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FAQ: Celestia

Table of contents

Installation, Getting started, etc.
  1. Where can I get the most recent version of Celestia?
  2. Where is the documentation?
  3. I have a previous version of Celestia with tons of addons, custom textures, etc. How can I update to the latest version without having to reinstall all of those addons, textures, etc?
  4. I want to see all possible Celestia eye candy. What kind of graphics card should I get?
  5. What changes have been made to Celestia since the last version?
Problems and Bugs
  1. Celestia crashes, what it draws is messed up or it's extremely slow. What can I do? The Moon is purple, blue and red. Why?
  2. Celestia still crashes, draws funny stuff or is extremely slow. What can I do?
  3. Where can I get another version of Celestia that might work better?
  4. Sometimes when Celestia captures an image of its window, there's an ugly bright rectangle in the picture. How can I get rid of it?
  5. Why won't the "Set Simulation Time" menu let me put in a date before 1752?
  6. When I try to capture a picture or movie, the image is stretched out of proportion.
  7. My planet's rings are drawn as a featureless oval. It used to work. What's wrong?
Limitations and unexpected behaviour
  1. Celestia's galaxies are ugly, dim, grey blobs. How can I get colorful galaxies that look like the real things?
  2. A) Why are there no stars beyond about 16,000 light years? B) Why are there no stars in distant galaxies?
  3. Why are my favorite stars not in Celestia?
  4. Sometimes the planets and moons are way far away from where their orbits are drawn. Why?
  5. Why does the illumination level in Celestia not fall off the farther from the Sun I go - surely it should be very dark by the time I get to Pluto?
  6. The Sun and the Moon are much too small in Celestia. What's wrong?
  7. The ISS doesn't appears at the correct position. What's wrong?
  8. Positions on Mars are on the opposite side of the planet or bumps seem to be half a world away from the mountains or it's dark where it should be daylight. Why?
  9. Why are some texture maps upside down and backward? I compared the Celestia textures for Venus, Ida and Miranda with some I found in a book or on the Web, and Celestia's maps are upside down.
  10. Why can't I see Mir or Galileo? I know they're defined in Celestia.
Using and Extending Celestia
  1. How can I make Celestia work like a planetarium? I want to see how the sky should look from my backyard.
  2. I want to write some scripts for Celestia. How can I do it?

Questions and Answers

Question: Where can I get the most recent version of Celestia?
Answer:

Get Celestia v1.3.2 from SourceForge. They have many mirrors for best performance: http://sourceforge.net/project/showfiles.php?group_id=21302

(Oct. 25, 2004: v1.3.2 has been ported to MacOS X !)

Question: Where is the documentation?
Answer:

The primary authors of Celestia spend their time improving the software. Documentation is provided by users. Some have written about specific aspects of Celestia. An introductory User's Guide by Frank Gregorio is available in English.

A translation into French is in progress.

Consider providing a translation into another language yourself.

Links to various versions of the documentatation are on the Web.

Start with http://www.shatters.net/celestia/documentation.html and http://www.celestiamotherlode.net/catalog/documentation.html

Also see http://www.lepp.cornell.edu/~seb/celestia/#2.1.2 for pointers to additional documentation on catalog files (SSC, STC, DSC), planet surface textures, etc.

Question: I have a previous version of Celestia with tons of addons, custom textures, etc. How can I update to the latest version without having to reinstall all of those addons, textures, etc?
Answer:

You can have more than one copy of Celestia on your system at the same time.

Rename the directory (folder) where you have Celestia now, maybe to Celestia131. Verify that things still work: Double-click on the icon for Celestia131\Celestia.exe and look around in your universe.

Install the new copy of Celestia and tell it to use the directory Celestia. It'll create the folder again and install itself there.

Move your Addons at leisure.

Also, please take a look at http://www.lepp.cornell.edu/~seb/addon-intro.html for a description of how to organize your Addons so they can be moved easily.

