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When reading a TLE entry, XEphem assigns the valid range of dates for a set ofelements to the greater of 100 days or the time required for the mean motionto change by one percent either side of the element epoch.
7.2 IndexThiswindow shows a list of all objects currently loaded into memory sortedby name. Or, by chosing a toggle button across the top, the list canbe restricted to just deep sky, stellar, binary systems, solar systemandEarthsatellites. The list does not include Favorites.

Each object name, including all alternate names, are in the scrolledlist onthe right. Clicking an arrowbutton moves the list by one object up or down; clicking above or belowthe thumbcontrol scrolls the list so that the top object moves to the bottom or visa versa. Clicking on an objectdisplays its defining parameters in the box to the left, and alsodisplays its .edb file format entry in the read-only text field below.

The list of objects may be searched by entering a glob pattern in the Search field thentyping Enter or clicking Search. If more than one object name matches,clicking Search again scrolls to the next candidate; the search wrapsback to the front when no more are found.

Buttons across the bottom function as follows:

Sky Point

This will mark the object currently selected in the SkyView, repointing if necessary to move it into the field ofview.

Show in Gallery

If this object is in the Gallery, this button will be available and willdisplay the object.
Save as Favorite

This button will add the objectcurrentlyselected to the list of Favorites.
Tel Goto

This will send the object currentlyselected to the Telescope controlsystem. Whether this button is active depends on the state of thetelescope control subsystem when the Index window was opened. If thebutton state is incorrect, close and reopen the Index window. 7.3 FavoritesThiswindow allows you to add, arrange, remove and temporarily deactivate anarbitrary collectionof XEphem objects, called Favorites. Once defined as a Favorite, theobject remains available whether or not its original database file is currently loaded.

Favorites have special significance in several places throughoutXEphem. For example the rows in the Data Tableand in the Night at a Glance windows areexactly those of the Favorites. The Earth viewshows those Favorites which are satellites. Favorites are availableveryeasily in the Favorites menu in the Sky View.And the Solar System view displays thoseFavoritesthat are within the solar system.

Objects may be added to the list of Favorites in several ways:

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

Each entry in the Favorites list shows its complete .edb formatdefinition. Each entry has the following controls:
Del
removes the entry from the Favoriteslist

Up and Down arrow buttons

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

Use

specifies whether to use or hide theentry fromthe rest of XEphem without actually Deleting it. The buttons across the bottom allow you to Save the current setof Favorites to a file and later Load them again.The suffix of these files must be .fav and will be addedautomatically if not included in the file named in the text field. WhenXEphem first starts, it automaticallyloads the file named in the Save text field. To save this file name, goto Preferences Saveand Savethe XEphem*Favorites*File resource under the Favorites category.


7.4 Download
Thiswindow provides an easy means to download from the Internet to disk andsimultaneouslyload into memory any file which contains objects defined in eitherXEphem's .edb format or the NORAD 2-Line Element (TLE) format commonlyused for Earth satellite. The file is saved in the Private directory, converted to .edbformat if it is not already.

Several particularly useful sites as of this build are already entered.The first five are from Dr. TS Kelso's Earth satellite lists at celestrak.org. The other four arethe Minor Planet Center's lists of hot comets and unusual asteroidsspecially formatted for XEphem.Click Get beside the desiredcatalog to download the file to the Private directory andsimultaneously load into XEphem memory.

Special files created by the Minor Planet Centerand LowellObservatory may also be downloaded. Each organization maintainsextensive lists of all known asteroids and produces on a regular basisKeplarian orbital elements precessed to the current date. Both are ofexcellent quality. When the Getbutton is clicked, XEphem downloads the appropriate file, uncompressesit, reformats it to .edb format and splits the results into two filesfor convenience. One file will contain all asteroids which can everbecome brighter than magnitude 13, and the other (with a "_dim" suffix)contains all the rest. All files are created in the user's PrivateXEphem directory. The real work is performed by two perl scripts,mpcorb2edb.pl and astorb2edb.pl, respectively. These may be run independentlyof XEphem if desired.

