steps The number of
times the display will be updated (time advanced by Step each step)
automatically. When Update is clicked, this number counts down until it
reaches zero then is reset to one.
- Pause Number of seconds
to
pause between screen Updates. This is used mainly to set up for
free-running unattended operation. Pausing is not done when plotting,listing or solving are active. When looping, time is
maintained at a whole multiple of pause length.
When looping is in effect, the label on the bottom button changes to Stop. When the number of steps
goes to 0 or the Stop button is clicked the looping stops and the
button label changes back to Update.
Note that when looping with Pause set to 0, most graphics and numeric
field data are not drawn in order to speed up the computations. These
values are always updated internally, however. and may safely be used
for plotting,listing and solving. This is true even if the window that
displays the information is closed.
3.0 File menu
3.1 System log
This window contains additional
information from XEphem. Whenever an entry is written the computer may
beep, depending on the setting of the Log
bell Preference. The
contents of all Alert windows are also written here. Scroll bars to the
right and below allow panning through the log.
Erase
Permanently discards all log entries.
Close
Closes the log window but has no
effect
on its contents or ability to capture further information.
3.2 Gallery
This window is a portal to high quality
color images.
The Gallery window is broken into three sections. Down the right side
is a scrolled list of the
available images. Images are displayed in the upper left, captions in
the lower left. All sections scroll
to accommodate large areas. A sash between the upper and lower
sections on the left allow you to control the proportion of vertical
space used by each.
Controls across the bottom:
Close
Close the Gallery window.
Rescan
Reinitialize the list. This also occurs each time the
Gallery window is opened.
Sky Point
If the current XEphem database contains an object whose
name matches the Gallery object currently being displayed, this button
will
be active and clicking this button will center the object in the Sky
View.
3.2.1 File format
The Gallery database index is stored in one or more files with the
suffix .gly. The index files and the image files to which they
refer reside in a directory named gallery which in turn must
reside within either the Shared or Private
directories. All index files found are combined and sorted by name into
the scrolled list.
The index file is in XML format. The entire collection is within one
outer-most element named gallery. In turn it contains one
element named image for each
Gallery image file.
In turn it contains one or more elements named name, one
element named file and one element named description.
The file name is with respect to the directory in which the .gly file
resides. When XEphem reads the description contents, it replaces
isolated newlines with blanks so that word wrapping is left up to the
scrolled text window. Please refer to the following example.
<gallery>
<image>
<name>
NGC 4414
</name>
<file>
1999-25-a-web_print.jpg
</file>
<description>
In 1995, the majestic spiral galaxy NGC 4414 was imaged by the Hubble
Space Telescope as part of the HST Key Project on the Extragalactic
Distance Scale. An international team of astronomers, led by Dr. Wendy
Freedman of the Observatories of the Carnegie Institution of Washington,
observed this galaxy on 13 different occasions over the course of
two months.
Image Credit: Hubble Heritage Team (AURA/STScI/NASA)
</description>
</image>
</gallery>
3.3 Network
Setup
This
window controls how XEphem tries to
connect to
the Internet. One of the following three choices must be turned on for
Internet access to be available.
- Direct connect This
choice
just means to use the direct DNS/IP TCP/IP sockets as necessary. Use
this one unless you are behind a firewall.
- via Proxy This choice
attempts to access the Internet via a Proxy. Type the port address
and the host name of the proxy in the fields provided.
- via SOCKS This choice
attempts to access the Internet via a version 4 SOCKS server. Type
the port address and the host name of the server in the fields
provided. These values can be initialized using the environment
variables SOCKS_PORT and SOCKS_NS.
If your Proxy or SOCKS firewall require Authentication, turn on the Auth option and enter name and
password in the fields provided. Note that only the Name field may be
Saved.
3.4 External Input
XEphem
can read a file (or fifo)
containing sets of
time, latitude and longitude values and automatically install these
values sequentially unattended. Enter the name of the file in the
window
and press OK. To pause between updates, set the desired delay in the
Pause field of the Main window. All features of XEphem, such as plotting and listing are
available while this feature is running.
The format of each line of the file is as follows:
JD
Lat Long
where
JD = Julian Date
Lat = Latitude, radians, +north
Long = Longitude, radians, +west
The fields are separated by one or more blanks or tabs. All lines not
having exactly three floating point values are ignored and may be used
for comments, etc.
4.0 View menu
4.1 Data Table
This is a table of information about each of the current
Favorites. Each data item occupies one
column in the table and each object occupies one row.
The Control pulldown menu contains the following options:
- Setup... This button
brings up a configure window to specify the table rows and columns
as desired.
- List... This button
allows the current data table to be saved in a text file.
- X Select
This button puts the current contents of the data table into the X11
PRIMARY selection buffer. You can then typically paste it into a file
using the middle mouse button.
When any columns related to rising or setting are active a box at the
bottom will indicate whether the times refer to the center or the
upper limb of the object. Similarly, when either the RA or Dec columns
are active or any of the separation columns are active a box will be
present to indicate whether the separation is from a geocentric or
topocentric point of view. The box will also indicate the precession
epoch.
Any of the information in this table may be plotted,
listed or used in a solver
algorithm.
4.1.1 Data setup
This
window lets you configure which columns will be in the Data Table.
When this window first comes up it will be set to indicate the state
of the Data Table. You may then manipulate the toggle buttons as
desired. To actually change the Data Table to a new configuration
select the Apply button. Ok does the same thing but also
closes this window. Close just
closes this window without making any permanent changes.
Entries are grouped into three sections for clarity. Column one
controls miscellaneous basic information. The descriptions of each
entry are as follows:
- Cns name of the
constellation in which the object appears.
- RA Right ascension: if
Main Equinox is set to EOD this is the apparent place, otherwise it
is the astrometric (mean) place. If Main Preference Equatorial is
Topocentric, it is further corrected for parallax.
- HA geocentric or
topocentric hour angle of object, computed as LST-RA precessed to
EOD. Positive angles are west of the meridian.
- GHA Greenwich Hour Angle,
hour angle of object when at 0° longitude.
- Dec Declination: if Main
Equinox is set to EOD this is the apparent place, otherwise it is
the astrometric (mean) place. If Main Preference Equatorial is
Topocentric, it is further corrected for parallax.
- Az topocentric degrees
eastward of true north for object.
- Alt topocentric degrees up from a
horizontal plane that is Elevation feet above sea level. Corrected
for refraction.
- Zenith topocentric Zenith
distance, degrees; corrected for refraction.
- PA parallactic angle, i.e., the angle as seen from the
target between zenith and NCP, measured positive westward of meridian.
- JD current UTC Julian date.
- HJD current heliocentric Julian date, i.e., JD adjusted to
time frame of Sun.
- Air Number of relative
air masses through which light from the object passes to the
topocentric observer. Computed by the method of Hardie, clamped to a
max at 3 degrees altitude.
- VMag visual magnitude
of object.
- PMRA Proper Motion in RA. Units are arcseconds/hour for a
Solar system object, degrees/minute for an Earth satellite and
milliarcseconds/year for all other types of objects.
- PMDec Proper Motoin in Declination. See PMRA for units.
- Size angular size of
object, in arc seconds. If not otherwise given, estimated for
objects in heliocentric orbits from the absolute magnitude parameter H
and by assuming an albedo of 0.10, for which H is 18 for an object
of 1.06 km diameter at 1.0 AU.
- Phase percent of visible
surface in sun light.
- Elong spherical angular
separation between the Sun and given object, calculated from the their
geocentric ecliptic coordinates. Note this is not just the
difference in ecliptic longitude, as is sometimes used. The sign is
positive for an evening object or negative for a morning object.
Thus, this field is not generally useful in searching for eclipses
because of the discontinuous sign change which occurs at
conjunction. For that, use the individual Separations fields.
- Spect Basic spectral
classification, if appropriate.
- HeLat true heliocentric
latitude, in degrees. For the Moon this is the geocentric latitude.
- HeLong true heliocentric
longitude, in degrees. Earth's is displayed on the Sun's line. For the
Moon this is the geocentric longitude.
- GLat galactic latitude,
in
degrees. Based on 32.93192° longitude of ascending node on
equator, 192.85948° RA J2000 of North Galactic Pole and
27.12825° Declination of pole.
- GLong galactic longitude,
in degrees. See GLat for definition.
- EcLat ecliptic latitude,
in degrees.
- EcLong ecliptic
longitude,
in degrees.
- EaDst true distance from
Earth center to object center, in AU, except distance to the Moon is
in miles or km depending on the Units preference.
- EaLght time for light
to travel from Earth to object. Format is hh:mm for all solar system
objects, except the Moon is in decimal seconds.
- SnDst true distance from
Sun center to object center, in AU.
- SnLght time for light
to travel from Sun to object. Format is hh:mm.
- Uranom Volume and Page
number of object's location in the original Uranometria, published
by Willmann-Bell, Inc.
- Uran2k Volume and Page
number of object's location in the new Uranometria 2000 edition.
- MillSA Volume and Page
number of object's location in the Millenium Star Atlas, published
by Sky Publishing Corp.
Section two controls information related to rising, transitting, and
setting. These are computed based on a refraction model that uses the
actual atmospheric and topocentric circumstances displayed on the Main
window. A text entry field is available in which you may specify a
number of decimal degrees the local horizon is above horizontal to
account for local effects.
The Limb option means that
the rise and set circumstances are based on the location of the upper
limb of the object. Center
means
that the circumstances are based on the location of the center of the
object.
Follows is a description of the Data Table columns controlled by the
second Data Selection section:
- RisTm and RisAz The local or UTC time and
azimuth when the upper limb (or center) of the object rises Today.
See note below for Earth satellites.
- TrnTm,
TrnAlt and
TrnAz
For all but Earth
satellites, this is the local or UTC time, altitude and azimuth when
the object crosses the meridian Today or, if no precession, when the
local sidereal time equals the object's right ascension.