Question: I want to see all possible Celestia eye candy. What kind of graphics card should I get?
Answer:

a) Only Nvidia FX (5nnn series) and GF (6nnn series) cards with 128MB of memory or more will show all of the eye candy drawn by Celestia v1.3.2.

ATI Radeon 9500 and above, including the X series, are comparable to Nvidia FX 5nnn series cards in functionality, although performance differs. However, not all of the eye candy drawn by Celestia v1.3.2 is compatible with them. This may change in Celestia v1.4.0.

b) Graphics cards with drivers that support only OpenGL v1.4 will show most, but not all, eye candy.

E.g. Nvidia GF4 Ti 4xxx series cards cannot show smooth shadow borders. Also, ATI Radeon cards, even 9500 and better, cannot show haze or smooth shadow borders, but this may change in Celestia v1.4.0.

As of January '05, ATI fixed more of the bugs in the Windows drivers for their lower performance cards, those with model numbers less than 9500, but some features are still missing.

As of October,'04, lockups have been seen on Macs and Linux systems which have any ATI card when drawing bumpmaps and specular reflections. Apparently the lockups are due to bugs in ATI's routine GL_ARB_vertex_program as provided for non-Windows systems. Windows systems with ATI cards and Macs with Nvidia cards don't seem to have these problems.

c) Other cards work, but with various additional limitations.

Some specific limitations:

-- Nvidia MX cards cannot draw shadows of rings on planets, although they can draw shadows of planets on rings.

-- ATI Rage cards cannot show specular highlights or bumpmap shadows

-- textures on Rings, 3D Mesh models, and moving Clouds are limited to the size of your card's texture buffer. This limitation does not apply to the surface textures of spherical planets and moons.

Therefore...:

-- no ATI cards, including the X series, can show surface texture images larger than 2K on a side on Rings, 3D Mesh models, and moving Clouds. Unfortunately, some Addons include 4K textures: Nvidia 4nnn, 5nnn and 6nnn cards have 4K texture buffers.

In order for Celestia to be able to show bumpmap shadows and specular reflections, your card's OpenGL library must support OpenGL v1.4. In particular, it needs to include "GL_ARB_vertex_program".

Starting with Celestia v1.3.2, to draw the best eclipse and ring shadows, your card also must have "GL_ARB_fragment_program" and use floating point to do the graphics calculations. (Celestia v1.3.2 supports these features only on Nvidia FX 5x00 and GF 6x00 cards and not on any others; Celestia v1.4.0 may support these features on ATI 9500 or better.)

As of February, 2004, only Nvidia and ATI have invested the effort in providing OpenGL v1.4. The other graphics chip vendors have not yet upgraded their OpenGL libraries. However, Matrox Parhelia cards seem to have many of the necessary OpenGL v1.4 features in their v1.3 libraries.

Note: The authors of Celestia only have cards with Nvidia graphics chips. Other types of cards sometimes have problems. See Q2 above.

Question: What changes have been made to Celestia since the last version?
Answer:

The developers maintain a list of all new functionality and bug fixes in the Celestia ChangeLog, which is located at SourceForge: http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/celestia/celestia/ChangeLog. Look at the top-most entry in the list, to the right of where it says "Revision #.##", click the "(view)" link to display the most recent ChangeLog.

Question: Celestia crashes, what it draws is messed up or it's extremely slow. What can I do? The Moon is purple, blue and red. Why?
Answer:

Celestia makes use of the most advanced features of OpenGL that your graphics driver claims to support. Many older OpenGL implementations have serious bugs, and so does Apple's OpenGL for ATI cards on MacOS X.

a) Upgrade to the most recent drivers for your graphics card.