7.5 Field Stars This window allows you to controlwhichfield starsources you wish to use. The window is accessible from the Main windowas well as from the Control menus of most graphical views.

XEphem uses the term "field star" to refer to the huge numbers of faintstars visible in any real world view of the sky. Field stars aregenerally far more numerous than could be reasonably accommodated inthe XEphem *.edb database format. For this reason they are stored andmade available in their own special compact forms for utmostefficiency. The downside to this approach is that field stars are notincluded in the totals presented by the Data Files window norare they available for searching or inspection using the Data Index window.This results in little loss of generality, however, since (oncefound!) they may be assigned to the user Favorites.

The controls in the Field Stars setup window are grouped intocategories, depending on the basic source of the stars, as follows:

7.5.1 Hubble GSCThe Hubble Guide Star Catalog is a seminal work created by the SpaceTelescope Science Institute to support the Hubble Space telescope. Itcontains from 13 million unique stars, or about 300 stars per squaredegree of sky.

ASP CDROM Directory

This choice enables reading field starsfrom the Hubble Guide Star Catalog made available some years agoon two CDROMs published by the Astronomical Society of thePacific. Mount a CDROM somewhere onto your filesystem, type thename of the mount directory in the text field provided then turnthis option on and press Apply. Note that XEphem assumes your CDROMdriver removes the trailing ";1" from all filenames.

Local Cache Directory

This choice enables reading GSC fieldstars from your local disk. If this option is on along with theCDROM option, then as requests are satisfied from the CDROM acompact form of the same data will be written to files below thedirectory named in this option. Then the next time the same field starsare needed, and this option is on, they will be obtained from thelocal disk files rather than the CDROM. In fact, the CDROM is notneededor used if the local disk contains all the stars for any givenaccess. The entire 2 CDROM set loads onto disk in this format insome 180 MB. The default path of the directory which holds thedisk version is "catalogs/gsc" off the Shared directory. Note:There is also a utility in the tools/gsc directory, gscload, withwhich you may preload any entire CDROM segment at once if desired.These files are already included in te commercial version ofXEphem.

Internet to xephemdbd

This choice is to use the Internet toaccess an XEphem GSC server. To use this source, select thisoption and type the URL to the remote xephemdbd.pl in the textfield provided.

GSC 2.2 Directory

This choice enables using a local copyof the GSC 2.2.0.1 catalog in xe3 format. This catalog only containsstars between magnitude 10 and 18.5, so it must be used in conjunctionwithan additional catalog for completeness. The Hipparcos catalog is anideal companion and is automatically chosen as a convenience.

7.5.2 USNO A or SA catalogs
Root directory

This choice of field stars supports the SA and the A series ofastrometric catalogs produced by the US Naval Observatory. The SA2.0for example, includes some 54 million stars, about a tenth of the parent A2.0,spatially sampled so there is about 1,300 stars per square degree ofsky. Note that such a uniform distribution does not "look" much likethe real sky, but it is great for its intended use as an astrometricmesh for comet hunters or such. If you have such a catalog, simplyenter the name of its base directory and toggle this switch on.The default assumes a symbolic link, "catalogs/usno" off the shareddirectory. Multiple versions of the catalogs can be stored, each inits own directory, but only one may be active at a time.

The suggested citation for SA2.0 follows:

Monet, D., Bird, A., Canzian, B.,Dahn, C., Guetter, H., Harris, H., Henden, A., Levine, S., Luginbuhl, C.,Monet, A., Rhodes, A., Riepe, B., Sell, S., Stone, R., Vrba, F., Walker, R.,1998, USNO-SA2.0, (U.S. Naval Observatory, Washington DC).
This catalog has been included with permission of USNO as long aswe mention the following stipulations:

