XEphem

pronounced eks i fem´

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.
  

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 https://www.ncei.noaa.gov/products/world-magnetic-model 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 Millennium 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, 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.
  

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.

4.6.1 Jupiter mouse

4.6.2 Jupiter Control menu

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

4.6.3 Jupiter View menu

4.6.3.1 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

4.7.2 Saturn Control menu

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

4.7.3 Saturn View menu

4.7.3.1 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.

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

4.8.2 Uranus Control menu

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

4.8.3 Uranus View menu

4.8.3.1 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

4.9.1 Solar System Scales

4.9.2 Solar System mouse

4.9.3 Solar System Control menu

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

4.9.4 Solar System View menu

5.0 Sky View

5.1 Sky View mouse

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
  

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 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.

• 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

5.4 Trails

5.5 Sky View Control menu

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

5.5.1 Options

5.5.1.1 Display mode:

5.5.1.2 Grid Control:

5.5.1.3 View Options:

5.5.1.4 Constellation:

5.5.1.5 Labeling:

5.5.2 Filter

5.5.3 Print

5.5.4 List

5.5.5 Horizon

1. Set the Sky View to display Alt-Az mode;
2. set Az to 0, Alt to 90, FOV to 180 so you see your entire sky;
3. click on Edit with mouse;
4. draw your horizon with the mouse;
5. when finished turn Edit with mouse back off;
   
6. enter a file name;
7. click Save.
   

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

5.5.7 Favorites

5.5.8 Eyepieces

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.

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 detector. Another good use of this form is for photographers using film to find the amount of sky that will fit on their film. To cover this wide range of applications, the measures may be specified in any of several common units by adding the appropriate suffix. Default units are shown in parentheses.

The second calculator uses the apparent field of view while looking into an eyepiece and divides this by the magnification, which in turn is found from the ratio of focal lengths for the primary mirror and the eyepiece. Typical eyepieces provide about 45 degrees apparent fields of view, and some premium ones can go to 60 degrees or more. After using either method, the resulting sky angle can be assigned to the Width or Height scale for the next eyepiece by using the Set W and H buttons to the right.

This portion of the Eyepieces window allows you to Add the current eyepiece settings to a list of favorites. A simple name is chosen automatically but you may change this to be more meaningful to you. Each such eyepiece may be Deleted from the set or put to Use by using the buttons on the left. To the right of each eyepiece is a reminder of its width, height and a code letter for its shape and size.

The buttons below the table of favorite eyepieces allow you to Save and later Load the table to a file. These files have the extension .epd. When saving, the new file is always created in the Private directory. When loading, files with this suffix are first checked for in the Private directory and if not found in the Shared directory. The suffix is automatically added if not entered in the file name field. The file named in the Save field is also the file that is automatically loaded when XEphem starts. This file name can be saved in the Preferences » Save window in the Skyview -- Eyepieces section as EyePDefFile.

This portion of the Eyepieces window allows you to Save and later Load the set of eyepieces currently defined on the Sky View to a file. These files have the extension .epp. When saving, the new file is always created in the Private directory. When loading, files with this suffix are first checked for in the Private directory and if not found in the Shared directory. The suffix is automatically added if not entered in the file name field. The file named in the Save field is also the file that is automatically loaded when XEphem starts. This file name can be saved in the Preferences » Save window in the Skyview -- Eyepieces section as EyePPosFile.

After at least one eyepiece has been placed in the Sky View, a button at the bottom of this window will become available to permanently Delete all placed eyepieces currently anywhere on the Sky View. You may also delete them individually from the Sky View from the right-click popup or if you just want to temporarily turn all Eyepieces off and back on later, use the Eyepieces control in the Control » Options window.

Across the bottom are buttons to Close the window and Help to get more information. Closing the window has no effect on eyepieces already placed in the Sky View.

5.5.9 Coordinates

5.5.10 User annotation

5.6 Sky View Images menu

5.6.1 Load and Save FITS images

5.6.2 Image Analysis Tools

5.6.2.1 Brightness and Contrast

5.6.2.2 Cross section Slice

Full pixel range toggle when set scales the vertical scale to the full range of pixel values in the image, else scales to the pixel range from Lo to Hi as defined in the Brightness and Contrast section.