Download them for free from the Web site of the manufacturer of your card. Make sure full hardware acceleration is enabled in your display properties.

b) Download and install the most recent version of Celestia. The program is constantly being revised.

c) Workaround: Turn off Celestia's advanced display feature/tell Celestia to ignore specific features that your OpenGL library claims (falsely) to support.

c1) Type a [Ctrl-V] several times to select "Basic" or "Multitexture" render paths instead of the OpenGL Vertex programs.

c2) Edit celestia.cfg. Remove the # that's in front of the line

# IgnoreGLExtensions [ "GL_ARB_vertex_program" ]

(This avoids system lockups experienced under MacOS X 10.3.5 with ATI cards, and purple moons with Intel chips, for example.) Celestia's Help menu lists all of the routines in your OpenGL library. You might consider adding equivalent IgnoreGLExtensions lines for other suspicious routines.

c3) Test: Disable hardware acceleration to verify it's hardware related.

Under Windows, open the "Display Properties" window. Select the "Settings/Advanced/Troubleshoot" tab. (not the "Troubleshoot..." button). Move the "Hardware acceleration" slider all the way to the left. Click on the "OK" buttons to change the settings in use. This will cause Windows to use Microsoft's Generic OpenGL v1.1 library, which is limited and can't show all of Celestia's eye candy, but seems to have relatively few bugs. It does everything in software, works on 2D displays, and is quite slow.

d) Shut down all background programs on your system before running Celestia (i.e., antivirus software, multimedia software such as REAL Player, Musicmatch, etc.) Graphics programs are notorious for consuming system resources and even the best of graphics cards are better off without competing for those resources.

Question: Celestia still crashes, draws funny stuff or is extremely slow. What can I do?
Answer:

Report the exact circumstances and details of your system and graphics hardware and software in the "Celestia Bugs" forum.

For example:

Problem: Celestia crashes when I look at Saturn with Ring Shadows enabled

System: 256MB 1GHz Pentium 4, Windows 98 2nd ed

Graphics: 128MB Radeon 9700, Catalyst 4.1, OpenGL 1.5.4582

Program: Celestia v1.3.2

Hopefully you know the System: information. If you're running Windows, details are usually available in the Control Panel's System Properties menu. Some of the Graphics: information can be found in Celestia's Help menu under "OpenGL Info..."

Question: Where can I get another version of Celestia that might work better?
Answer:

a) Older versions of Celestia are available on SourceForge:

See http://sourceforge.net/project/showfiles.php?group_id=21302 v1.2.4 seems the most robust, but does not include many recent features.

b) Some "prerelease" versions of Celestia for Windows are available on shatters.net: See http://shatters.net/~claurel/celestia/files/

The most recent "prerelease" (e.g. V1.4.0pre6 or later) may work for you, but may be even worse.

Question: Sometimes when Celestia captures an image of its window, there's an ugly bright rectangle in the picture. How can I get rid of it?
Answer:

Sometimes a bright area is recorded where the file requestor menu or any other window overlaps Celestia's main window.

a) This seems to be a bug somehow related to galaxy rendering. Often it will go away if you toggle "Show Galaxies" off and on again before you take your snapshot.

Either use the Render/View Options menu or type the letter "U" twice before you press "F10".

b) Run Celestia in windowed mode, not full-screen. Drag the file requestor away from in front of the main window before you click on "Save".

c) If your graphics card supports it, you can connect a secondary display. Some CRTs are very inexpensive. Drag the file requestor to the other screen.

d) Use an external screen-dump command or program.

Windows includes a "print-screen" command. Under XP, you can use the keyboard combination Ctrl Print-Screen to write the screen image to the clipboard. You can then use any Paint program and Paste the image into it.

If a screenshot captured in Celestia has multiple boxes around it, as if Multiview was on, then this is a bug in Celestia similar to the one above. To make a good clean screenshot image, press [Ctrl + D] before you capture the image. This cancels Multiview.

Question: Why won't the "Set Simulation Time" menu let me put in a date before 1752?
Answer:

March 25, 1752, is when Great Britian and its colonies converted from the Julian calendar to the Gregorian calendar. This changed the day the year changed and also lost 11 days from that year.