It may not be the latest version,check with
If you paid for XEphem, you paid forthe software, not this catalog. The catalog is available free fromthe USNO.
Inclusion of the SA2.0 catalog doesnot imply an endorsement of XEphem by USNO; nor was there privilegedaccess to the catalog; nor does the US Government affirm orguarantee that XEphem works properly in any way.
7.5.3 Proper Motion catalogs
These large catalogs include information regarding proper motion.Two such catalogs are currently available ready for XEphem. You mayonly use one at a time, by choosing the corresponding toggle

PPM catalog

This is the Positions and Proper Motioncatalog of S. Roeser and U. Bastian, AstronomischesRechen-Institut, Heidelberg, published in 1990. The PPM includes468,586 stars rather evenly distributed throughout bothhemispheres. This averages out to more than 10 stars per squaredegree. The set here includes the original North and Southeditions plus the extended supplement. The set includes more than99% of the stars in the original SAO catalog and some 70% of theHenry Draper Catalogue (HD). While the SAO catalog is more or lesscomplete to V=9, with stars as faint as V=10, the PPM catalog isfairly complete to V=9.5, and goes somewhat deeper than V=10.

Hipparcos and Tycho-2

This catalog is a combination of theHipparcos and the Tycho-2 astrometric catalogs published by theEuropean Space Agency. This catalog contains all Hipparcos starsfor which astrometric and magnitude values are assigned, and alladditional non-redundant entries from the Tycho-2 catalog exceptmultiple-component entries. There is a total of some 2.5 millionstars, or about 60 stars per square degree. One example of a star withhigh proper motion is Groombridge 1830 (HD 103095), in Ursa Major,near 11h53m 37d44m. For a nice discussion see Burnham's CelestialHandbook, Volume III, page 1978. By comparing its position in eitherPM catalog with the same entry from the GSC one can deduce thisparticular GSC field was evidently taken in early 1983.

UCAC
This choice allows using the USNO Astrographic catalog with XEphem. Formore information on this catalog please refer tohere.As of release UCAC4, the directory specified must be that which containsthe u4b and u4i directories. In turn, u4b must contain all 900 z files andu4i must contain u4index.unf and u4hpm.dat.
7.5.4 Skip likely duplicatesAll of the above may be used together with the regular databasefacility of XEphem. If this option is on, XEphem eliminates whatappears to be redundant entries for the same star from the variouscatalogs. Two stars are considered the same if their positions matchwithin the given number of arcseconds and their brightnesses differ byless than the given number of magnitudes. (The generous defaultmagnitude tolerance is because the GSC and the PPM use varyingfilters).

When deciding on the final selection for such duplicate entries thehighest priority is the local database, then the HD or SAO entry,then the PPM entry, then Hipparcos, then Tycho and finally the GSCentry.When you have made the desired entries, pressing Apply will attempt to check eachfilename, directory and Internet choice, as appropriate. The cursorwill be a Watch while the tests are in progress. If something does notseem correct, a warning window will appear and the option will beturned back off. If everything seems to be operating correctly, youare in business. The Ok buttondoes the same thing but then also closes the window if they allsucceed.

7.5.5 NotesIf at any time something goes wrong during the acquisition of anyField Stars from any View, the responsible option in that view is alsoturned off automatically. The problem should be corrected and Fieldstars turned on again.

All field star sources will silently enforce limits on the total numberof stars they yield for any query. As of this writing, local queriesexcept USNO are limited to 30 degrees; USNO are limited to 15 degrees;network queries impose various limits.

8.0 Preferences
The simple choice preferences are covered in the Main Window section.See Preferences menu,
8.1 Fonts Thiswindow lets you change most of the fonts used by XEphem. The basictechnique is to specify a font, use the four toggle buttons to choosewhich action to take then perform the action in a particular fontcontext by clicking in the menus accessed from the menubar across thetop.
To browse the available fonts, type a pattern in the field provided andclick Search. This willdisplaythe names of all fonts matching a pattern. To see all available fonts,use the wild card pattern of a single star (*). To be more specific,specify the fields desired and fill the gaps between with the starwildcard. See the next section for a description of each field.