If the object is an Earth satellite, this is the next time, highest
altitude and corresponding azimuth the satellite ever reaches above the local
horizon.
- SetTm and SetAz The local or UTC time and
azimuth when the upper limb (or center) of the object sets Today.
See note below for Earth satellites.
- HrsUp The number of hours
the object is up Today, that is, the difference between the set and
rise times. See note below for Earth satellites.
Note for time zones:
Rise and set circumstances are all
computed in local time. If the Zone Display preference (from the
Main menubar) is set to UTC then the times are converted to UTC.
Thus, when reference is made to Today it means the current local
date, not UTC date.
Note for Earth satellites:
Due to their generally rapid motions
Earth satellites often have many rising and setting events per day.
For this reason, the rise and set time for satellites are not
restrained to be during the current local day. Rather, for
satellites, XEphem displays the very next rising and setting events
that occur strictly later than the current time on the Main window,
provided they occur within 24 hours. This means that if the rise or
set time displayed is earlier than the current local time on the
Main window, it actually refers to the next day. This doesn't happen
for the other objects because their times are restricted to events
that happen just today. Similarly, we can only compute the HrsUp
column if the set time is strictly later than the rise time.
The upshot of all this is that the best way to really understand
the visibility of a satellite in your area is by graphing its
altitude over the desired time interval, or displaying all its
passes in the Night-at-a-Glance tool.
Various odd ball rising, transit and setting conditions are accounted
for and marked when they occur as in the following table. Note that in
the case of Earth satellites, "Today" really means within the next 24
hours.
| NoRise |
up some time but never rises, as such, Today. |
| NoSet |
up some time but never sets, as such, Today. |
| NoTran |
up some time but doesn't transit, as such, Today. |
| CirPol |
object is circumpolar (never goes below horizon) Today. |
| NvrUp |
object is never above the horizon Today. |
The third section in the Data Table setup window lists the current
set of Favorites. Any one may be selected
for which the angular separation between it and the object on that row
will be shown, in degrees.
The vantage point for the Separation values depends on the Equatorial preference in the Main window.
Geocentric ignores local conditions and gives the separation as seen
from Earth center. Topocentric uses the local conditions known to
XEphem. The choice is particularly critical for lunar occultations and
Earth satellites, of course, but the effect can be significant for the
planets as well. Geocentric separations between objects and the Sun
will match the magnitude of the elongation given in the Data Table
window.
Note:
Solving over a period that will
include
the rise or set times of either object is generally better performed
from the geocentric viewpoint. The refraction effect of the
topocentric viewpoint causes many arc minutes of rapid whiplash
displacement as the objects rise and set that overlays the smooth
celestial motion of the objects. This rapid position variation can
confuse the solver algorithms that expect fairly smooth functions.
4.2 Sun
This
window provides a convenient tool to download, display and manage
images
from SOHO, the Solar
& Heliospheric Observatory. Use of this
extraordinary data is courtesy of the SOHO consortium. SOHO is a
project
of international cooperation between ESA and NASA.
The SOHO data is pulled from the web site
http://sohowww.nascom.nasa.gov. The host name is defined in the XEphem
resource XEphem.SOHOhost. This may be changed if necessary by placing a
new value in the XEphem resource file.
4.2.1 Sun mouse
Moving the mouse over a loaded SOHO image will display the approximate
RA and Dec under the cursor. To do this XEphem makes an assumption
about
the scale and orientation of the image and defines the center of the
image as the position of the sun computed at the current XEphem time.
However, we have found SOHO images are not always oriented the same way
and we are not aware of a means to know the orientation
programmatically
so beware. The Carrington Rotation Number is shown in the lower right,
also as of the current XEphem time. If XEphem time differs from when
the
SOHO image was acquired the coordinates will still be correct but of
course the solar features shown in the image will not be correct.
Note that the coordinates do not take account of the different
perspective from the SOHO spacecraft. SOHO does not wander far from the
Sun-Earth line so images of the sun itself do not suffer much but this
effect is quite pronounced for Large Angle and Spectrometric
Coronagraph
images where the coordinates of background objects may be off by a
degree or more. Again, beware and check all coordinates independently
for important work.
4.2.2 Sun Control menu
Download latest
Clicking this entry will use your
Internet
connection to download the latest image from SOHO. The type and size of
the downloaded image are determined by the current selections in the
Type and Size menus.
Save downloaded image
This button is active only if the currently displayed image was
downloaded from the net and has not yet been saved. Clicking this
button will save the
downloaded SOHO image currently being displayed to the
Private XEphem directory in .gif
format.
The name of the file always begins with SOHO and includes the size,
date, time
and code name of the data product. For example, the following file name:
SOHO_512_20030802_0100_eit_171.gif
indicates the file is 512x512, was
acquired 2003 Aug 02 at 01:00 UTC and is from the 171Å channel of
the Extreme ultraviolet Imaging Telescope.
Filter Files by Type
Filter Files by Size
These options control whether the files
presented by the Files menu will be filtered by the current setting of
the Type menu or the Size menu, respectively. If a filter is not
selected then all files found will be listed.
Print...
This selection allows printing the
current SOHO view or saving it to a file. See
Printing.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the SOHO image. See Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Sun view to a movie loop.
4.2.3 Sun Files menu
This menu lists each of the SOHO image files currently found
in either the Private or Shared directories. Depending on the Filter
settings in the Control menu it will list all
images or just those that match the current setting of the Type or Size
menus.
Selecting a file from the list will display it in this window.
4.2.4 Sun Type menu
This menu lists each of the
eight data products provided by SOHO, one of which may be selected at a
time. The type selected here will be used when Downloading a file from
the Control menu, and may also limit the scope of files listed by the
Files menu if the Filter option is On in the Control menu. Follows is a
brief summary of the data product referenced by each menu entry.
Menu Entry
|
Instrument |
Notes |
| EIT 171 |
Extreme ultraviolet Imaging
Telescope |
Fe IX/X 171 Å, rendered
blue |
| EIT 195 |
|
Fe XII 195 Å, rendered
green |
| EIT 284 |
|
Fe XV 284 Å, rendered
yellow |
| EIT 304 |
|
He II 304 Å, rendered
orange |
| HMI Continuum |
Helioseismic and Magnetic Imager |
Visible Sun spots
|
| HMI Magnetogram |
|
Magnetic Sun spots
|
| LASCO C2 |
Large Angle and Spectrometric
Coronagraph |
Corona to 6 solar radii
|
| LASCO C3 |
|
Corona to 3 solar radii
|
4.2.5 Sun Size menu
This menu lists each of the three file sizes of images provided by
SOHO, one of which may be selected at a time. The size selected here
will be used when Downloading a file from the Control menu.
4.3 Moon
This
is
an image of the Moon, shaded to indicate phase. It may be flipped and
scaled as desired and many Lunar features may be labeled, including
most spacecraft landing sites. During a Lunar eclipse, the edges of
the umbra and penumbra regions are drawn as solid and dashed lines,
respectively.
The coordinate system on the Moon is such that latitude increases
towards the north and longitude increases towards the east. When facing
the Moon with the unaided eye, lunar east is towards the right. The
lunar image in XEphem is oriented with the polar axis vertical on the
screen. Letters are placed at each edge of the image to show lunar
coordinate directions.
The scrolling list on the right lists all features in the data base.
Clicking on a name will toggle its label on the map. The labels are
positioned so the center of the feature is at the lower left corner of
the label string. If the label is being turned on then the Labels View
option is also turned on if it is off.
Double-clicking will display the set of Lunar Orbiter images that
include the feature.
The Moon nods and rocks slightly as it moves through the sky. This
motion is called libration. A dot is placed on the circumference of
the image to indicate the limb position that is currently tilted most
towards Earth due to libration. The angular position of the dot is
placed accurately but the image rendering is not adjusted for
libration effects. Thus, the surface features over which the dot and
the terminator appear in the image are only approximate.
4.3.1 Moon mouse
Left button
Activating the left mouse button while
over the lunar image will display a small magnified 2x view of the
lunar surface under the cursor. The magnified image will track the
cursor as it is moved around the image. The latitude, longitude and
solar altitude of the location are displayed in the More info... window.
Right button
Activating the right mouse button while
over the lunar image will display a popup menu. It lists the name of
the
feature nearest to the cursor, the type, lunar coordinates and the
altitude of the sun as seen from that feature at the current XEphem
time. A toggle button Label
turns on or off a label on the map. A
pushbutton Set info table
loads the feature into the More info window and
will display window if it is not already up. If the Lunar Orbiter
database has been loaded, then a pushbutton Lunar Orbiter image displays the
image in which this feature lies, and also turns on the feature's label
on the main map for handy reference.
Activating the right mouse button
while
not over the lunar image but near a sky background object will pop
up a menu containing the name and magnitude of the object. There
will also be a button
Add to favorites
to assign the object to your
Favorites.
The two features may be activated together if desired by first pressing
the left button then the right button. This is helpful when trying to
locate a particular feature in the magnified view. Try to always
release the right button to dismiss the popup before releasing the
left button. If you release the left button first, the magnifying
glass will remain on the image. If you run into this, you can activate
the glass again and mop up the remains of the old glass.
4.3.2 Moon Control menu
Print...
This selection allows printing the
current Moon view or saving it to a file. See
Printing.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Moon view to a movie loop.
Field Stars...
This selection activates the Field
Star
setup window. See
Field stars.
Set Earthshine...
This brings up a window containing a
scale which allows you to set how bright the Earthshine is in the
Moon image. The value ranges from 0, black, to 10, full sun light.
Full sun light is useful when you would like to peruse the Lunar
surface but would rather not change the XEphem date to a full Moon.
This value depends on the gamma of your display. A fine discussion
of display gamma and a test image with which you can determine the
gamma value of your own display may be found at the URL:
http://www.cs.cmu.edu/afs/cs.cmu.edu/user/rwb/www/gamma.html.