5.6.2.3 Magnifying Glass

5.6.2.4 Region of Interest

• Length of the diagonal;
• Width and height of the region;
• Value and location of the cursor as you draw the ROI;
• Value and location of the largest pixel in the ROI;
• Value of the minimum pixel;
• Mean value of all ROI pixels;
• Median value of all ROI pixels;
• One Standard Deviation of the pixel values about the mean.

5.6.2.5 2D Gaussian Measurements

• Relative magnitude difference and error estimate between the current star and the reference star;
• Position of the star, in image coordinates and in RA/Dec if WCS header fields are present;
• Full-width-half-max of the star in each dimension in pixels, and in arc seconds if the image scale is known from header fields CDELT1 and CDELT2;
• The pixel value representative of the noise level base in the area (B in the above equation);
• The pixel value of the peak of the Gaussian fit (A+B in the equation).

5.6.3 Registration

5.6.4 WCS Solver

Commences the search for a solution using the image currently in the Sky View and the parameters in the various fields above. If a solution is found, each star used in the solution will be circled and statistics about the quality of the solution will be presented. The WCS fields that characterize the solution are written into the FITS header. If you like the solution, Save the image and this solution will be saved with the image and searching will not be needed next time.

Mark stars

Clicking this button will draw a small circle around each group of pixels in the image the algorithm considers to be a star. Use this to choose good values for Burned out and S/N ratio.

The first step is to supply suitable seeds values for the center of the image, the image scale and any suspected rotation. If the FITS image header contains fields with these values, enter the names of the fields in the spaces provided and they will be extracted automatically when the image is loaded. If the header does not contain this information, or the units are not correct, then seed values must be entered manually in the fields provided. Note that the pixel scale values must have the correct sign since the algorithm automatically takes into account rotation but not flipping.

The second step is to set the SNR value so that Marking stars finds most of the brightest and well-formed star-like objects in the image, without also finding bogus star candidates. Also, if the image was over exposed so that very bright stars are washed out, eliminate these by reducing the value for burned out stars.

Once good stars are being marked, the last step is to indicate how accurately star centroids can be determined and how accurate any solution is likely to be using the bottom two fields of the form.

Another issue is to use an appropriate field star catalog. More stars  is not  necessarily better. For example, the GSC 2.2 goes to mag 18 but also tends to have more bogus entries near very bright stars. If your image contains a very bright star, take note of the field stars that are near it; you might do better with the GSC 1.2 than 2.2 catalogs.

After adjusting any field, click Go. If a solution is found, the stars used in the fit will be marked and statistics about the fit will be displayed.

This algorithm has proven to be very robust over the years. With a little practice it can usually be made to work quite well.

5.7 Sky View Favorites menu

5.8 Sky View Telescope menu

5.8.1 INDI Test Drivers

5.8.2 INDI Configuration window

5.8.3 INDI Control Panel

5.8.4 FIFO Control

1. Inbound: A marker may be placed on the Sky View by writing a text string to the fifo named fifos/xephem_in_fifo. The format allows for sending either equatorial or horizon coordinates. To send an equatorial coordinate, the format is "RA:X Dec:Y", where X and Y are in radians at epoch 2000.0. To send a horizon coordinate, the format is "Alt:X Az:Y", where X and Y are in radians. The Sky View center pointing position will be changed if necessary to make the marker visible. XEphem attempts to open this fifo each time the Sky View window is opened and closes it when the view is closed.
   
   
2. Outbound: If a process has the fifo named fifos/xephem_loc_fifo open for reading when the Sky View popup menu is activated, then the menu will offer a button to send the cursor position to this fifo. The format is the same as a line in .edb format. If it is not already open XEphem attempts to open this fifo each time the popup is activated, and leaves it open until writing to it fails. Each position sent to the fifo is added to the Telescope history list.
   

5.9 Sky View History menu

Apply

puts the entry into effect, in the same way as choosing it from the pulldown menu.

Up
Down

moves the entry up or down in the list.

Delete

removes the given entry.

Replace

replaces the entry with the current Sky View settings.

