XEphem

pronounced eks i fem´

Version 3.7.3

  Reference Manual

© 1990-2008 Elwood Charles Downey
 

1. Introduction
   1. Quantitative information
   2. Local circumstances
   3. Launching XEphem
      1. Shared and Private Directories
      2. Main window control
   4. Time and angle formats
2. Main Window
   1. Main's Help menu
   2. Menu bar
      1. File
      2. View
      3. Tools
      4. Data
      5. Preferences
   3. Sections
      1. Local
         1. Site Selection
      2. Time
      3. Calendar
      4. Night
      5. Looping
3. File menu
   1. System log
   2. Gallery
      1. File format
   3. Network Setup
   4. External Input
4. View menu
   1. Data Table
      1. Data setup
   2. Sun
      1. Sun mouse
      2. Sun Control menu
      3. Sun Files menu
      4. Sun Type menu
      5. Sun Size menu
   3. Moon
      1. Moon mouse
      2. Moon Control menu
      3. Moon View menu
         1. More info...
      4. Scale menu
      5. Lunar Orbiter IV
   4. Earth
      1. Earth mouse
      2. Earth Control menu
      3. Earth View menu
         1. Objects dialog
   5. Mars
      1. Mars mouse
      2. Mars Control menu
      3. Mars View menu
         1. Features...
         2. More info...
         3. Moon view...
   6. Jupiter
      1. Jupiter mouse
      2. Jupiter Control menu
      3. Jupiter View menu
         1. More info...
   7. Saturn
      1. Saturn mouse
      2. Saturn Control menu
      3. Saturn View menu
         1. More info...
   8. Uranus
      1. Uranus mouse
      2. Uranus Control menu
      3. Uranus View menu
         1. More info...
   9. Solar System
      1. Solar System Scales
      2. Solar System mouse
      3. Solar System Control menu
      4. Solar System View menu
5. Sky View
   1. Sky View mouse
   2. Toolbars
   3. Scale controls
   4. Trails
   5. Sky View Control menu
      1. Options
         1. Display mode:
         2. Grid Control:
         3. View Options:
         4. Constellation:
         5. Labeling:
      2. Filter
      3. Print
      4. List
      5. Horizon
      6. Field Stars
      7. Favorites
      8. Eyepieces
      9. Coordinates
      10. User annotation
   6. Sky View Images menu
      1. Load and Save FITS images
      2. Image Analysis Tools
         1. Brightness and Contrast
         2. Cross section Slice
         3. Magnifying Glass
         4. Region of Interest
         5. 2D Gaussian Measurements
      3. Registration
      4. WCS Solver
   7. Sky View Favorites menu
   8. Sky View Telescope menu
      1. INDI Test Drivers
      2. INDI Configuration window
      3. INDI Control Panel
      4. FIFO Control
   9. Sky View History menu
   10. Sky View Binary Star Map
6. Tools menu
   1. Plot values
   2. List values
   3. Solve equation
   4. Find close pairs
      1. Close Pairs Control menu
      2. Close Pairs Options menu
      3. Close Pairs Algorithm
   5. Night at a Glance
   6. Coordinate converter
   7. Observers logbook
   8. Movie loop
7. Data menu
   1. Files
      1. Files Control menu
      2. File format
         1. General format rules
         2. Format Details
         3. Magnitude models
      3. Notes
      4. Two-line Earth satellite element sets
   2. Index
   3. Favorites
   4. Download
   5. Field Stars
      1. Hubble GSC
      2. USNO A or SA catalogs
      3. Proper Motion catalogs
      4. Skip likely duplicates
      5. Notes
8. Preferences
   1. Fonts
      1. XLFD
   2. Colors
      1. Colors Control menu
      2. Star colors
   3. Save
9. Multifunction Tools
   1. Trails
   2. Printing
   3. Annotation
10. Credits
11. Notes
    1. Horizon
    2. glob Patterns
    3. Accuracy
    4. TODO
    5. Known Bugs
    6. History

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.
  

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.

1.3 Launching XEphem

1.3.1 Shared and Private Directories

1.3.2 Main window control

1.4 Time and angle formats

2.0 Main Window

2.1 Main's Help menu

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

• 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

• 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

• 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

• 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

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.
  

2.3.1.1 Site Selection

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.

• UTC Time The UTC time.

• 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

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).

• 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:
  
  
  1. clicking Now under the calendar
  2. setting Step to Clock
  3. setting N Steps to something large and then
  4. 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.

3.0 File menu

3.1 System log

3.2 Gallery

Close the Gallery window.

Reinitialize the list. This also occurs each time the Gallery window is opened.

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

<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

• 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.

3.4 External Input

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.

• 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.
  

4.1.1 Data setup

• 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.

• 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 and TrnAlt For all but Earth satellites, this is the local or UTC time and altitude when the object crosses the meridian Today, i.e., when its azimuth is true south 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 time and highest altitude the satellite ever reaches above the local horizon (at whatever azimuth).

• 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.
  

4.2 Sun

4.2.1 Sun mouse

4.2.2 Sun Control menu

This selection brings up a window which allows text and lines to be drawn over the SOHO image. See Annotation.

This selection brings up a window to allow adding the current Sun view to a movie loop.

4.2.3 Sun Files menu

4.2.4 Sun Type menu

4.2.5 Sun Size menu

4.3 Moon

4.3.1 Moon mouse

4.3.2 Moon Control menu

This selection brings up a window to allow adding the current Moon view to a movie loop.

4.3.3 Moon View menu

4.3.3.1 More info...

4.3.4 Scale menu

4.3.5 Lunar Orbiter IV

4.4 Earth

4.4.1 Earth mouse

4.4.2 Earth Control menu

This selection brings up a window to allow adding the current Earth view to a movie loop.

4.4.3 Earth View menu

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.

4.4.3.1 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.

Orbit

Determines whether to draw the orbit of an earth satellite. 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

4.5.1 Mars mouse

4.5.2 Mars Control menu

This selection brings up a window to allow adding the current Mars view to a movie loop.

4.5.3 Mars View menu

This sets whether the map is drawn at full available resolution or at one half resolution.

4.5.3.1 Features...

4.5.3.2 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.

4.5.3.3 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

Mars Moons Control menu

This selection brings up a window to allow adding the current Martian moon view to a movie loop.

Mars Moons View menu

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.