Movie Demo
This button sets up an automatic
display
movie
of the Moon. This is done by setting the N Steps entry in the Main
window to a large value; setting the Step to two hours if Sky
background is Off or to one minute if it is On; and starting XEphem
looping. The movie can be stopped by
selecting this option again or by selecting Stop from the Main window.
Forget labels
This button forgets the labels that
have been added either via the popup or the list to the right. Note
this is different than turning off labels in the View menu, which only
temporarily turns of the labels but does not forget.
Close
This closes the main Moon display and,
if open, the More info window. The image is never updated while it
is closed. however if any of the fields in the More Info window are
being used for
plotting,
listing
or
solving, they continue to be updated even
when
the window is closed.
4.3.3 Moon View menu
Spacecraft
If set and the Scale is at 6, then all
spacecraft landing sites are marked and labeled on the image. If the
Scale is less than 6, then only the Apollo sites are marked.
Labels
This sets whether additional
(non-spacecraft) Lunar features may be labeled on the image. Exactly
which ones are labeled is controlled from the scrolled list down the
right or with the popup menu activated by the right mouse button. Note
that turning labels off with this button does not forget which features
are labeled, it only turns them off. To actually forget the labels, use
the Undo labels button in the Control menu.
Sky background
This sets whether to show objects
within the current field of view that are in the XEphem database
memory or available from the Field Star facility. The size and
symbol used for the object matches that of the Sky view when set for
a minimum magnitude of 12. While this option is on, XEphem will
automatically retrieve field stars if the moon position changes on
the sky
{Pen}Umbra
This sets whether to show circles at
the edges of the umbra and penumbra during a Lunar eclipse.
Also, the current subearth location is marked with an X; the
subsolar point is marked with a small open circle; and the
anti-subsolar point is marked with a small filled circle.
Flip T/B
Flip L/R
These set whether the image is flipped
vertically or horizontally, respectively.
Grid
This sets whether a coordinate grid is
drawn over the image. Each line is spaced at an interval of 15
degrees.
<IP_ADDRESS> More info...
This brings up a separate window with
additional information. The top portion of the window reports the
location of the cursor as it is moved over the image, if the left
button is pressed. It also shows the altitude of the Sun and the
times when the Sun will next rise and set at that location. The times
are in accord with the Time zone
Preferences
in the Main window.
The lower portion of the window shows the lunar longitude of sunrise,
the lunar latitude of the subsolar point, and libration information.
The longitude of the subsolar point is at +90 from the sunrise
longitude, and the longitude of the anti-subsolar point is at -90.
The libration in longitude is positive towards lunar east; latitude
is positive towards lunar north. The Limb angle is zero at lunar
north and increases towards lunar west. The Tilt is the number of
degrees the Moon is tilted towards Earth around an axis defined by
the librations in latitude and longitude. The limb location that is
tilted most towards Earth is indicated on the image by a small dot.
Any of the values in the lower portion may be
plotted,
listed or used in a
solver
algorithm. The values are always current when used in this way, even
if the main Moon view is closed. For faster looping, close the main
Moon display to prevent it from being redrawn each time.
4.3.4 Scale menu
This pulldown menu presents a list of factors by which the lunar
image may be scaled. The image is presented in a scrolled window for
panning if it is larger than the overall window.
4.3.5 Lunar
Orbiter IV
XEphem optionally supports displaying images
taken by Lunar
Orbiter IV in 1967. These images and the features database are used by
permission of
the Lunar and Planetary Institute.
Lunar Orbiter images are located in the lo directory within the Shared
directory. When these images are installed they are accessible from the
Moon view in two ways. One is to double-click an entry in the features
list down the right of the Moon view window. The other is to use the
Lunar Orbiter images button in the popup over the image in the main
Moon window. These functions are automatically disabled if XEphem
can not fund the images on startup.
The LO images are displayed in their own window. The images are large
so panning controls are available on the bottom and right edges. The
annotation
overlay may be toggled on and off with the given toggle button. A
scrolled list in the lower right corner allows choosing one from among
all the LO images which contain the current feature.
The LO images are not perfectly aligned NSEW, some are canted as much
as 30 degrees from vertical. The images are shown exactly as they were
taken. No attempt is made to register the images with the main
XEphem moon view, nor to perform flipping or scaling. The ability to
click to see the next adjacent image would have been nice but certain
technical difficulties made the results unsatisfactory and was left
out.
The image scale is approximately 300m/pixel.
4.4 Earth
This
view displays a view of the Earth with either schematic continent
outlines or a real color image. The night side may be dark or include
nightside lights. The projection may be spherical or
cylindrical "Mission Control" style. The controls available from the
menu bar across the top control the view, the display of additional
information and
the ability to overlay the ground positions of all Favorite objects.
The scales along the bottom and right edges display, and may be used
to control, the center longitude and latitude location. The button in
the lower right corner sets the latitude to exactly zero. The scale
along the left edge sets the zoom.
Any or all of the current Favorites may be
displayed on the map. Objects with defined date ranges are only shown
when they are valid. The location defined in the Main window is marked
on the map
with a plus (+).
If a solar eclipse is occurring on the Earth a small X will mark the
location of central totality. Try July 11, 1991 around 18:00 UT or May
10, 1994 around 16:00 UT.
All computations for Earth satellites are based on the NORAD SGP4/SDP4
code. This code produces the exact same output as their test
collection.
This means, however, that it is not integrated particularly tightly
with
the rest of XEphem. For example, its computations use a different model
for Earth flattening and for refraction. These and other differences
can
lead to modest inconsistencies.
4.4.1 Earth mouse
As long as the cursor is over the Earth, the four corners of the View
will display the following information about the position beneath the
cursor:
Upper left
|
Latitude and longitude
|
Upper right
|
Great circle bearing and distance
|
Lower left
|
Local Mean Time
|
Lower right
|
Local Sidereal Time
|
Left button
While the left button is depressed and located over the
Earth map, the great circle from the Main site location through the
cursor location will be drawn.
Middle button
If View » Live dragging
is On then while the middle button is depressed and located over the
Earth map, the cursor is changed to a fleur pattern. Moving the
mouse left and right is like sliding the scale at the bottom; moving
it up and down is like sliding the scale at the right. This provides
a simple method to pan the display.
Right button
If the right mouse button is clicked
while over the Earth, a popup menu appears with information related
to the location under the cursor.
If the location is near a Site,
information is presented with respect to the exact location of that
site.
If the location is not near a Site,
the
information is with respect to the latitude and longitude of the
location under the cursor.
If the location is near the current or
a trailed location of one of the displayed objects either on the
surface or in orbit, the information
is with respect to the location of that object at the time of the
trail mark.
There will also be a button labeled
Point that will center the orientation on the cursor location.
4.4.2 Earth Control menu
Print...
This selection allows printing the
current Earth view or saving it as a Postscript file. See
Printing.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Earth view to a movie loop.
Objects...
This brings up a table for controlling
how each current Favorite object is displayed.
Set Main
This sets the Latitude and Longitude
of
the Main window to that of the current position of the Earth view.
This also causes all other information and views to be updated to
reflect the new location.
Set From Main
This sets the Earth view position to
that of the Main window
Movie Demo
This sets up an automatic display
movie
of the Earth. This is done by setting the N Steps entry in the Main
window to a large value; setting the Step to 5 minutes; and starting
XEphem
looping. The movie can be stopped
by
selecting this option again or by selecting Stop from the Main
window.
Close
This causes both the Earth view and
the
extra statistics window to be closed.
4.4.3 Earth View menu
Cylindrical graphic
Cylindrical image
Displays the entire Earth surface
projected onto a cylinder. Primary advantage is the entire surface
is visible at once. Particularly good for plotting satellite ground
tracks. Major disadvantage is distortion near the poles. The
preferred width-to-height ratio for the cylindrical projection is
3.14:1. This ratio is enforced each time this projection is selected by
changing the width and maintaining the current window height, subject
to
remaining fully on screen.
Spherical graphic
Spherical image
Displays the Earth as it would really
appear from space. The primary advantage is the sense of reality and
lack of distortion. Either projection may be shown using a simple
graphical technique which draws only the outlines of the major land
features, or using a full color image, courtesy NASA's project Blue
Marble. The former is fast, the latter looks much better. The spherical
projection resizes to become a square by setting the width equal to the
height.
Weather map
Displays a global montage of satellite
cloud imagery, ice, sea and land temperatures, courtesy Space
Science and Engineering Center at the University of Wisconsin. The
image is a gif file retrieved from
http://www.ssec.wisc.edu/data/comp/latest_cmoll.gif.
It is updated once every six hours. All other graphical features of
the Earth view remain available as overlays to this image. Primary
advantage is ease in determining whether weather will effect
visibility of a satellite pass. If you have trouble accessing the
image directly from XEphem, the program will also use the file
/tmp/latest_cmoll.gif if it exists. The weather map forces itself to
become 640x480 pixels.
After any projection is selected, the window size may be directly
manipulated manually from then on as desired.
Reload map
This button is only present when the
Weather map projection is turned on. Pressing it will cause a fresh
weather map to be retrieved.
Grid
This toggles showing grids lines every
15 degrees in latitude and longitude.
Sites
This toggles whether a tiny square
will
be drawn at each location found in the currently loaded Sites file
Sunlight
This toggles whether the portion of
the
Earth's surface currently in sun light is highlighted in some
fashion. When using the Weather map or either Image projection, the
map is darkened where the Sun is currently down, and only continent
outlines are shown.
Main marker
This toggles whether a small marker is
drawn at the location currently showing in the XEphem Main window.
Nightside lights
This toggles whether the dark side of the view will include
lights visible from space. This option is only available using either
of the Image methods (not Graphics). Image is courtesy NASA.
Live dragging:
This toggles whether the display
graphics are updated immediately as the sliders are moved, or
whether graphics are only drawn after the sliders are released.
Also, if this option is on, moving the mouse while holding down the
middle button will cause the display to rotate about the pole when
moved left-and-right or about a horizontal line centered on the window
when moved up-and-down. If your system is sufficiently fast, the
effect in quite dramatic.