Add

captures the current Sky View settings and creates a new History entry. A default name will be created but you should probably change it to something more descriptive if you plan to Save the list.

Save

writes all of the current History entries to a file. The file name is xephem_skyhist and will be created in the Private directory. You really don't want to know the format of this file.

Load

reads an existing file of History entries that has been previously Saved and makes them the current set.

5.10 Sky View Binary Star Map

6.0 Tools menu

6.1 Plot values

Enter a short title for the plot information in the text field provided. When XEphem first writes to a plot file, it will place the contents of the title text field, if it is not empty, into the file as a comment. All lines within a plot file that do not begin with an alphanumeric character are considered comments and are ignored. If the first line of a file is a comment, XEphem will use it as the title when it displays the plot.

6.2 List values

6.3 Solve equation

The windows which contain the fields used in the function being solved need not be visible while solving is in progress. However, the field must be active, for example their row and column must be selected if they are in the Data table.

The Close button removes the Solving window from the screen; it does not effect actual solver operation in any way.

A successfully compiled function is evaluated each time XEphem updates. Whenever the function is compiled it is also evaluated using freshly updated values. In this way, the Solve window can actually be used as an arbitrary astronomical calculator at any time, whether or not solving is actually active.

Solving periodic functions can lead to solutions far from the intended range. You will get best results if you can start the search near the expected answer and with a modest step size that will reach the the nominal solution within a few steps. You can use the plotting feature to study a function and get an idea of the solution, then use the solver feature to zero in.

Each plot file may be added to a movie loop or overlayed with text or graphical annotation using the menu items in the Control menu of each plot.

6.4 Find close pairs

1. Set the desired maximum separation, in degrees, and faintest magnitude.
   
2. Set other options via the Options menu, described below.
3. Start the scan via the Run button in the Control menu.
4. When the scan completes, all pairs meeting the criteria will appear in the scrolled list.
   

• Object 1 Magnitude
• Object 1 Name
• Object 2 Magnitude
• Object 2 Name
• Separation, in Degrees:Minutes:Seconds
  

6.4.1 Close Pairs Control menu

6.4.2 Close Pairs Options menu

6.4.3 Close Pairs Algorithm

6.5 Night at a Glance

6.6 Coordinate converter

Close

Closes this window

Sky Point

Centers the Sky View at the current coordinates.

Eyepiece

Places an eyepiece in the Sky View at the coordinates shown. The Sky View is not recentered. In order to be drawn the Sky View Eyepieces Option must be turned on.

Get Sky

Loads each field from the current center position of the Sky View.

Canonize

Reformats each field in a consistent manner for easier viewing.

6.7 Observers logbook

This brings up a scrolled list showing all entries in the logbook whose fields match those selected in the S column. The field may contain glob patterns for a textual match or be preceded with < or > for a numerical range match. Only those fields selected with the L column will be shown, and they may be sorted by the field selected in the K column.

You may Save the resulting scrolled list to a text file using the file name field provided. Right-clicking on an entry in the scrolled list will mark the location of that log entry in the Sky View based on its RA2000 and Dec2000 field values.

6.8 Movie loop

7.0 Data menu

7.1 Files

7.1.1 Files Control menu

This is a handy shortcut to open the object index.

This deletes all loaded data. The files on disk are not effected.

This reloads all catalogs currently loaded. This is handy when catalogs have been updated on disk, perhaps by some by some automatic means.

Listen for database objects arriving via a fifo from another process. XEphem attempts to reopen the fifo each time the button is pressed. The file name of this fifo is "fifos/xephem_db_fifo" in either the Private or Shared directory. All relevant displays are automatically updated when data arrives via this fifo. The format of the fifo data is exactly the same as for any XEphem database file. Due to the way the fifo data is read and processed, it is important that each line be terminated with a newline; incomplete last lines can result in loss of information.

If this toggle is on then when a new database file is loaded and it defines exactly one object, it will also be assigned to the list of Favorites. This feature also applies for files loaded when XEphem first starts.