The Windows version of Celestia uses Microsoft's date/time input routines. Microsoft didn't want to bother with the complexities of converting between Gregorian and Julian dates. This problem does not exist in the Linux version of Celestia. Chris hopes to replace the Windows "Set Time" routine with a better one in a future release of Celestia.

In the meantime, you can use the "reverse time" keyboard command [J] and the time speedup [L] and slowdown [K] commands to get to the time you want.

Question: When I try to capture a picture or movie, the image is stretched out of proportion.
Answer:

(Thanks to DaveMc for these tips!)

Here are three things you can try...

1. Check the OpenGL anti-aliasing setting of your graphics card. If it is on, try turning it off, or setting it to another option. This seems unrelated to the anti-aliasing setting inside of Celestia.

2. Set your graphics card OpenGL options to "default".

3. Get the most recent drivers for your graphics card.

Question: My planet's rings are drawn as a featureless oval. It used to work. What's wrong?
Answer:

You need to use a smaller ring image, one that is no wider than your graphic card's OpenGL texture buffer. To see how large your OpenGL texture buffer is, use Celestia's menu Help "OpenGL Info"

Older versions of Celestia scaled down large ring texture images so they'd fit into the smaller texture buffer of your OpenGL graphics driver. Celestia v1.3.1 and later(?) no longer do that.

Some older cards, like 3dfx Voodoos, only have a 256 byte buffer. Modern cards have a 4K buffer or larger.

Question: Celestia's galaxies are ugly, dim, grey blobs. How can I get colorful galaxies that look like the real things?
Answer:

The real things are dim, grey blobs. Your eyes are not sensitive to color at the very low light levels emitted by distant galaxies.

( Catalogs of additional dim, grey blobs for use with Celestia v1.3.0 and later can be found at http://www.lns.cornell.edu/~seb/catalogs.html )

Many of the colorful pictures you're used to seeing are enhanced by long exposures on sensitive color film. Others are imaginative "false color" combinations of narrow-band CCD images designed to make visible the specific features of interest to the investigator.

You can add a colorful object to Celestia by creating a 3DS model with appropriate images as surface textures. Define it as a Nebula in a DSC file. Use the Search command in the Celestia "Development" and "Add-On" forums to find examples.

Question: A) Why are there no stars beyond about 16,000 light years? B) Why are there no stars in distant galaxies?
Answer:

A) Hipparcos could only measure parallax to a value of about 1 milli-arc-second.

For details, please read the thread http://shatters.net/forum/viewtopic.php?t=822

B) Celestia currently has technical limitations which prevent it from drawing stars beyond a distance of about 16,000 LY from the sun.

On the second page of the thread mentioned above, at http://shatters.net/forum/viewtopic.php?p=9424, Chris wrote about some of the tradeoffs in the current version of Celestia.

Question: Why are my favorite stars not in Celestia?
Answer:

Celestia comes with only the Hipparcos database of stars with accurately measured distances. They did not measure the distances to dim or variable stars, including close doubles. Someone may have created an Add-on that includes your stars, though. Or consider creating the necessary STC file yourself and contributing it.

For example, see Grant Hutchison's Addon of stars within 25LY at http://www.lepp.cornell.edu/~seb/celestia/hutchison/nearstars.html (This catalog will be included in v1.4.0)

Question: Sometimes the planets and moons are way far away from where their orbits are drawn. Why?
Answer:

To draw the orbits, Celestia only calculates 100 or so precise locations and then draws straight lines between them. If the orbiting body doesn't happen to be close to one of those 100 points, then it won't be very close to the line, either. The position of the orbiting body is calculated very accurately. The lines aren't.

Celestia only calculates a few points around the orbit in order to minimize the amount of computation needed between frames. The more calculations are required, the slower the frame rate is.