Inertial frame:
When On, the display point of view
remains fixed in space; when Off, it remains over a fixed location on
the earth's surface.
<IP_ADDRESS> Objects dialog
This dialog shows one row for each
active
Favorite. The columns are as follows:
Object
This is the name of the Object.
Show
Determines whether the object is shown
on the Earth map at all. If On, the object subearth location is
shown as a cross × surrounded by the loci of points at
which the object is 60, 30 and 0 (on the horizon) degrees
altitude. Clicking on the title toggles the individual buttons for all
objects.
Label
Determines whether the name of the
object is drawn somewhat above its cross. Clicking on the title toggles
the individual buttons for all objects.
Foot Print
The footprint is a set of three
contours
indicating the locations from which the object appears at 0, 30 and 60
degrees above the horizon. This toggle chooses whether to show these
contours or just the sub-earth postion. Clicking on the title toggles
the individual buttons for all objects.
 The orbit is drawn starting from the current
location of the satellite as seen from space, irrespective of
subsequent earth rotation. Clicking on the title toggles the individual
buttons for all objects.
Trail
Brings up a window to define the time
duration and labeling of the ground track of the object. See
Trails After a trail has been created, this toggle
then allows it to be turned off and on without deleting it. The
trail really is deleted if it is Off and an Update occurs. After
being deleted, this toggle again brings up the window to define
a trail. Note that the trail may be redefined as many times as
desired directly from the Trail window, it does not need to be
deleted each time.
Track
At most one button in this column may
be On. The object for which Tracking is on will remain centered
in the view each time Update occurs.
Popup ref
At most one button in this column may
be On. When right-clicking on the map with one of these buttons
on, the bearing and altitude from that location to this object
are displayed.
The remaining columns are informational only but be used for
plotted, listed or used
in a
solver algorithm. Sub lat and long are
displayed for all types of object, the others are displayed for
Earth satellites only.
Sub lat
Sub long
These columns display the latitude and
longitude at which the given object appears exactly overhead.
Alt
This is the distance from the mean
geode to the satellite.
Range
This is the line of site distance from
the current Main location to the satellite.
Range'
This is the rate of change of Range.
It
is useful for computing the doppler shift of a signal arriving
from the satellite.
Sun lit
This column is a 1 or 0 depending on
whether the satellite is in sun light. Note this is not whether the subearth point is
in
sun light.
Age Days
This is the age, in days, of the
elements used
to
compute the satellite orbit. Drag is included but elements older
than a few days will already show errors. Use the handy
Web Update button at the bottom to download the
latest elements.
4.5 Mars
This
window displays an image of Mars as it currently appears from Earth
center. The orientation is
always parallel to the Martian rotation axis. The NSEW markings are
directions on the celestial sphere.
4.5.1 Mars mouse
Left Button
If the View » More Info
window is open, then moving the mouse around over the image while
holding the left button will display the Martian latitude and
longitude under the cursor location. A magnifying glass also appears
attached to the cursor.
Right Button
Pressing the right button while over
the planet will present a popup menu. Sliding down and releasing on
the Point button in the popup will reposition the view so the
current location is centered. Repointing will also disable the shadow
and
the subearth marker until the next Update from the Main window. If
over a feature, the popup will also contain its name, type, diameter
(or largest dimension) and location. If not over a feature, just the
cursor
location is shown.
4.5.2 Mars Control menu
Print...
This selection allows printing the
current Mars view or saving it as a Postscript file. See
Printing.
User annotation
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation
Add to movie...
This selection brings up a window to allow adding the
current Mars view to a movie loop.
Close
This selection will remove the Mars
view from the screen. If it is open it will also remove the More
Info window.
4.5.3 Mars View menu
Half size
This sets whether the map is drawn at full available
resolution or at one half resolution.
Flip
T/B
Flip L/R
This sets whether the image is flipped
vertically or horizontally, respectively.
Grid
This sets whether a coordinate grid is
drawn over the image. Each line is spaced at an interval of 15
degrees. Also, unless the image has been rotated, an X marks the
center of the image, that is, the subearth location.
<IP_ADDRESS> Features...
This window displays categories of
surface features and a scrolled list of individual features sorted by
name. The features that are selected in the scrolled list are the ones
drawn on the map.
Click an entry in the scrolled list to turn it on or off individually.
Or select features by category by clicking the toggle buttons down the
left and possibly Toggle, All and None as
convenient, then clicking Apply. Ok does the same but
also closes this window.
As a special case if everything in the scrolled list is unselected and
one feature is selected, the map will be rotated to place the selected
feature in the center. This is handy for locating a feature by name.
Note that all features may be deselected easily by clicking None
then Apply.
<IP_ADDRESS> More info...
The top
portion of this window reports
the location
of the cursor as it is moved over the image, if the left button is
pressed.
Sub Earth Lat shows the Martian latitude which currently faces
the Earth. The value is computed
each time an Update is performed from the Main Menu. The scale below
allows you to set another value if desired as described below.
Central M Long shows the central meridian longitude, or simply
Martian longitude, which currently faces the Earth. The value is
computed
each time an Update is performed from the Main Menu. The scale below
allows you to set another value if desired as described below.
Seeing sets the size of your local atmospheric seeing disk in
arc seconds. The image will
be blurred to simulate the resolution under this condition.
For browsing purposes, the scale values may be changed as desired.
Adjust
any or all scales, then press
Apply to put the changes into
effect.
Forcing changes in this way will also temporarily disable the
shadow. At the time of the next Update, the correct current values
and the shadow will be reinstated. The Apply button is made
insensitive if the scale values are correct for the current time;
the button becomes sensitive only when the scales have been moved
manually.
The values in the lower portion may be
plotted, listed or used in a
solver
algorithm. The values are always current when used in this way, even
if the main Mars view is closed. For faster looping, close the main
Mars display to prevent it from being redrawn each time.
<IP_ADDRESS> Moon view...
This is a schematic view of Mars and its moons at the indicated date
and
time. In addition, background sky objects may also be displayed.
The scale at the left controls relative magnification.
The scale at the right controls the dimmest magnitude which will be
displayed. The values range from 20 at the top and 0 at the bottom.
Objects dimmer than the value specified are not shown, except that
Mars is always shown.
Nominal celestial directions are indicated at the top and right edges.
Moons are displayed only if they are geometrically visible. Use the
top view to see whether they are also in sun light.
Mars Moons mouse
The mouse may be used to identify any
object in the Mars view. Position the cursor near the object of
interest and select the right mouse button. A popup menu will appear
with the objects name, current location and magnitude.
Mars Moons Control
menu
Print...
This selection allows you to print the
current view. See
Print.
User annotation...
This selection lets you place text and
lines on the current view. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Martian moon view to a movie
loop.
Field Stars...
This selection activates the Field
Star
setup window. See
Field stars.
Telescope GoTo
This option, when available, causes
the location of
Mars
to be sent to a telescope control process. This mechanism is
the same as that provided by the Telescope facility within the Sky
view. See
Telescope
Movie Demo
This option will set up the Main
window
time step controls for a 15 minute step size and start a
loop which dramatically displays the motions
of the moons as they orbit Mars. This selection automatically disables
the
View » Sky Background
selection to insure reasonable speed. Push the button again to stop
the movie.
Close
This removes the Mars moon display,
and
the additional information window if present, from the screen.
Mars Moons View menu
Top view
Selects whether to also display
another
window, looking down on the Mars system from above the N celestial
pole. This window will tend to remain aligned above the main view
when either is resized. Moons are displayed only if they are in sun
light.
Sky background
Selects whether to also show objects
within the current field of view that are in the XEphem database
memory or available from the
Field stars
facility. The size of the object is determined by the limiting
magnitude as specified by the scale at the right. Objects are drawn
using the same symbols as used by the Sky view. While this option is
on,
XEphem will continue to retrieve field stars as required.
Bright moons
If this option is in effect, then the
diameter of all moons will be increased by 3 pixels. This option
also insures that even those moons which are dimmer than the
limiting magnitude, as specified by the scale to the right, will be
drawn with a circle of diameter 3 pixels.
Tags
Whether to show the Roman numeral
designation beneath each moon and a 1 arc-minute scale calibration
line.
Flip T/B
Flip L/R
These allow the scene to be flipped
vertically and horizontally, respectively.
More info...
This
button brings up a separate
window which
contains quantitative information about Mars's moons. All values may
be used in
plotting,
listing
and
solving.
The E and S columns are 1 if the moon is geometrically visible from the
Earth and
Sun, respectively. The P column is 1 if the shadow of the moon
currently falls on the planet. The T column is 1 if the moon is
currently transiting the planet. Otherwise the columns are 0.
The locations of the moons are given in two coordinate systems. The
first three columns are the displacements of the moons in Mars radii
with respect to the equatorial plane. The next two columns give the
RA and Dec location of the moons in the current epoch (as specified
on the Main window).
4.6 Jupiter
This is a view of Jupiter and its Galilean moons at the indicated date
and time. In addition, background sky objects may also be displayed.
The scale at the left controls relative magnification.
The scale at the right controls the dimmest magnitude which will be
displayed. Jupiter is always displayed. The values range from 20 at
the top and 0 at the bottom. Objects dimmer than the value specified
are not shown.
Equatorial directions are indicated at the top and right edges.
Moons are displayed only if they are geometrically visible from Earth.
Use the top view to see whether they are also in sun light.
The default longitude of the GRS is set to 77 degrees, where it was
in late May of 2002. This may be changed interactively in the More
Info window.
4.6.1 Jupiter mouse
The mouse may be used to identify any
object in the Jupiter view. Position the cursor near the object of
interest and select the right mouse button. A popup menu will appear
with the objects name, current location and magnitude.
4.6.2 Jupiter Control menu
Print...
This selection allows printing the
current Jupiter view or saving it to a file. See
Printing.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Jupiter moon view to a movie
loop.
Field Stars...
This selection activates the Field
Star
setup window. See
Field stars.