This toggle turns on or off support for XEphem 3.6's new support for alternate names. It is motivated entirely by performance. Recording alternate names and checking for duplicates is quite expensive and if not needed can speed up loading and deleting catalogs significantly. If this toggle is On then when a new database catalog is loaded each entry's alternate names, if any, will be checked for already being loaded and not loaded if found, and new alternates will be stored for display and subsequent checking. If this toggle is Off, only the first name of each entry is stored and no duplicate names are checked. Note that even when this option is Off, deleting a catalog still requires XEphem to remove all alternate names that might have been recorded when the catalog was loaded, so the full performance advantage is only achieved if this option was off when each catalog is loaded.

Closes the Data Base window.

7.1.2 File format

7.1.2.1 General format rules

• Each object occupies one line in the file.
• The order of objects in a file does not matter.
• Lines beginning with anything other than a-z, A-Z or 0-9 are ignored and may be used for comments.
• Lines are separated into Fields using commas (,).
• Fields may be further subdivided into Subfields with vertical bars (|).
• All date fields may be in either of two forms:

1. month/day/year, where day may contain a fractional portion. examples: 1/1/1993 and 1/1.234/1993 . Note the format of dates in database files is always M/D/Y, regardless of the current XEphem Date format Preference setting; or
   
   
2. the year as real number as indicated by the presence of a decimal point, such as 1993.123.
   

7.1.2.2 Format Details

7.1.2.3 Magnitude models

7.1.3 Notes

XEphem uses a different window to manage Field star catalogs.

XEphem ships with a few perl scripts which might be helpful for converting databases in other formats into XEphem format. These scripts are in the tools/ directory of the source distribution tree.

7.1.4 Two-line Earth satellite element sets

AAAAAAAAAAAAAAAAAAAAAAAA
1 NNNNNU NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN
2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN

Line 0 is a twenty-four character name.

Lines 1 and 2 are the standard Two-Line Orbital Element Set Format identical to that used by NORAD and NASA. The format description is:

When reading a TLE entry, XEphem assigns the valid range of dates for a set of elements to the greater of 100 days or the time required for the mean motion to change by one percent either side of the element epoch.

7.2 Index

7.3 Favorites

• from the Data » Index window by browsing the objects currently loaded in memory then clicking Favorite;
• from buttons labeled Favorite located in several dialogs throughout XEphem;
  
• from buttons in the popup menus of several views when clicked over displayed objects; and
  
• by entering its .edb format definition in the text field near the bottom of the Favorites window and clicking Add edb.
  Note this field may also be used to edit an existing Favorite in-place.

Del

removes the entry from the Favorites list

Up and Down arrow buttons

move the entry up and down to arrange the Favorites into any designed order. This is useful where Favorites define rows such as in the Data Table and Night at a Glance windows.

Use

specifies whether to use or hide the entry from the rest of XEphem without actually Deleting it.

7.4 Download

7.5 Field Stars

7.5.1 Hubble GSC

7.5.2 USNO A or SA catalogs

7.5.3 Proper Motion catalogs

7.5.4 Skip likely duplicates

7.5.5 Notes

8.0 Preferences

8.1 Fonts

This window lets you change most of the fonts used by XEphem. The basic technique is to specify a font, use the four toggle buttons to choose which action to take then perform the action in a particular font context by clicking in the menus accessed from the menubar across the top.

8.1.1 XLFD

8.2 Colors

8.2.1 Colors Control menu

8.2.2 Star colors

8.3 Save

Major: In the opinion of the author these preferences are sufficiently interesting that they are likely to be worth saving and automatically restoring between one invocation of XEphem and the next.

Minor: Everything else, presumably less critical in nature. It is expected that you are likely to change these preferences frequently in due course while operating XEphem yet they do not cause major effects on program behavior so saving them at any one particular setting is not especially compelling. Minor preferences are things like window size and position, scale settings which only effect views, and all of the Sky View Filter and Option settings.

This distinction is of course rather arbitrary so please take care when changing and saving preferences so the ones you want are saved.

The number of preferences in each class currently tagged for saving is indicated by messages near the top.

