These Tips let you customize features in CELESTIA to enjoy its best performance!  Learn the tricks which veteran CELESTIA fans employ to create the most exciting voyages, animations and views possible.

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INSTALLATION TIPS

WINDOWS

On a PC computer running the Windows operating system, it is preferable to install CELESTIA in a directory (folder) other than the C:\Programs directory.  For example, first create a directory named C:\Celestia and install CELESTIA there.

FILE ASSOCIATION

When you are installing CELESTIA, you may be prompted with a screen that has check boxes that include:

Associate:    cel://URLs
Associate:    .cel and .celx scripts

If so, make sure that each of these boxes is checkmarked before continuing with the installation.  The first checked box insures that CELESTIA is able to run the exciting  1.6.x and 1.4.1 Links  on this website.  The second allows you to run scripts directly from a File List by double-clicking on the file name.

SAFE CHANGES

The safest way to change certain attributes in CELESTIA requires a.) preserving and renaming any "original" files that control the attributes you wish to change, and then b.) substituting "copies" whose contents can be modified.  This is not difficult, and it insures that you always retain CELESTIA's "original" files in case you make a mistake or later want to undo any of your changes.  The basic steps in preserving and renaming an "original" file, and making a changeable "copy" of it, are as follows.

1. Make a "copy" of the "original" file in its same directory.  (Your operating system will give the "copy" a different name which you will change AFTER Step #2 below.)
2. Rename the "original" file by simply adding the letters ORIG to the end of its 3-letter extension.  (This makes it impossible for CELESTIA to read the "original" file, which is kept in its proper directory if you ever want to revert back to using it.  Note: only the file's "name" has been changed; its "contents" have not been changed.)
3. Rename the "copy" made in Step #1 to the original file's original name.

Now you may make any desired changes to the "copy".  (Remember: never make changes to the "contents" of an "original" file.)  Which files to change and how to change them are described elsewhere on this page.

EASIER-TO-READ TEXT

For  Info Text  and Label Text, CELESTIA's default font has "strokes" that are only one pixel wide.  This makes them hard to read, especially on newer screens that are 1400 or more pixels wide.  Let's see how to make Info Text and Label Text easier to read.

Using the method of making safe changes explained above, we'll change CELESTIA's "original"  celestia.cfg  file.  This file should be found in the main directory in which you installed CELESTIA.

1. Make a "copy" of  celestia.cfg  in its same directory.  (Your operating system will give the "copy" a different name which you will change AFTER Step #2 below.)
2. Rename  celestia.cfg  to  celestia.cfgORIG
3. Rename the "copy" you made to  celestia.cfg

It is now safe to open your new "copy" of  celestia.cfg  in a text editor and change it as follows.  Remember: free text editors like  Notepad2  and  Notepad++  are best for this task as they support UTF-8.

1. Open  celestia.cfg
2. Find the lines that read:
     Font  "sans12.txf"
     LabelFont  "sans12.txf"
3. Change the lines to:
     Font  "sansbold14.txf"
     LabelFont  "sansbold14.txf"
4. Save the file.
5. Restart CELESTIA.

As shown in the comparison below, from now on when you run CELESTIA, your Info Text and Label Text will appear in a bolder, two-pixel-stroke font that is much easier to read than the original default font.

SMOOTHER RINGS AND ORBITS

CELESTIA draws its planetary rings and orbital paths in line segments, rather than actual curves.  The more segments it uses, the smoother the rings (especially Saturn's) and orbital paths will look.  But there's a trade-off here, because the more segments CELESTIA uses to draw these features, the slower it will operate.

To find the most desirable balance between appearance and performance, you might want to try experimenting with changing how smoothly CELESTIA draws rings and orbital paths.  For example, if you want to use CELESTIA to create a movie or a high-resolution picture of Saturn, you may want to temporarily have it draw its planetary rings smoother to obtain the best effect.

How smoothly CELESTIA renders its rings and its orbital paths is controlled in the  celestia.cfg  file.  If you understand and have done the the example above, it is safe for you to open your current "copy" of  celestia.cfg  in a text editor and change it as follows.