Telescope GoTo
This option, when available, causes
the location of
Jupiter to be sent to a telescope control process. This mechanism is
the same as that provided by the Telescope facility within the Sky
view. See
Telescope
Movie Demo
This option will set up the time step
controls in the Main window for a 15 minute step size and start a
loop which dramatically displays the motions of the moons as they
orbit Jupiter. This selection automatically disables the View » Sky Background
selection to insure reasonable speed. Push the button again to stop
the movie.
Close
This removes the Jupiter display, and
the additional information window if present, from the screen.
4.6.3 Jupiter View menu
Top view
Selects whether to display another
window above the front view with a vantage point over the pole. This
window will try to remain aligned above the main Jupiter front view
when either is resized. Moons are displayed only if they are in sun
light.
Sky background
Selects whether to also show objects
within the current field of view that are in the XEphem database
memory or available from the
Field stars
facility. The size of the object is determined by the limiting
magnitude as specified by the scale at the right. Objects are drawn
using the same symbols as used by the Sky view. While this option is
on,
XEphem will continue to retrieve field stars as required.
Bright moons
If this option is in effect, then the
diameter of all moons will be increased by 3 pixels. This option
also insures that even those moons which are dimmer than the
limiting magnitude, as specified by the scale to the right, will be
drawn with a circle of diameter 3 pixels.
Tags
Selects whether to show the Roman
numeral designation beneath each moon and a 1 arc-minute scale
calibration line.
Flip T/B
Flip L/R
These allow the scene to be flipped
vertically and horizontally, respectively.
<IP_ADDRESS> More info...
This
button brings up a separate window which contains quantitative
information about Jupiter's moons and central meridian longitude.
All values may be used in
plotting,
listing and
solving.
The E and S columns are 1 if the moon is geometrically visible from the
Earth and
Sun, respectively. The P column is 1 if the shadow of the moon
currently falls on the planet. The T column is 1 if the moon is
currently transiting the planet. Otherwise the columns are 0.
The locations of the moons are given in two coordinate systems. The
first three columns are the displacements of the moons in Jupiter
radii with respect to the celestial plane. The next two columns give
the RA and Dec location of the moons in the current equinox (as
specified on the Main window).
Value of the System II longitude of the Great Red Spot is displayed.
The value may be changed according to current information. Pressing
Enter will update the Jupiter display with the new value.
4.7 Saturn
This is a schematic view of Saturn, its rings and moons at the
indicated
date and time. In addition, background sky objects may also be
displayed.
The scale at the left controls relative magnification.
The scale at the right controls the dimmest magnitude which will be
displayed. Saturn and its rings are always displayed. The values
range from 20 at the top and 0 at the bottom. Objects dimmer than
the value specified are not shown.
Nominal celestial directions are indicated at the top and right edges.
Moons are displayed only if they are geometrically visible. Use the
top view to see whether they are also in sun light.
4.7.1 Saturn mouse
The mouse may be used to identify any
object in the Saturn view. Position the cursor near the object of
interest and select the right mouse button. A popup menu will appear
with the objects name, current location and magnitude.
4.7.2 Saturn Control menu
Print...
This selection allows printing the
current Saturn view or saving it to a file. See
Printing.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Saturn moon view to a movie loop.
Field Stars...
This selection activates the Field
Star
setup window. See
Field stars.
Telescope GoTo
This option, when available, causes
the location of
Saturn to be sent to a telescope control process. This mechanism is
the same as that provided by the Telescope facility within the Sky
view. See
Telescope
Movie Demo
This option will set up the time step
controls in the Main window for a 15 minute step size and start a
loop which dramatically displays the motions
of the moons as they orbit Saturn. This selection automatically
disables
the
View » Sky Background
selection to insure reasonable speed. Push the button again to stop
the movie.
Close
This removes the Saturn display, and
the additional information window if present, from the screen.
4.7.3 Saturn View menu
Top view
Selects whether to also display
another
window, looking down on the Saturnian system from above the
celestial N pole. This window will tend to remain aligned above the
main front view when either is resized. Moons are displayed only if
they are in sun light.
Sky background
Selects whether to also show objects
within the current field of view that are in the XEphem database
memory or available from the
Field stars
facility. The size of the object is determined by the limiting
magnitude as specified by the scale at the right. Objects are drawn
using the same symbols as used by the Sky view. While this option is
on,
XEphem will continue to retrieve field stars as required.
Bright moons
If this option is in effect, then the
diameter of all moons will be increased by 3 pixels. This option
also insures that even those moons which are dimmer than the
limiting magnitude, as specified by the scale to the right, will be
drawn with a circle of diameter 3 pixels.
Tags
Selects whether to show the Roman
numeral designation beneath each moon and a 1 arc-minute scale
calibration line.
Flip T/B
Flip L/R
These allow the scene to be flipped
vertically and horizontally, respectively.
<IP_ADDRESS> More info...
This button
brings up a separate window
which
contains quantitative information about Saturn's moons and its
rings. All values may be used in
plotting,
listing and
solving.
The E and S columns are 1 if the moon is geometrically visible from the
Earth and
Sun, respectively. The P column is 1 if the shadow of the moon
currently falls on the planet. The T column is 1 if the moon is
currently transiting the planet. Otherwise the columns are 0.
The ring tilt is displayed as the angle above or below the line of
sight to Saturn from the Sun and the Earth.
The locations of the moons are given in two coordinate systems. The
first three columns are the displacements of the moons in Saturn
radii with respect to the celestial plane. The next two columns give
the RA and Dec location of the moons in the current equinox (as
specified on the Main window).
4.8 Uranus
This is a schematic view of Uranus and its moons at the indicated date
and time. In addition, background sky objects may also be displayed.
The scale at the left controls relative magnification.
The scale at the right controls the dimmest magnitude which will be
displayed. Uranus is always displayed. The values range from 20 at
the top and 0 at the bottom. Objects dimmer than the value specified
are not shown.
Nominal celestial directions are indicated at the top and right edges.
Moons are displayed only if they are geometrically visible. Use the
top view to see whether they are also in sun light.
4.8.1 Uranus mouse
The mouse may be used to identify any
object in the Uranus view. Position the cursor near the object of
interest and select the right mouse button. A popup menu will appear
with the objects name, current location and magnitude.
4.8.2 Uranus Control menu
Print...
This selection allows printing the
current Uranus view or saving it to a file. See
Print.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Uranus moon view to a movie loop.
Field Stars...
This selection activates the Field
Star
setup window. See
Field stars.
Telescope GoTo
This option, when available, causes
the location of
Uranus to be sent to a telescope control process. This mechanism is
the same as that provided by the Telescope facility within the Sky
view. See
Telescope
Movie Demo
This option will set up the time step
controls in the Main window for a 15 minute step size and start a
loop which dramatically displays the motions
of the moons as they orbit Uranus. This selection automatically
disables
the
View » Sky Background
selection to insure reasonable speed. Push the button again to stop
the movie.
Close
This removes the Saturn display, and
the additional information window if present, from the screen.
4.8.3 Uranus View menu
Top view
Selects whether to also display
another
window, looking down on the Uranus system from above the N celestial
pole. This window will tend to remain aligned above the main view
when either is resized. Moons are displayed only if they are in sun
light.
Sky background
Selects whether to also show objects
within the current field of view that are in the XEphem database
memory or available from the
Field stars
facility. The size of the object is determined by the limiting
magnitude as specified by the scale at the right. Objects are drawn
using the same symbols as used by the Sky view. While this option is
on,
XEphem will continue to retrieve field stars as required.
Bright moons
If this option is in effect, then the
diameter of all moons will be increased by 3 pixels. This option
also insures that even those moons which are dimmer than the
limiting magnitude, as specified by the scale to the right, will be
drawn with a circle of diameter 3 pixels.
Tags
Selects whether to show the Roman
numeral designation beneath each moon and a 1 arc-minute scale
calibration line.
Flip T/B
Flip L/R
These allow the scene to be flipped
vertically and horizontally, respectively.
<IP_ADDRESS> More info...
This button
brings up a separate window
which
contains quantitative information about Uranus's moons. All values
may be used in
plotting,
listing
and
solving.
The E and S columns are 1 if the moon is geometrically visible from the
Earth and
Sun, respectively. The P column is 1 if the shadow of the moon
currently falls on the planet. The T column is 1 if the moon is
currently transiting the planet. Otherwise the columns are 0.
The locations of the moons are given in two coordinate systems. The
first three columns are the displacements of the moons in Uranus
radii with respect to the celestial plane. The next two columns give
the RA and Dec location of the moons in the current equinox (as
specified on the Main window).
4.9 Solar System
This is a graphical representation of the
solar system. The Sun is
always at the center of the screen, marked with a small circle. The
set of objects displayed are the ones from the Favorites
list that are solar system objects. Objects with defined date ranges
are only shown at valid times.
4.9.1 Solar System Scales
The three scales at the edges control the position of the observer.
The vertical scale on the left controls the distance from the
Sun.  You can also
control this with the keypad + and - keys. Using the key alone moves
by 2% little, with Shift moves by 10%.
The horizontal scale across the bottom of the view controls the
heliocentric longitude. Think of it as a rotation about the central
axis. The value of the scale is the heliocentric longitude vector
pointing straight at you. You can also control this with the keypad
Left and Right arrow keys. Using the key alone moves by 2%, with
Shift moves 10%.
The vertical scale on the right controls the heliocentric
latitude, your angle above or below the ecliptic plane. You can also
control this with the keypad Up and Down arrow keys. Using the key
alone moves by 2%, with Shift moves 10%.
Changes to the scales take effect as you drag, unless the View » All Objects
option is on in which case the change does not take effect until you
release the scale.
4.9.2 Solar System mouse
Right button
Clicking the right mouse button near
an
object will pop up a menu with additional information. RA and Dec
are displayed as of the time the dot was computed. The RA, Dec and
Mag given for the Earth is that of the Sun.