In the expanded view, each preference and its value are shown exactly as it will appear in the disk file if Saved. Those preferences which differ from the last time they were Saved, or since XEphem was started if no Save has yet occurred, are marked with a bullet. Major preferences are marked with a solid bullet, Minor preferences with an hollow bullet. A toggle next to each preference allows individual selection over whether the preference will be written to disk on the next Save. After each Refresh, the toggles are set for those preferences found to have changed since the last Save if their class is set to be automatically tagged. Each toggle may be changed manually in either direction to override this automatic behavior on an individual basis if desired but not these will be overridden with the next Refresh.

In the collapsed view, if at least one Major preference is out of date in a category, a solid bullet is placed next to the category heading; otherwise if at least one Minor preference is out of date a hollow bullet is used.

Note that the information in this window does not automatically track changes in preferences as XEphem is used. You must use Refresh to update the status manually when desired. In particular, the values which are Saved are what they were the last time Refresh was performed, not what they actually are at the moment Save is activated.

9.0 Multifunction Tools

9.1 Trails

9.2 Printing

9.3 Annotation

1. click New to create a blank entry,
2. type in the desired text,
3. click Place to begin the placement procedure,
4. move the cursor to position the text where desired,
5. click and hold to anchor the text and begin drawing a line,
6. move the pencil cursor to position the far end of the line as desired,
7. release.

10.0 Credits

Thanks to Lutz Mandle for restoring SOHO support in 2012; showing sun in moonview; proxy support in web downloads; improved horizon clipping and correct use of Sky View options in individual planetary views.

Enormous advances in data quality were contributed by the late Guillermo Andrade Velasco.

The Blue Marble project at https://visibleearth.nasa.gov/collection/1484/blue-marblefor their wonderful whole-earth color images.

Corrections for ecliptic longitude from Adrian Robinson, adrianprobinson@yahoo.co.uk

The stellar spectra colors are based on work by Mitchell Charity, mcharity@lcs.mit.edu, at https://www.vendian.org/mncharity/dir3/starcolor.

Thanks to Paul Schlyter for some improved anomaly code.

Dean Huxley contributed improved constellation figures and improved the Tycho Hipparcos data base.

Thanks to Thomas Conze, thomas.conze@gmx.net, for several great patches.

Thanks to Matei Conovici, cmatei@profis.ro, for making Sky View's "live report" option a saveable preference.

Several nice tweaks and some thorough debugging from John O'Donnell, jmodonnell@earthlink.net.

Thanks to Jean-loup Gailly and Mark Adler for zlib.

Thanks to Eric S. Raymond for his fine implementation of base64.

Milky Way contour by Pertti Paakkonen, ppaakko@cc.joensuu.fi, in turn based on map from http://www.ebicom.net/~rsf1/fun/sm-new.htm copyright (c) 1972,2001, R.S. Fritzius, may be reproduced for non-commercial purpose.

The local magnetic declination model is from the DoD World Magnetic Model as published at https://www.ncei.noaa.gov/products/world-magnetic-model

Thanks to Fridger Schrempp, fridger.schrempp@desy.de, for his long term encouragement of the project, and particularly for many suggestions to improve ease of use.

Thanks to Wolfgang Steinicke of www.ngcic.org for allowing use of his corrected NGC and IC catalogs.

Earth satellite orbit propagation is based on the NORAD SGP4/SDP4 code, as converted from FORTRAN to C by Magnus Backstrom, b@eta.chalmers.se. See "Spacetrack Report Number 3: Models for Propagation of NORAD Element Sets" at https://www.celestrak.org/NORAD/documentation/spacetrk.pdf

Improvements to Delta T code, help and wording contributed by Neal McBurnett, nealmcb@bell-labs.com.

Any parts of the USNO SA2.0 catalog that are included with XEphem distributions are done so with the following understandings:

It may not be the latest version, check with http://ad.usno.navy.mil

If you paid for XEphem, you paid for the software, not this catalog. The catalog is available free from the USNO.

Inclusion of the SA2.0 catalog does not imply an endorsement of XEphem by USNO; nor did I have privileged access to the catalog; nor does the US Government affirm or guarantee that XEphem works properly in any way.

Thanks to Robert Lane, roblane@alum.mit.edu, for Uranonmetria 2000 work.