1. Open  celestia.cfg
2. Find the lines that read:
     OrbitPathSamplePoints  100
     RingSystemSections  100
3. Change the lines to:
     OrbitPathSamplePoints  200
     RingSystemSections  200
4. Save the file.
5. Restart CELESTIA.

From now on, when you run CELESTIA it will draw its rings and orbital paths twice as smoothly as the default.  Using the same procedure, at any time you can increase or decrease the "appearance vs. performance" smoothness to find the optimum for your computer or for a particular project.

FINDING THE EQUINOXES IN 1.6.x

Note: for an explanation of the concept of the equinoxes,  click here.

When you display the Celestial Sphere in CELESTIA, what you see is the grid for the J2000 epoch, not the continually updated grid for the "equinox of date".  This isn't a bug or an error; rather it is just the same "practical simplification" commonly used when astronomers refer the position of any sky object to the J2000 epoch.

However, this simplification means that, when we see the Sun cross "CELESTIA's" Celestial Equator, we are actually seeing it cross where the "true" Celestial Equator WAS at the beginning of the year 2000!  In reality, Earth's precession makes the "true" Celestial Equator continually "reorient" itself relative to the Ecliptic!  So the further we are from the year 2000 in CELESTIA, the less accurately the Sun's crossings of the program's Celestial Equator will depict the equinoxes.

How much difference is there between the Sun's moving through CELESTIA's (J2000) Celestial Equator and the "true" (of date) one?  It accumulates at roughly 20 minutes per year!  So, on 2010 March 20, the Sun appears to cross CELESTIA's Celestial Equator some 3 hr 20 min AFTER the real Vernal Equinox ()!  Again we stress that this is not a bug or an error in CELESTIA, for its approach too has benefits which make its use common in astronomy.

Fortunately, there are several ways that we can find the equinoxes with good precision in CELESTIA 1.6.x.  For now, we'll offer one method and save others for future months.

This method takes advantage of the fact that CELESTIA provides a way to see the updated plane of the Celestial Equator continually over time.  This is through the use of Earth's Planetographic Grid.  So first click on this  (1.6.x only)  link that shows Earth.

Next Right Click on Earth, then select "Reference Marks" ("Reference Vectors" in ver. 1.6.0), and then select "Show Planetographic Grid".  Now Right Click on Earth again, then select "Reference Marks", and then select "Show Body Axes".  From where we are about to go, this will help you see the Celestia Equator.

Now, the trick is to place yourself "inside" and very near the center of Earth, and then "look out" toward the Sun.  This  (1.6.x only)  link places you only a tiny fraction of a millimeter from Earth's center!  It also tracks the Sun and zooms in on it to an extremely high degree.  By now, you're probably getting the idea of what we're going to do.

To give us a very high accuracy, this next  (1.6.x only)  link turns off CELESTIA's stars, though you can still see a tiny dot representing the Sun's center.  On some computers the Celestial Equator will blink somewhat, but you should get a very good idea of where it is and when the Sun's center crosses it.  You can also see that CELESTIA shows the Sun crossing the Planetographic Celestial Equator within a minute or so of 3:09 UTC, the theoretical Autumnal Equinox time on 2010 September 23!  In addition, you can zoom in even further to get the highest accuracy possible in CELESTIA!

Now, if you click on this  (1.6.x only)  link, you'll see the how far the "true" (of date) Celestial Equator is from CELESTIA's J2000 one!

You can likewise change CELESTIA's time to verify the Sun's similar crossings of the Celestial Equator for other equinoxes.  Whenever you're done, you can click on this  (1.6.x only)  link to take you back "outside" of Earth again.  Don't forget to turn off the Reference Marks you turned on as described above.

Using this technique in version 1.6.x, you'll be able to find equinoxes with a precision of minutes, rather than hours!  And you'll probably also realize that what you can do with CELESTIA is limited only by your own imagination.