Clicking a font in the top list will display a sample and its full namein the region at the bottom.

The Buttons, Text and Other menus in the menu bar acrossthe top provide ways of referring to several font contexts. The fourtoggle buttons just below the menu bar determines what happens when oneof these context menu buttons is clicked, as follows:

Get current

When this toggle is active, clicking acontext menu button will cause the name of the current font for thatcontext to be displayed in the pattern field and history list.
Get default

When this toggle is active, clicking acontext menu button will cause the name of the last saved defaultfont for that context to be displayed in the pattern field andhistory list.
Set

When this toggle is active, clicking acontext menu button will cause the font named in the pattern fieldof this window to be applied to that context throughout XEphem.
Restore default

When this toggle is active, clicking acontext menu button will cause its last saved font value to bereinstated through XEphem.
Fonts that have been changed from their default values are tagged inthe Preferences Savewindow (when opened or after you do a Refresh). This allows you to Savethe new fonts set here permanently. If you do not Save it, the changeonly effects XEphem until you exit.

There are a few situations scattered around within XEphem for whichchanging fonts at runtime from this window does not work perfectly.For example, changing to a smaller font does not shrink some windowsas much as you might expect. Such anomalies are known challenges anddo not indicate serious problems. After Saving the fonts andrestarting XEphem, all will work again as expected.
8.1.1 XLFDThe font names are in the format called X Logical Font Description.There are 15 fields separated by hyphens. The fields are as follows:

Foundry

The organization that digitized the font data.Family
The commercial name of the font.Weight
The relative weight of the font, such as bold, medium or regular.
Slant
A code indicating the slant: r Roman (no slant)
i Italic (slant left)
o Oblique (slant left)
Set Width
The width with respect to what the foundry considered normal.Choices include normal, condensed, narrow, double.Additional Style
Anything else needed to uniquely identify the font, such as sansor serif.
Pixel Size
The height of an em inpixels.Point Size
The height of an em intenths of a point, where one point is 1/72 inch.Horizontal Resolution
Vertical Resolutoin
The resolution of the device for which the font was designed, inpixels-per-inch.Spacing
A code indicating the spacing between characters in the font: M Monospaced (fixed pitch)
P Proportional spaced (variable pitch)
C Character cell (each character occupies the same size box)

Average Width
Average width of all characters in the font, measured in tenthsofa pixel.Registry
Enoding
The registration authority and their name for the character setfrom which the characters in the font are drawn. For example ISO8859-1,also known as Latin-1.Scalable fonts are indicated by 0 for point size, pixel size, x and yresolution and average width (fields 7, 8, 9, 10 and 12). To choose aspecific scalable font, specify desired values for some but not all ofthese fields, letting the system fill in the others.
8.2 ColorsThis window lets you change most of thecolors used by XEphem. The basic technique is to use the four togglebuttons to choose which action to take then perform the action in aparticular color context by clicking in the menus accessed from themenubar across the top.

The possible actions are as follows:

Get current

When this toggle is active, clicking acolor context menu button will cause the current color for thatcontext to be displayed in the color patch in the lower right cornerof this window.
Get default

When this toggle is active, clicking acolor context menu button will cause the last saved default colorfor that context to be displayed in the color patch in the lowerright corner of this window.
Set

When this toggle is active, clicking acolor context menu button will cause the color currently beingdisplayed in the color patch of this window to be applied to thatcontext throughout in XEphem.
Restore default

When this toggle is active, clicking acolor context menu button will cause its last saved color to bereinstated.
Above the color patch are three sliding scales that allow you to definea color using either Red+Green+Blue or Hue+Saturation+Value, dependingon the toggle. Each scale ranges from 0 through 255. Hue is the basicspectral color, where 0 is red, 85 is green, 170 is blue. Saturationis the amount of color purity, where lower values mix in more white.Value is like brightness, where 0 is totally black.