Martian relief map completed June 2000 using data from Mars Orbiter Laser Altimeter on board the Mars Global Surveyor, operated by the Jet Propulsion Laboratory, NASA. See https://marsprogram.jpl.nasa.gov/mgs

The near real-time weather map in the Earth view is provided by the Space Science and Engineering Center at the University of Wisconsin. See their web site at https://www.ssec.wisc.edu/data

The XEphem logo was contributed by Jonathan Adams, jfadams@mail.arc.nasa.gov. The galaxy background image is from Galaxy Photography, www.galaxyphoto.com.

For the years 1999-2010 the natural satellite ephemerides for Mars, Jupiter, Saturn and Uranus are based on developments in mixed functions computed and contributed at Bureau Des Longitudes, https://www.bdl.fr by J.-E. Arlot, Ch. Ruatti and W. Thuillot. Many thanks!

Outside this range, Jupiter's moons based on information in "Astronomical Formulae for Calculators" by Jean Meeus. Richmond, Va., U.S.A., Willmann-Bell, (c) 1982. Saturn's moons based on code and ideas supplied by Dan Bruton, Texas A&M, astro@sfasu.edu. For all dates, ring tilts based on "RINGS OF SATURN" program by Olson, et al, Sky & Telescope, May 1995, page 95. C code as converted from BASIC by pmartz@dsd.es.com (Paul Martz).

Thanks to Monty Brandenberg, mcbinc@world.std.com, for his assistance and solution to the unaligned access messages on Digital UNIX.

Thanks to Christophe Magneville, cmv@hep.saclay.cea.fr, for finding an array subscript and a numeric overflow problem in libastro.

Thanks to Jean-Etienne Lamiaud for a fix to prevent gif color tables from hogging more than their share of X colormap entries, many corrections to xephem_sites, and a nice speedup to Sky View depth sorting.

Thanks to Egil Kvaleberg, egil@kvaleberg.no, for key idea on how to support 8 bit FITS images.

Thanks to Stuart Levy, slevy@ncsa.uiuc.edu, for his work converting the Tycho ESA mission database adc.gsfc.nasa.gov:/pub/adc/archives/catalogs/1/1239 into xe format.

Images of Saturn from STScI.

Many formulas and tables are based, with permission, on material found in: "Astronomy with your Personal Computer" by Dr. Peter Duffett-Smith, Cambridge University Press, (c) 1985.

The high precision planet positions were implemented for XEphem by Michael Sternberg <sternberg@physik.tu-chemnitz.de> based on the papers

1. "Planetary Theories in rectangular and spherical variables: VSOP87 solution" by Bretagnon P., Francou G., in Astron. Astrophys. 202, 309 (1988), ftp://ftp.bdl.fr/pub/ephem/planets/vsop87/, and
2. "Representation of planetary ephemerides by frequency analysis. Application to the five outer planets" by Chapront J., Astron. Astrophys. Suppl. Ser. 109, 181 (1995), ftp://adc.gsfc.nasa.gov/\ pub/adc/archives/journal_tables/A+AS/109/181.

The high precision Moon code was also implemented for XEphem by Mr. Sternberg based on code supplied by Stephen L. Moshier <moshier@world.std.com> at ftp://ftp.std.com/pub/astronomy/selenog.zip. Mr. Sternberg also incorporated the algorithm for deltaT, based on code also provided by Mr. Moshier. See the comments in deltat.c for full references. My greatest thanks to Messrs. Sternberg and Moshier for their generous and kind assistance in making XEphem a program of first-class accuracy.

The improved lunar libration trig series fit to JPL DE403 was provided by Stephen L. Moshier, <moshier@world.std.com>.

Many thanks to Michael Naumann, Michael.Naumann@eso.org, and Miguel Albrecht, malbrech@eso.org, at ESO and Tim Kimball, archive@stsci.edu, at STScI for their help and support accessing the DSS at their institutions. And thanks to ESO and STScI in general for offering this service at all.

Thanks to Seiichi Yoshida, seiichi@muraoka.info.waseda.ac.jp, for a subtle fix to the constellation code in 3.1.

The sample spacecraft elements were furnished by Ron Baalke, baalke@jpl.nasa.gov.