Persistent
Label toggles whether the label for the object is displayed
regardless of whether the
View
» Labels option is activated.
4.9.3 Solar System Control
menu
Print...
This selection allows printing the
current Solar System view or saving it to a file. See
Printing.
Favorites...
The Solar System view displays the
current set of
Favorites that
are in the
solar
system.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation
Add to movie...
This selection brings up a window to allow adding the
current Solar System view to a movie
loop.
Create Trails...
This button will bring up a window to
set up making a trail for each object as they travel from their
current positions. Each trail time is drawn connected together with
a solid line with each point indicated with a small dot. The time
stamps shown with the trails, if any, are always in UTC. For the
trail to be visible, the Trails option must be activated. Only one
set of trails is supported at a time. Creating new trails will
delete the old ones. The trails will also be discarded if a user
defined
object is changed or an Update occurs from the Main window. Only the
Favorites are trailed. The other solar system objects, if any, are
always shown in their current positions. See
Trails.
Movie Demo
This push button will set the Main
window Step to 5 days and start
looping
with a very large number of steps. Press the button again or use
Stop control in the Main window to stop the movie.
Live Dragging
This toggle button selects whether the
graphics are redrawn in real time as the various scale controls are
being slid, or whether the graphics are not redrawn until the mouse
is released. The response depends on the speed of the computer, display
and data bandwidth. If the system is fast enough, turning this on
can produce dramatic depth clues for complex solar system views;
also try it in Stereo.
Stereo pair
This toggle button is used to bring up
another image of the solar system from a slightly displaced vantage
point. Adjusting your gaze to fuse the two images together will
reveal a 3D image.  This effect was designed
primarily to help visualize the orbits of comets.
At the bottom of the stereo display is
a scale to control the amount of parallax to introduce. The parallax
is only introduced in the plane of the ecliptic. This works well for
low latitudes but when viewing from near the poles it just moves
everything equally.
If you prefer focusing your eyes in front of the screen, move the
parallax control somewhat to the left; if you prefer to relax your
eyes and focus at infinity then move the parallax control to the
right. You can also control this scale with the keypad slash (/) and
star (*) keys.
Close
This push button will close both the
main Solar system view and the Stereo view. If the Solar System view
is closed while the Stereo window is on, it will reappear when the
Solar System window is reactivated.
4.9.4 Solar System View
menu
Trails
This toggles whether trails, if
currently defined, are displayed. The trails may be turned on and
off as desired without loss but the trails are permanently discarded
when the next Update from the Main window occurs.
Ecliptic
This toggle button controls the
display
of a set of circles in the ecliptic plane, spaced at regular
intervals. The interval between each circle is displayed at the
upper left of the view.
Labels
This option causes each object's name
to appear.
Legs
This toggle button controls whether a
line is drawn from each object down to the ecliptic. This aids in
visualizing the 3D location of the objects.
DB too
This allows showing all objects
currently loaded into memory that lie within the solar system, in
addition to the Favorites.
5.0 Sky View
This view presents a
schematic representation of the sky showing database
objects and useful auxiliary information. A FITS file image can also
be displayed simultaneously.
The dominant center area displays each object that meets the brightness
and type filter selection criteria. Objects with defined date ranges
are
only shown at valid times. A menu bar across the top offers access to
all functions. Fast access to certain functions are available from the
surrounding toolbars. The mouse buttons can be used inside the display
area for additional functionality specific to the exact location of
the cursor when clicked.
Note that while looping with Pause set to
0 the Sky View is not updated (although all quantitative information
is always updated internally each step). This is to permit creating
plots and using other XEphem features that use many time increments to
run much more quickly if the Sky View is unmanaged or with Pause set
to 0.
If the object is an Earth satellite, its label will be surrounded in
parentheses if it eclipsed at that location.
5.1 Sky View mouse
The mouse serves many purposes in the Sky View. Exactly what it does
at any one time depends on whether it is located over an object and on
the states of some of the toolbar buttons.
No buttons:
Generally
nothing happens when the mouse is over the Sky View and no buttons
are being pressed. However, if the Corner Coordinates toolbar button
(upper right) is On, basic data describing the position of the
cursor are displayed in the upper corners whenever the cursor is
over the Sky even when no buttons are depressed. These data include:
- In the Upper left corner:
- RA, Dec and Hour angle equatorial coordinates;
- the great-circle distance and bearing between the current
position and the
point at which the left button was last clicked;
- constellation name;
- if displaying FITS image, raw image pixel coordinates. N.B. FITS coords = XEphem coords + 1
- In the Upper right corner:
- Alt, Az and Zenith horizon coordinates;
- Galactic latitude and longitude
- Parallactic angle, +/-180 +west
The coordinates are derived directly
from the screen location and know nothing of the displayed objects.
Thus, they neglect parallax (i.e., assume everything is at infinity).
If the Telescope Marker is active and a telescope control process
is reporting telescope position information, then when the cursor is
outside the Sky View the data in the corners refer to the telescope
marker position, not the cursor position. This information is not
displayed if any keyboard keys or mouse buttons are pressed.
Left button:
If
the
Region of Interest toolbar button is On and the left mouse button is
pressed, then the information in the upper left and right corners
changes into delta information, that is, the changes in the various
coordinates with respect to the position where the left button was
last pressed.
If the ROI toolbar button is On,
pressing and dragging the left mouse button draws a Region of
Interest box. This ROI can serve two roles. One is a way to zoom.
With the ROI toolbar button On, click in the Sky View with the left
mouse button and begin to draw a box surrounding a region of
interest. When the button is released, the ROI becomes fixed into
position. To perform the zoom, press Zoom In in the tool bar. The
current size, position, and ROI are saved and the Sky View is
changed to expand the new area. The Zoom Back tool bar button then
becomes available to restore the display to its previous size and
position. The Zoom In and Zoom Back buttons work as a pair for
arbitrary
levels of undo and redo. This Zooming is implemented by actually
sliding the scales around the edges of the Sky View just as if you
had done it manually. Thus, the selected area may be rotated after
the zoom due to a change in perspective in the map projection. This
is a feature.
The other use for the ROI is available
only when an image is being display. Basic statistics are computed
for the pixels that lie within the ROI box. Also only while an image
is displayed, the left mouse button may be used to position a
Magnifying
glass; graph the pixels along an arbitrary cross sectional slice
through
the image; and compute and display high quality photometric and
astrometric information about the star nearest the cursor based on 2D
Gaussian fitting. See
Image analysis.
Middle button:
While the middle button is depressed,
the cursor is changed to a fleur pattern. Moving the mouse left and
right is like moving the scale at the bottom; moving it up and down
is like moving the scale at the right. This provides a simple method
to pan the display. This feature is not yet available while
displaying an image. If the Live
dragging option is turned on (see Control » Options), the
panning occurs immediately. If this is painfully slow on your system
then turn this off so the screen is only redrawn one time when the
button is released.
Right
button:
If
the right button is clicked over the
Sky View,
then a popup menu will appear. If the button is clicked and
released, the menu will stay up and can be used like any other menu.
Or the button may be pressed and held while you slide the cursor to
the desired button and let go. Try both and use whichever procedure you
prefer.
The popup contains information and
controls germane to the exact position of the cursor when the button
was clicked. The entries in the popup menu vary depending on whether
the cursor was near an object or over empty sky. If the cursor is
near a object, data is shown which are exactly the same as that
which is available in the
Data Table window.
If a trailed object is selected, the data applies at the
time for that position. If the cursor was not near an object, basic
information based on the location of the cursor itself is shown.
The popup also offers several control
operations, as follows. Remember, only the ones relevant to the
current situation and toolbar choices will appear.
- Name will show the name of the object. If alternate names
are available they will be displayed in a pullright cascade menu.
- Type will display a brief description of the type of
object.
- Center will change the
Sky View pointing direction to place the given object (or location)
at the center of the field of view.
- Center + Zoom » is like
Center but will also zoom in or out the amount selected in the
pullright cascade menu.
- Persistent Label » on
Left on Right will toggle whether a label is drawn on the left
or right side of the current object. The label will consist of the
name and/or the magnitude, depending on which options are selected
in the SkyView » Options
Labeling section. If neither are selected, the label will consist of
the name. Persistent labels are always on, that is, they are not
subject to magnitude limits, options, or object type filtering. Note
this option is maintained separately for trailed objects and for the
untrailed objects; that is, you have independent control over
labeling for a trailed object and its currently displayed object
since the latter also always appears in the trailed list. This can
be somewhat confusing for trails which begin Now since, in effect,
the first item is drawn twice (once just because it is an object
like any other, and again as a member of the set of trail history
points).
- Place eyepiece will cause
an eyepiece symbol to be drawn centered under the mouse location. The
eyepiece shape and size are defined in the Eyepiece Setup window,
available at Control »
Eyepieces. Both the RA-Dec and Alt-Az of the location are
saved and the one matching the Display mode is used when the
eyepiece is drawn on the Sky View. In this way eyepieces can be
fixed in either coordinate system. See Eyepieces.
- Delete eyepiece will
delete the closest eyepiece covering this mouse location. The search
algorithm uses the smaller of the two dimensions of the eyepiece so
it may be necessary to get close to the center depending on the shape.
- Telescope GoTo will cause
the coordinates of the cursor to be sent to the INDI telescope control
process. The command is not issued if the coordinates are below the
horizon. This button is only present if the connected process is
running. See Telescope.
- Add to logbook will copy
pertinent position and descriptive information about the current object
to a new entry in the Observers logbook. This
selection only appears if the logbook tool window is currently open.
- New Photom ref only
appears if an image is being displayed, the 2D Gaussian image analysis
tool is up, and the cursor was clicked near a database object. If all
this is so, then said object is used as the new reference for
photometric comparisons, and the magnitude of the object from the
database is set as the reference for subsequent use.
- Show orbit... is only
present
if the selected object is a Binary system. It brings up a window
showing
the
orbit of the secondary around the primary and an ephemeris for one
revolution. See Binary Star Map for more
information.