The text field at lower left allows you to type a color using one ofthe standard descriptive names, such as "steel blue", or in hex RGBnotation, for example #ff0000 for pure red, #00ff00 for pure green#0000ff for pure blue. After typing the desired value, press Enter toset the scales and see the color in the patch. This field is also setautomatically when the scales are used to set a color, during Grabbing(see next), and when a color context is retrieved.

The history list in the lower left stores each color name that is usedfrom the name field, making it easier to reuse a color. Selecting anamewill copy it to the name field and show it in the color patch. You canselect history entries with the mouse, or by browsing with the Up andDown keyboard arrow keys.

8.2.1 Colors Control menu
Nightmode

This changes the XEphem background toblack, and uses the Night vision color for all text. Clicking thisback off will restore the previous colors. Note that when Night visionis on, you may not change the colors it effects. This is to eliminateconfusion with regards to whether or not they are new in the Savewindow.

Grabcolor

Press this button and the cursor willchange to a crosshair. Move the cursor around on the screen and thecolor of the pixel under the crosshair will be displayed; pressButton1 to capture the color and resume normal cursor operation.

Clearhistory

Erases all entries in the History list.


When a color context is changed, it also changes the correspondingresource. In the Preferences Save window you will notice that the resource becomesmarked as Modified (when opened or after you do a Refresh). Thisallows you to Save the new color choice permanently. If you do notSave it, the change only effects XEphem until you exit.

8.2.2 Star colorsXEphem assigns colors to stars based on their spectral classification.The default colors were chosen based on work done by Mitchell Charity.The colors are specified using X Resources. The resource names eachbegin with "XEphem.starSpect" followed by one or two characters. Thevalue of the resource is the color. The following table shows thedefault spectral color resources built into XEphem:


XEphem Resource Name
Default Color Value
XEphem.starSpectO #9bb0ff XEphem.starSpectB #aabfff XEphem.starSpectA #cad7ff XEphem.starSpectF #f8f7ff XEphem.starSpectG #fff4ea XEphem.starSpectK #ffd2a1 XEphem.starSpectM #ffcc6f XEphem.starSpectN #ff8f2c XEphem.starSpectS #ffc574 XEphem.starSpectC #ff9e40 XEphem.starSpectT #ffd19a XEphem.starSpectW #c4c4ff

XEphem uses the closest entry with matching first character. If noentry is found with matching first character then white is used and amessage is added to the System log. Thespectral color resource values may be edited or additional resourcescanbe added but this must be done by hand, there is no GUI supportavailable. Always edit the XEphem resource file while XEphem is not running to avoid any chance ofconflict.
8.3 SaveThis window displays all of theoptions,settings and controls, collectively called Preferences, throughoutXEphem that may be saved andreinstated next time the program is started. XEphem has many suchpreferences, sothey are separated into categories in this window for easiermanagement. Each category may be expanded or collapsed using the+/- toggle square to show each individual preference.

Preferences are saved using the standard Resource mechanism provided bythe X Window System. These resources are saved in the file XEphemlocated in the Private directory.

Each preference may be tagged for saving. The toggle at the topcontrols whether all tagged preferences will be Autoatically savedwhen XEphem is Quit.

Preferences have been divided into two classes.
Major: In the opinion of the author thesepreferences are sufficiently interesting that they are likely to beworth saving and automatically restoring between one invocation ofXEphem and the next.

Minor: Everything else, presumably less critical in nature. Itis expected that you are likely tochange these preferences frequently in due course while operatingXEphem yet they do not cause major effects on program behavior sosaving them atany one particular setting is not especially compelling. Minorpreferences are things like window size and position, scale settingswhichonly effect views, and all of the Sky View Filter and Option settings.