Starting with Celestia v1.3.2, you can specify the number of segments in an orbit track. Use your favorite text editor to modify the file celestia.cfg. Change the line

OrbitPathSamplePoints 100
Question: Why does the illumination level in Celestia not fall off the farther from the Sun I go - surely it should be very dark by the time I get to Pluto?
Answer:

The human eye can adapt to a very wide range of illuminations, so it wouldn't be as dark out there as you think - about the level of moderate indoor lighting, in which you can see very well. At the other end of the scale, your computer monitor is physically incapable of generating the brightness of illumination that pertains on the inner planets. Fortunately it doesn't need to, since all that would happen would be that your pupils would constrict to reduce the incoming light to a more comfortable level.

So in summary - a) There's no way Celestia can display "realistic" brightnesses on your computer screen; but b) such "realism" is unnecessary because your eyes merely adapt to compensate.

Question: The Sun and the Moon are much too small in Celestia. What's wrong?
Answer:

Their diameters are exactly right. As seen from the earth, they are both about a half-degree across. Celestia's window is about 45 degrees across, so the Sun and Moon are about 1% of that. They are drawn only 10 pixels wide if your screen is 1024x768.

Remember that your computer screen is only about 10-20 degrees wide in your own field of view. Celestia's 45 degree field provides a "wide angle" view of the sky. This makes objects look smaller than you might expect.

The apparent large size of the Sun and Moon as we see them in the sky is a psychological illusion. There are several different explanations for this. If you take a picture of the moon with a camera lens that has the same field of view as Celestia, you may be surprised at the small size of its image.

At least one book has been written about this effect:

The Mystery of the Moon Illusion:

Exploring Size Perception

By Helen Ross and Cornelis Plug

Here's a review: http://www.astronomyedinburgh.org/publications/journals/46/moonillusion

Here's a simple experiment suggested by "HarrieS", a guest on the Celestia forum:

Here is something you might try: a finger at arm's length is about two degrees wide for most people. That means that you can fit four moons side by side. Go outside and check it. Now have a direct look at your finger indoors. Can you still believe that four moons will fit on it?

But if your head is positioned e.g. 70 cm away from your e.g. 17" monitor, which measures 32 cm across (at least mine does), then the effective field of view looking at the Celestia sky "through" your monitor screen is 2*arctan((32/2)/70)) ~ 26 ?. Hence, if you decrease the Celestia field-of-view to 26? you may get a more accurate appearence of what you would see looking out the window.

Question: The ISS doesn't appears at the correct position. What's wrong?
Answer:

The orbit of the ISS changes continuously in ways that are almost impossible to predict due to things like atmospheric drag, light pressure, cargo ship docking, etc. If you want an accurate orbit, you'll have to update it on a daily basis.

ISS TLEs (Two Line Elements) are posted to the AMSAT SAREX mailing list regularly by "Dave Larsen PhD". See http://www.amsat.org/amsat/archive/sarex/31day/threads.html

Here are the ISS TLE orbital parameters for August 16th, 2004:

ISS 1 25544U 98067A 04229.23839543 .00019757 00000-0 15906-3 0 4532 2 25544 51.6323 19.1941 0005251 117.9988 304.8582 15.70921896327755

Grant Hutchison has provided a spreadsheet to convert TLEs into Celestia SSCs at http://www.lepp.cornell.edu/~seb/celestia/hutchison/spreadsheets.html#2

Also, don't forget that Celestia models the shape of the Earth using a spheroid. The actual shape of our planet is much more complicated. As a result, a view from the Earth's surface in Celestia is not accurate enough to show the correct path across the sky of satellites in low Earth orbit like the ISS. In other words, you can't use Celestia to find out where to look in the sky to see the ISS.

Question: Positions on Mars are on the opposite side of the planet or bumps seem to be half a world away from the mountains or it's dark where it should be daylight. Why?
Answer:

You have a misaligned map. Celestia requires that all maps have 0 degrees of longitude in the center, with 180 degrees of longitude at the edges. All of the surface texture image maps of all of the moons and planets that come with Celestia have this alignment.