- Add to Favorites will add
this object to the Favorites list.
- Create Trail...
will bring up a window from which a trail may be easily defined,
computed and displayed. The button is labeled Change Trail if the selected
object already has a defined trail. Only one trail per object is
supported. See Trails.
- Track will toggle object
tracking for this object. If a trail object is chosen, the tracking
will apply to the current position of the object. See the discussion
for the Control » Tracking
toggle button for more details.
- Trail is only present
if the selected object has a trail defined. If it has a trail, the
toggle state indicates whether the trail is being displayed. Note
that turning off a trail does not actually discard the trail until
the next Update occurs from the Main window.
5.2 Toolbars
|
|
|
The toolbars are divided into
three broad categories. Down the left are choices that effect How the
scene is portrayed, such as coordinate system, flipping and
magnitude limits. Across the top the choices effect What is
displayed, such as coordinate grids, local horizon, and the
classes of celestial objects. All of the buttons in the Left and
Top toolbars are just convenient shortcuts to functions that can
also be accessed from the Options and Filter windows available
in the Sky View Control menu.
The toolbar down the right side is a little different. These
buttons share a broad common theme of Where objects or
information are located. Some also effect how the mouse operates. |
5.3 Scale controls
FOV
The vertical scale on the left side
sets the vertical field of view of the display. The horizontal field
of view is determined by the width of the window at the same scale.
The FOV can be varied in 5 minute increments from 0:05 through 180
degrees. The buttons below offer a quick way to set the scale to
exactly
90 degrees and to resize the window (by changing the width) to 1:1
and 2:1 Width:Height aspect ratios. When an image is loaded, an
additional button appears labeled Image. Clicking this will resize the
window to match the aspect ratio of the image. The FOV scale may also
be changed
using the keypad + and - keys. Using the key alone moves by 2%, with
Shift moves 10%.
Alt / Dec
The vertical scale on the right side
sets either the center altitude or declination, depending on the
display mode. The value can be varied from -90 to +90 in increments
of 5 minutes. The buttons below presents a quick way to center the
scale at exactly 45, 0 or -45 degrees. The Alt/Dec scale may also be
changed using the keypad Up and Down arrow keys (make sure your NumLock
is off). Using the key alone moves by 2%, with Shift moves 10%.
Az / RA
The horizontal scale across the bottom
sets either the center azimuth or RA, depending on the display mode.
In Alt-Az mode this sets azimuth and can be varied from 0 to 359:55
degrees in steps of 5 minutes. In RA-Dec mode this sets Right
Ascension and can be varied from 0 to 23:59:40 hours, in steps of 20
seconds. The Az/RA scale may also be changed using the keypad Left and
Right arrow keys (make sure your NumLock is off). Using the key alone
moves by 2%, with Shift moves 10%.
5.4 Trails
The location of any object on the Sky view may be computed at
regular intervals and displayed by setting up a sky trail. Use the Trails Setup window to select the interval,
number of steps, formatting details and which steps you would like
annotated. The trail setup window is accessed from the popup which
appears when the third mouse button is activated when the cursor is
near an object. Any number of objects may have trails.
The trail is created by computing the location of the object at
several intervals. Each new location will be drawn with a small mark
and connected with a line to its previous location. The trails
remain correct if the display coordinate system is changed. Trails
may be turned on or off without loss of trail information.  If any point on a trail is selected
using the third mouse button the information displayed is as per the
object at that time. The times displayed next to trailed objects are in
accord with the setting of Preferences ->
Time zone.
Trail information is not subject to the
constraints in the Filter window, i.e.,
trailed objects are always shown.
Note that in Alt-Az mode, each trailed location is positioned on
the display according to the sky at the current moment. But because
of diurnal motion these trails are not useful for comparison with
the background of fixed stars. Use the RA-Dec mode for that. This is
so important (and easily overlooked) that you will see a reminder
notice to this effect the first (and only) time you create and
display a trail in Alt-Az mode.
Finally, be sure to recompute any trails if you change any of
the preferences or circumstances in the Main window.
5.5 Sky View Control
menu
This is a summary of the Sky View Control menu. Details follow.
Options...
This brings up a window with several
choices effecting the way the scene is drawn. See
Options.
Filter...
This allows selecting the types and
magnitude ranges of objects to display. See
Filter.
Print...
This allows printing the current Sky
view or saving it to a file. If an image is currently being
displayed, it will also be part of the print image. See
Printing.
List...
This brings up a window that allows
saving the objects currently displayed in the Sky View to a file.
See
List.
Horizon...
This activates the Horizon setup
window
where you can define new or load existing horizon profiles. To
actually display the Horizon profile, turn on the toggle under
Option. See
Horizon.
Field Stars...
This activates the Field Star setup
window. To display Field Stars, turn on the toggle under Options.
See
Field stars.
Favorites ...
This activates the Favorites setup
window. See
Favorites.
Eyepieces...
This brings up a window which allows
you to specify the shape, size, rotation and style of the next
eyepiece to be created. See
Eyepieces.
Whether eyepieces are shown at all is controlled by the
Control » Options »
Eyepieces option; see
Options.
Coordinates...
This brings up a simple dialog which
allows you to type in (or copy/paste) and convert among several
common coordinate systems used in astronomy. The coordinates may be
set from or used to repoint the Sky View. See
Coordinate
converter.
User annotation...
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
Add to movie...
This selection brings up a window to allow adding the
current Sky view to a movie loop.
Tracking
Tracking in this context refers to
whether the pointing direction of the Sky View will automatically be
changed each time an Update occurs from the Main window such that
the tracked object will remain centered on the display. The object to
be
tracked is selected by using the Track
option in its popup menu, as described elsewhere. When this toggle
button is sensitive and pushed-in it means that tracking is active for
one object. The tracked object will be marked with an × on the
display after each Update. If this toggle button is selected while it
is
sensitive, it turns tracking off. This is a convenient alternate method
to turn off object tracking without having to find the exact object
being tracked and use its popup Track control. When this toggle
button is insensitive and popped-out, it means that object tracking
is not active; it does nothing when selected while insensitive.
Close:
This causes the Sky view and all
supporting windows to go away.
5.5.1 Options
<IP_ADDRESS> Display mode:
Alt-Az
RA-Dec
This pair selects whether the display
coordinate system is Altitude-Azimuth or Right
Ascension-Declination. While in Alt/Az mode the display is always
topocentric; while in RA/Dec mode the display coordinate system
depends on the Equatorial preference and Equinox settings in the
Main window.
Sphere
Cylinder
This pair selects whether the display
is projected onto a sphere or a cylinder. The advantage of the
sphere is that it mimics the real sky. The advantage of the
cylinder is it shows the entire universe at once.
<IP_ADDRESS> Grid Control:
This group of controls allows you to
specify the details of an overlay coordinate grid.
Grid
Toggles the grid on or off.
Auto
If on, the size of the grid steps will
be determined automatically and shown in the text fields beneath;
if it is off, then step sizes are determined from the values in
the text fields. Typing into either field then pressing Enter will also
turn off Auto and immediately display the grid with the new step
size.
Alt-Az
RA-Dec
This pair selects in which coordinate
system the grid will be drawn.
Label
Selects whether the grid will be
labeled.
<IP_ADDRESS> View Options:
Just dots
This toggle effects how stars are
shown. When the toggle is pushed in, all stars are displayed simply
as dots of various sizes. When the toggle is released, each type of
star is displayed with a unique schematic symbol. These symbols may
be reviewed from the
Filter window.
Flip Left/Right
Flip Top/Bottom
These toggle whether the display is
shown with a flip in the left/right or the top/bottom directions,
respectively.
Equatorial plane
This toggles whether a red 3:6 dashed
line is shown along the Earth's equator projected onto the celestial
sphere. The North and South celestial poles are marked and labeled as
NCP and SCP, respectively.
Ecliptic plane
This toggles whether a red 2:2 dotted
line is shown along the ecliptic. The ecliptic is the plane of the
Earth's orbit or, as seen from Earth, the path of the Sun and the
approximate path of the planets across the sky. The anti-solar point
is marked with a small open circle. The Vernal and Autumnal equinoxes
and Summer and Winter solstice locations are marked and labeled as VEq,
AEq, SS and WS respectively. The North and South eclipic poles are
marked and labeled as
NEP and SEP, respectively.
The
edges of umbra/penumbra of
Earth are marked with open circles. If Preferences » Equatorial
is set to Topocentric, the umbra/penumbra are projected at the current
distance of the Moon and corrected for parallax; if set to
Geocentric they are projected at infinity.
Galactic plane
This toggles whether a red 1:4 dotted
line is shown along the galactic equator. The North and South galactic
poles are marked and labeled as NGP and SGP, respecively. The galactic
center is marked and labeled as GC. The outline of the
Milky Way boundary is also shown.
Eyepieces
This toggles whether eyepieces are
drawn on the Sky view, if and when any are placed.
Eyepieces are placed on the Sky view by
using the
Place eyepiece
control in the popup menu activated by the right mouse button. The
shape and style of eyepieces is defined in the
Control » Eyepieces
window. Eyepieces are only drawn if they fit entirely within the Sky
View. This selection is automatically activated when an eyepiece is
placed.
Magnitude key
This toggles whether to display a
chart
in the lower left corner showing the correspondence between dot size
and star magnitude. The scale is automatically turned off each time
an image is first displayed.
Compass rose
This toggles whether two symbols to
indicate the cardinal directions at the center of the Sky View in
each Display mode are drawn in the lower right corner. The symbol on
the right always shows the current mode, the symbol to its left the
opposite mode. The one labeled with Z and R indicates
the
local horizontal directions toward the Zenith and toward the Right; the
one labeled with N and W indicates equatorial North and
West. The symbols are not drawn near their respective poles.
Auto magnitude
When this toggle is active, the
faintest magnitudes and dot step size will automatically be set to
something reasonable based on the field of view. This option is
automatically turned on whenever the FOV changes for any reason,
unless it was turned off manually. Note that initial resource values
for faintest magnitudes and dot step size will not be honored unless
the
initial resource value for automag is also off.