Thanks to Vance Haemmerle, vance@toyvax.Tucson.AZ.US, for his updated and appended lists of spacecraft elements, and work on improvements to the solar system plotting of long-period trail sequences.

Thanks to Jeroen Valkonet (jeroenv@cvi.ns.nl) for planting the seed which grew into the new bitmap clipmask approach of drawing the stars.

Thanks to Jim Bell, jimbo@cuspif.tn.cornell.edu, and the team at Mars Watch for encourage, support and ideas for the first Mars albedo map in XEphem. The map as of Version 3.3 is from http://maps.jpl.nasa.gov/mars.html

Thanks to Dimitromanolakis Apostolos <apdim@grecian.net> for his contribution leading to support for fetching DSS in gzipped form.

Thanks to Miguel Albrecht, malbrech@serv2.hq.eso.org, at ESO for his assistance and support of their fine Web access facilities to the GSC.

Rotated trail text uses the xvertext package. Here is the copyright:

xvertext 5.0, Copyright (c) 1993 Alan Richardson (mppa3@uk.ac.sussex.syma)

Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both the copyright notice and this permission notice appear in supporting documentation. All work developed as a consequence of the use of this program should duly acknowledge such use. No representations are made about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

Constellation algorithm is from a paper by Nancy G. Roman, "Identification of a constellation from a position", Publications of the Astronomical Society of the Pacific, Vol. 99, p. 695-699, July 1987. Before 3.6 the figures were the work of Chris Marriot. The list of boundaries is derived from the three files constell.1875.data, constell.1875.hdr and constell.doc at ftp://explorer.arc.nasa.gov/pub/SPACE/FAQ/.

The WCS solver algorithm technique was inspired by a paper by Frank Valdes in PASP, vol 107, page 1119 (1995).

New version of Gemini constellation by Lutz Maendle, lmaendle@csi.com.

Thanks to Dr. Harald Fischer (fischer@vs-ulm.dasa.de) for the GPS awk routine and sample position database.

The high-precision precession routine is from 1989 Astronomical Almanac, as interpreted by Craig Counterman. Mr. Counterman also deserves the credit for providing the initial encouragement to write an astronomical tool specifically for X Windows back in 1990, and for significant assistance while developing the heliocentric models.

The Earth map is derived from data supplied with xearth which included the following notice:

Copyright (C) 1989, 1990, 1993, 1994 Kirk Lauritz Johnson

Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. The author makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

The Earth shaded elevation relief map shipped with XEphem 3.6 is from the National Geophysical Data Center. The one with 3.7.6 is from http://www.shadedrelief.com/world_relief/download.html

The pulsar and Radio databases are based on lists supplied by Robert Payne, rpayne@nrao.edu. Errors in converting to XEphem are mine.

The lunar image is based on one I found surfing at: ftp://seds.lpl.arizona.edu /pub/images/planets/moon/fullmoon.gif. The calculations for the longitude of the terminator and the solar altitude are based on the program colong.bas by David Bruning and Richard Talcott, published in _Astronomy_, October 1995, page 76.

Thanks to Richard Clark (rclark@lpl.arizona.edu) for an improved version of anomaly.c.

A great source of comet information is https://science.nasa.gov/solar-system/comets/

Special thanks to Uwe Bonnes, bon@LTE.E-TECHNIK.uni-erlangen.de, and Ralphe Neill, ran@rdt.monash.edu.au, for their many ideas and support.

Many test cases were gleaned from the pages of Sky and Telescope, (C) Sky Publishing Corp.

Many of the sample cities in the "xephem_sites" file are from the xsat program, which included the following notice:

Copyright 1992 by David A. Curry

Permission to use, copy, modify, distribute, and sell this software and its documentation for any purpose is hereby granted without fee, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. The author makes no representations about the suitability of this software for any purpose. It is provided "as is" without express or implied warranty.

Most of the sample observatories in the "xephem_sites" file are transcribed, with permission, from the table beginning on page 28 in the July 1993 issue of Sky and Telescope. Any errors in transcription are strictly my own.

Thanks to Lowell Observatory and the Minor Planet Center for maintaining their huge lists of asteroids. See https://asteroid.lowell.edu/ and https://cfa-www.harvard.edu/cfa/ps/mpc.html , respectively.