In contrast, many maps of Mars were created with 0 degrees of longitude at the left and right edges, and with 180 degrees of longitude in the center. This includes the maps on www.shatters.net in Fridger's "Texture Foundry".

Using a map with 0 at the edge would cause the symptoms you describe. You need to cut the map in half and exchange the halves or you need to find a map that's properly aligned.

Question: Why are some texture maps upside down and backward? I compared the Celestia textures for Venus, Ida and Miranda with some I found in a book or on the Web, and Celestia's maps are upside down.
Answer:

Many sources for planetary maps (such as the USGS) use a mapping convention called "ecliptic north" - the north pole of any planet or asteroid is defined as being whichever rotational pole points north of the plane of the ecliptic (the plane of the Earth's orbit around the Sun). Each planet or asteroid can then be classified as a "direct" rotator, if it rotates in the same direction as the Earth when observed from above its north pole (ie counterclockwise); or as a "retrograde" rotator, if it rotates in the opposite direction.

In contrast, Celestia uses an equally valid mapping convention called "rotational north" - north is defined as being the pole around which the planet appears to rotate counterclockwise, irrespective of that pole's orientation relative to the ecliptic.

For direct rotators, this difference is irrelevant - "north" turns out to be the same direction in both mapping conventions. But for retrograde rotators, Celestia's north pole corresponds to ecliptic south - so you will find many maps of retrograde rotators like Venus, Ida and the moons of Uranus that appear to be upside down relative to those in Celestia. If you want to convert such maps for use in Celestia, you'll have to turn them through 180 degrees.

Question: Why can't I see Mir or Galileo? I know they're defined in Celestia.
Answer:

Set Celestia's simulation time to be when the spacecraft was in orbit. Celestia does not display spacecraft if they are not in orbit at the time of the simulation.

For example, Mir was launched on February 20, 1986, and reentered the Earth's atmosphere on March 23, 2001, at 05:55 GMT. Celestia will show Mir only if you set the time to be somewhere between those two dates.

This is controlled by Beginning and Ending directives in the definition of Mir in solarsys.ssc. If you remove those statements, Celestia will always draw Mir in orbit.

Question: How can I make Celestia work like a planetarium? I want to see how the sky should look from my backyard.
Answer:

If you're running Celestia v1.3.0 or later

0) Select the body from which to observe; the Earth maybe Smile

1) use the GoTo menu to specify your Longitude and Latitude and GoTo there

2) type a y = Sync Orbit

Under Windows:

3) type a Ctrl-G = GotoSurface

4) type a Ctrl-F = change Arrow keys to AltAzimuth mode

Under Linux:

3) type an Alt-S = GotoSurface

4) type an Alt-F = change Arrow keys to AltAzimuth mode

Unfortunately, there is not (yet) an alt-az coordinate system display, but typing a ; will turn on the equatorial coordinate system display.

Alternatively, if the version of Celestia that you're using includes Lua, you can use Harald Schmidt's "Show Azimuth and Elevation" script at http://celestia.h-schmidt.net/ (The Windows version of Celestia includes Lua, but Mac versions and some Linux versions don't.)

Question: I want to write some scripts for Celestia. How can I do it?
Answer:

There are two scripting languages available. The first - known as CEL-Scripting - is a very simple scripting language of its own which understands commands like "go here, look there, set flag, display text". These commands should go into a file with the filetype .CEL

The second, newer (available starting with Celestia 1.3.1) language is known as CELX or Lua-scripting is a complete programming language, i.e. including functions, variables, loops etc. See here for details about Lua: http://www.lua.org/

For documentation see: http://www.celestiamotherlode.net/catalog/documentation.html, http://www.lns.cornell.edu/~seb/celestia/celestia_notes.html#4.0

For scripts see: http://www.celestiamotherlode.net/catalog/scripts.php

(As of Celestia v1.3.1, scripts may be in any folder. Previously they had to be in Celestia's "root" folder.)

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