This distinction is of course rather arbitrary so please takecare when changing and saving preferences so the ones you want aresaved.
The number of preferences in each class currently taggedfor saving is indicated by messages near the top.
The scrolled area can display each preference, whether it is tagged forsaving and the ability to change whether it is tagged. Each category ofpreference can be expanded for more detail using the +/- toggle square.
In the expanded view, each preference and its value areshown exactlyas it will appear in the disk file if Saved. Those preferenceswhich differ from the last time they were Saved, or since XEphem wasstarted if no Save has yet occurred, are marked with a bullet. Majorpreferences are marked with a solid bullet, Minor preferences with anhollowbullet. A toggle next to each preference allows individual selectionover whether the preference will be written to disk on the next Save.After each Refresh, the toggles are set for those preferences found tohave changed since the last Save if their class is set to beautomatically tagged. Each toggle may be changed manually in eitherdirection to override this automatic behavior on an individual basisif desired but not these will be overridden with the next Refresh.

In the collapsed view, if at least one Major preference is out of datein a category, a solid bullet is placed next to the category heading;otherwise if at least one Minor preference is out of date a hollowbullet is used.
Note that the information in this window does notautomatically track changes in preferences as XEphem is used. You mustuse Refresh to update the status manually when desired. In particular,the values which are Saved are what they were the last time Refreshwas performed, not what they actually are at the moment Save isactivated.

Save now

Write each tagged preference to disk tothe XEphem resource file.If the file already exists, it will first be copied to XEphem.bak inthe same directory. If a preference already exists in the file it willbeedited in-place, otherwise a new entry is added at the bottom. Otherlines in the file are left unchanged. After using Save, all preferenceswill be considered up to date, even if they were not selected to bewritten to the preference file.
N.B. The values saved are as theyappear in this window, which may be different from their currentvalue if they have changed since the last Refresh.
Refresh

Update the changed and save status ofeach preference. This refresh action alsohappens automatically after a Save is performed and just beforeXEphem quits when deciding which preferences to save if the Automaticsaving option is enabled. 9.0 Multifunction ToolsThe tools in this section are used in several different placesthroughout XEphem. The descriptions here are generic. If there are anyspecial issues when used in certain contexts they will be described inthe appropriate sections elsewhere.
9.1 Trails Thiswindow allows you to define a set of time values spaced at regularintervals before and after the current XEphem time and define whichand in what manner values will be annotated with a time stamp.

This is a general purpose facility used in several places throughoutXEphem, generally for the purpose of establishing a trail of objectmotion. This description will be of a general nature.

Six format parameters must be specified:

Orientation

This choice determines where thestampsappear in relation to their corresponding position mark. The firstseveral options should be self-explanatory. The last two, Path-left andPath-right, cause the time stampsto be placed to the left or right side of the trail path, as one wouldperceive these directions when traversed in forward time order. Inno case are the time stamps ever drawn to require you to turn yourhead more than 90 degrees left or right.
Interval

This is the time interval between eachstep. Choose from among several predefined intervals or choose Customand enter any desired intervalin the space provided. It is okay to specify more than 24 hours toachieve intervals of several days. It is also okay to specify negativevalues to run time backwards.
Label

This choice determines which intervalswill to be labeled with a time stamp. Choose from among severaloptions or choose None if no labelingis desired. Times will be printed surrounded by parentheses if theobject is an Earth satellite and it is eclipsed.
Format

This choice determines the format inwhich to displayeach time-stamp. Choose Hour:Minutewith or without Seconds or the date formatted as per the Preferences Date formatsoption in the Main menubar, see Preferences.
Font

This choice sets the size of theannotation text font.
Start

This choice specifies how the firsttime value is derived from the current XEphem time. The lower rightradio box offers several methods of determining the beginning of thefirst time interval. The idea here is generally to match the timevalues of each time mark with the precision implied by the format, butto allow other options for special situations.

Whole min rounds the currentXEphem time forward to the next whole minute, if necessary;
Whole day rounds to the nextwhole day.
Whole interval rounds to thenext whole multiple of whatever time interval is set (as specifiedin the Intervals choices).
Now means to begin with thecurrent XEphem time without any initial changes.
Two scales near the bottom specify the number of tick marks to createbefore and