Field Stars
This toggles whether
Field stars are automatically loaded and
displayed if the position, field of view, limiting magnitude or time
changes significantly. This selection turns itself off if any
difficulties ever arise in retrieving field stars.
Live dragging
This toggles whether the graphics are
redrawn in real time as the various scale controls are being slid,
or whether the graphics are not redrawn until the mouse is released.
What works best for you depends on the speed of the computer, display
and data bandwidth. If the system is fast enough, turning this on can
produce dramatic results.
Horizon map
This toggles whether to display the
local horizon profile on the Sky View and
whether objects below the horizon are drawn. The profile
linearly interpolates between points in the defining file. See
Horizon.
Clipping
This toggles whether objects
which are below the horizon are drawn. This has no effect if no
horizon is displayed.
<IP_ADDRESS> Constellation:
File name
This drop-down selection allows you to
select the file that defines constellation figures. The files supplied
with XEphem are HAReyfigs.csf and classicfigs.csf to define the figures
defined by H. A. Rey or the classic definitions, respectively. The
files shown for possible selection are those files ending with the .csf
suffix in the Shared and Private directories.
The definition file must contain exactly one figure for each of the 89
constellations. Leading white space, blank lines and lines beginning
with # are ignored. Each figure definition begins with a line
containing just its name followed by one or more lines of the form:
drawcode ra dec [comment]
where
drawcode is a numeric value indicating a drawing
instruction as follows:
0 move to ra dec
1 draw solid line to ra dec
2 draw dashed line to ra dec
ra is decimal hours or sexigesimal h:m:s
dec is decimal degrees or sexigesimal d:m:s
the remainder of the line is ignored and may be any
comments, typical is the name of a star being drawn to.
Figures
Boundaries
This pair controls whether to show
constellation figures and/or constellation boundaries.
Full Names
Abbreviations
This radio pair controls whether and
how
constellation names are shown. The choices are full names, their
3-letter abbreviations or neither.
<IP_ADDRESS> Labeling:
This portion controls labeling
options.
The sliders select how many of the brightest objects to label in
each of four categories. The count ranges from 0 on the left to All
on the right.
The label itself may consist of the Name or Magnitude or both,
depending on the state of the two buttons in the columns marked N
and M to the left of each scale. If Names and Magnitudes are both
turned on then the magnitude is drawn to the right of the name
surrounded by parentheses. Magnitudes are always drawn to the
nearest 1/10 with the decimal point removed.
Trailed entries and objects marked for Persistent Label do not
contribute towards the brightest count.
5.5.2 Filter
This window lists all classes of
objects
supported by XEphem. Using the Filter window, you may select which
classes of objects are displayed on the Sky view window. For
reference, the Filter window also contains the schematic symbol for
each type of object, and its code when used in a database file. The
symbol displayed for each class of object is that which will be used to
represent the object in the Sky view, unless Control » Options » Just
dots is selected. Note
that the symbol used to draw an Elliptical object in the Sky View is
the same as that for objects of type Hyperbolic and Parabolic if the
name of the object begins with "C/" (presumed to denote a comet).
Three scales near the bottom of the Filter window control the faintest
magnitude limit to be displayed for Stars, Solar system and Deep sky
objects. Note that trails and persistent labels are not subject to the
faint magnitude limits.
The diameter of the symbol drawn in the Sky View is the larger of the
object's actual size at the current window scale (if a size is
specified in the database entry for the object) or a size that is
proportional to the difference between the object's magnitude and the
current faintest magnitude setting.
The fourth scale in the lower left selects the number of magnitudes
binned in each dot size. Values larger than 1 are helpful for showing
very large ranges of magnitudes.
Several push buttons appear across the bottom of the Filter window
which have the usual effects: Selecting Apply
updates the Sky display according to the desired selection. Selecting Ok does the same thing but also
closes the Filter window. All
turns on all types. Toggle
swaps
which filters and Or and Off. Reset
will return the state of all Filter controls to their state when this
window first appeared or the most recent Apply.
5.5.3 Print
This allows printing the current Sky view or saving it to a file. If
an image is currently being displayed, it will also be part of the
print image. See Printing.
5.5.4 List
This window lists, sorts and writes the objects currently displayed
in the Sky View to a file. Basing the list on the Sky View allows the
selection criteria to use the full power of the Options and Filters
controls as well as the region of the sky as defined by the center and
field of view. If you wish to include all objects without regard to
position, use the Cylindrical project mode, set RA-Dec, FOV 180, Dec 0
and resize the Sky View window to show the entire universe.
At the top, the format of the file created may be specified in either
of two formats. The .edb format saves the objects in the XEphem
catalog format. This is handy for using the XEphem filtering options
to create custom catalogs. The text format is a columnar listing. The
columns that are printed are the same as those currently selected in
the Data Table, printed to the precision specified in the Preferences. A convenient button is
provided to bring up the Date Table setup window. Note that a column
need not be printed to be used for sorting, although it would seem
unusual to do so.
The center section lists several fields that may used for sorting the
list. Pick each field in the order you wish to sort the list. If you
wish to make a change to the order, you may Undo one at a time back to
the beginning or Clear the entire sequence and begin again.
The bottom section is a text field which (will) show the results of
the sort. This text field is fully editable, so you may delete specific
objects, add comments and so on as desired. N.B. If you have chosen
the .edb format, no checks are made that your edits have made the
format illegal.
Pressing the right mouse button over the text field will bring up a
popup menu, if a valid object name is found at the beginning of the
line under the cursor. This popup has buttons to Delete the object on
the current line from the list and Mark the object on the Sky View.
Across the bottom are several controls.
Save
This writes the text field exactly as
it now appears to the file named at the right of the format
checked at the top. N.B. No check is made that the format and the
extension agree.
Sort
This rebuilds the list according to
the
current settings. Use this after changing something in the Sky
View, or after changing the format or sort settings here.
5.5.5 Horizon
XEphem
allows you to create a file describing your local horizon. This window
gives you two ways to define your local horizon, and a handy way to
edit and save a horizon description.
One way to define a horizon is just to specify one altitude that will
be used
at all azimuths. To use this method, type the desired altitude in the
field provided, then type Enter or toggle the button labeled Constant On.
The other way is to draw your actual horizon profile interactively as
follows:
- Set the Sky View to display Alt-Az mode;
- set Az to 0, Alt to 90, FOV to 180 so you see your entire sky;
- click on Edit with mouse;
- draw your horizon with the mouse;
- when finished turn Edit with mouse back off;
- enter a file name;
- click Save.
Editing can in fact be performed in any mode but the above setup is the
most natural. Reload the profile later using Load.
As many profiles can be stored as desired. For example, if you
observe from several sites, you can have a profile for each.
File format
The Horizon profile file
format (suffix .hzn) and its use by
XEphem are defined as follows:
- Each line should contain exactly two numbers separated by
spaces.
- The first number is the azimuth, expressed as degrees East of
North.
- Azimuth values range from 0 up to 360 degrees. Any values
outside
this range have 360 added or subtracted until they fall in this
range.
- The lines need not be sorted by Azimuth, although they will be
sorted when used; thus the horizon map can never cross itself.
- If the file does not include the full range of Azimuths, the
end points will be connected automatically.
- It is ok to specify just one point (at any Azimuth). This will
result in a flat horizon all the way around at the specified
Altitude. This is functionally equivalent to using the Constant
method.
- The second number is degrees above horizontal.
- XEphem linearly interpolates as necessary when drawing between
the Az and Alt values in the file.
- Lines of any other form are ignored.
5.5.6 Field Stars
This activates the Field Star setup
window. To display Field Stars, turn on the toggle under Options.
See
Field stars.
5.5.7 Favorites
This activates the Favorites setup
window. See
Favorites.
5.5.8 Eyepieces
This
window allows you to specify the shape, rotation angle, size and style
of the next eyepiece marker to be placed in the Sky View. These
markers are useful to show the view through your eyepiece, simulate
the view of a CCD camera, or as simple annotation markers for any
desired purpose. Symbology on the map will show through the eyepieces,
even when they are specified as solid.
Note that this window controls the style of the next eyepiece to be
created. To actually place an eyepiece, place the mouse over the Sky
view where you want the center to be located and press the right
button. A popup menu will appear. Slide down the menu and release over Place eyepiece. When an eyepieces is
place on the sky, both the RA-Dec and Alt-Az of the location are saved
and the set
matching the Display mode is used when the eyepiece is drawn on the
Sky View. In this way eyepieces are fixed in both coordinate systems.
Set next eyepiece ...
Across the top are three sliders which set the Width, Height and Angle of the next eyepiece. Width
and Height are shown in units of degrees:minutes.
The interpretation of the rotation angle depends on the
current display mode of the Sky View at the moment a new eyepiece is
placed. When in Alt/Az mode, the angle is away from a line through the
Zenith, and when in RA/Dec mode the angle is away from the North
Celestial Pole. In both cases, the units are degrees.
Below them is a toggle that will Lock
the W and H sliders so they move together. This makes it easy to
create eyepiece shapes that are perfectly round or square.
As a special convenience for and in deference to, there is a toggle
which will create three open circles spaced to match the view through
the Telrad unit power finder.
The circles are 0.5, 2 and 4 degrees in diameter. As long as this
special toggle is pushed in, the other controls are made insensitive
to avoid interfering with the preset values for the Telrad.
Next below are pairs of toggle buttons to select the Shape and Style
of the next eyepiece. Elliptical
and Rectangular refer to
circles
and squares. Solid and Outline refer to whether the shape
will be filled in or just drawn as a border.
Field-of-View Calculators
In the central portion of the Eyepiece window are two calculators that can be used to
compute the sky angle of an optical system in two ways. The first
method uses the net focal length of the entire optical system and a
linear size on the focal plane. The technique is handy for CCD users
who want to find the sky angle subtended by each pixel or the entire