Thanks to the National Space Science Data Center and the Smithsonian Astrophysical Observatory for the SAO star catalogue.

Thanks to the members of the Saguaro Astronomy Club for the preparation and free distribution of their deep-sky database. Any errors in conversion to the .edb format are strictly mine.

Thanks to Chris Beecroft <aldebaransys@home.com> for his encouragement and technical assistance in adding postscript. The limited results in no way reflect on his capabilities. Initial encouragement was also received from Frank M. Siegert <frank@miranda.tue.schwaben.de>. And thanks to everyone who has asked for printing over the years -- I now admit that I like it too!

Bright stars are based on the 5th Revised edition of the Yale Bright Star Catalog, 1991, from ftp://adc.gsfc.nasa.gov/pub/adc/archives/catalogs/5/5050. Common names supplied by Robert Tidd (inp@violet.berkeley.edu) and Alan Paeth (awpaeth@watcgl.waterloo.edu). Any errors in conversion to the .edb format are strictly mine.

I wish to thank all the organizations behind the incredible Internet for its maintenance and free and easy access. I also wish to express my hope that it retains the spirit of cordial cooperation it fostered in its formative years.

I learned most of what I know of X Windows and Motif programming from ICS courses and material found in the various excellent texts from O'Reilly & Associates, Inc.

Thanks to MIT and the X Consortium for inventing, championing and maintaining the X Window system, and the various contributing organizations to the Open Software Foundation for Motif. Their vision of network-aware graphics is still unmatched.

Similarly, I will be forever indebted to all who contributed to UNIX. My passion and appreciation for this remarkable operating system matured while I enjoyed four wonderful years at Kitt Peak National Observatory (now the National Optical Astronomical Observatory), Tucson, AZ, in the early 80's. As with X, UNIX plays a central role in my enjoyment of a career in scientific computing.

It was at KPNO where I met the late Dr. W. Richard Stevens, a fellow champion of the elegance of the UNIX architecture, life-long friend and mentor.

Special thanks to all the folks over the years who have provided innumerable ideas, suggestions and bug reports, both for XEphem and its ancestor, ephem. A major benefit to writing and distributing these programs has been the chance to make many friends from around the world.

Elwood Downey ecdowney@ClearSkyInstitute.com

11.0 Notes

11.1 Horizon

11.2 glob Patterns

11.3 Accuracy

11.4 TODO

• write a tool to find g/k from a set of predicted magnitudes.
• display occultation path between *any* two objects in the Earth view
• add sidereal day and month trail intervals.
• just label month and year tickmarks in trails when they change
• comet tail pointer
• meteor showers, (dedalus)
• Iridium flares
• option for rise/set info to be Today or Next.
• add "Plot JD as date" to plot display
• use better earth shape model
• add T » F and F » T to Binary
• use user-defined horizon for rise/set calculations
• way to repeat the Solver for more solutions, as in "solver in a loop"
• expand .edb to capture real variables
• more hot-keys
• month of lunar phases
• Jup and Sat moon timelines and events, ala S&T
• separate Telescope view window
• connect trails with spline not just line segments
• direct connections to Simbad and NED
• plot in polar coords
• automatic initial Go
• topocentric lunations
• individual control over trails in sol system
• provide a means to save and install multiple color+font schemes.
• tool to generate MPC astrometric report
• draggable eyepieces
• text entry fields to allow higher-precision eyepiece size and PA

11.5 Known Bugs

• Preferences » Time Zone does not update dates of FM/NM if they happen to squirm.
• length of night wrong when savings time causes dusk after midnight
• center constellation names based on boundaries rather than on figures
• solar trails don't account for long-term (10's of years) precession
• plot's View settings are not Saveable.
• figure out calendar prior to Oct 1752.
• Sky View trails are not always clipped properly against a user-defined horizon
• The visual magnitudes for all solar system bodies except the planets do not take into account the phase.
• Changing equinox or geo/topo then update, moon view tables do not update.
• Time not correct when system set to POSIX time
• Earth satellites are not plotted in Sky View correctly in geocentric&altaz mode (use geocentric&radec mode).
  

11.6 History