A preliminary Celestia User's FAQ

[selden]

Here's a start at a User's FAQ.
If you have suggestions for new Q/As, please post to the Celestia Users Forum, with a subject of "FAQ". I'll insert your suggestion into this thread.

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Here are the answers to Q0-Q6.
Links to additional FAQs are below #6.

Q0: Where's Celestia?
Q1: Why does it crash?
Q2: How to report a problem?
Q3: Where's a better version?
Q4: What graphics card?
Q5: Why are some stars missing?
Q6: Where's the documentation?
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Q0:
Where can I get the most recent version of Celestia?

A0:
Get the most recent Celestia installation file from SourceForge. They have many mirrors for best performance:
http://sourceforge.net/project/showfiles.php?group_id=21302

Q1:
Celestia crashes, what it draws is messed up or it's extremely slow. What can I do?

A1:
Celestia makes use of the most advanced features of OpenGL that the graphics driver claims to support. Unfortunately, many OpenGL implementations have serious bugs in the new code for those advanced features.

Therefore, the very first thing to do is to

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

==========

For PCs running Windows with plugin graphics cards, you can download the drivers for free from the Web site of the manufacturer of your graphics card. Make sure full hardware acceleration is enabled in your display properties.

For laptops and desktops running Windows with embeded graphics chipsets, you usually must download the most recent drivers from the Web site of the manufacturer of your computer. Sometimes generic drivers are available from the manufacturer of the graphics chipset.

Be sure to use the following procedure when installing new graphics drivers:

0. download driver installation program
1. use the Control Panel / Add or Remove Programs menu to delete the current graphics drivers.
2. Reboot
3. Cancel out of XP's offer to install new drivers.
4. Run the Installation program for the new drivers.
5. Reboot
6. Configure desktop resolution and other desirable features.

The two reboots are essential in order to cause the old low-level drivers to be deleted. Without those reboots, the old low-level drivers will not be deleted and the new installation will not work properly, although it may not generate any error messages.

==========

For Apple PPC and Intel computers running MacOS X, you must upgrade to the most recent version of the operating system. Updated drivers usually are not available separately.

Apple's OpenGL on MacOS X often has serious bugs which sometimes are not fixed in the most recent release of MacOS. You must report those problems to Apple, otherwise they will not get fixed.

==========

For computers running Linux, you usually can download the drivers for free from the Web site of the manufacturer of your graphics card.

ATI's fglrx drivers for Linux often have serious bugs. Try to use the driver shipped with the most recent version of Xorg's X server software.

==========

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


c) Workaround: Turn off Celestia's advanced display features.

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

Workaround: tell Celestia to ignore specific features that your OpenGL library claims (falsely) to support.
To do this, edit celestia.cfg. Remove the # that's in front of the line

Code: Select all

# 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. Intel chips don't have support for some of the graphics routines used by Celestia v1.3.2 and earlier. A workaround has been included in Celestia v1.4.0 and later.)

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 even works on 2D displays, but it draws everything using software and so is quite slow.

See also: Addendum to A1


Q1.c2
The Moon is purple, blue and red. Why?
A1.c2
Your computer's OpenGL driver is buggy. It doesn't draw bumpmaps correctly.

Solution: install an updated graphics driver or try the workarounds described above.
=================================================

Q2:
Celestia still crashes, draws funny stuff or is extremely slow. What can I do?


A2:
Report the exact circumstances and details of your system, 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 v1.4.1

Hopefully you know the Sytem: 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..."

If you're running Windows, more details can be found in the Control Panel's Display Properties menu.

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Q3:
Where can I get another version of Celestia that might work better?

A3:
a) A few older versions of Celestia are available on SourceForge:
See http://sourceforge.net/project/showfile ... p_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://www.shatters.net/celestia/files/
The most recent "prerelease" (e.g. V1.5.0pre3 or later) may work for you, but may be even worse.

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Q4:
I want to see all possible Celestia eye candy.
What kind of graphics card should I get?

A4:
a) Only Nvidia 5000 series or greater (e.g. 6000, 7000, 8000, 9000, 250) cards with 128MB of memory or more will show all of the eye candy drawn by Celestia v1.4.0 or later.

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 is compatible with them. In particular, Haze is not drawn.
(But the Mie and Rayleigh parameters of Celestia v1.5 can be used to generate haze using any graphics hardware that supports OpenGL v2.0)

b) Graphics cards with drivers that support OpenGL v2.0 will show all but Haze. Graphics cards that support only 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. Starting with Celestia v1.4.0, smooth shadow borders can be drawn by any card which supports OpenGL v2.0.

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. These problems seem to have been fixed in spring of '05. 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 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...
-- Most ATI cards, including the X series, cannot show surface texture images larger than 2K on a side on Rings, on 3D Mesh models, or on moving Clouds. Unfortunately, some Addons include 4K textures. Those Addons only work with Nvidia 4nnn, 5nnn, 6nnn and 7nnn cards and with ATI X1800 and above with ATI's most recent graphics drivers. Those 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 v1.4.0 uses OpenGL v2.0 for these features, so they can be seen on ATI 9500 cards or better.

As of February, 2004, only Nvidia and ATI have invested the effort in providing OpenGL v1.4 and v2.0 in summer of '05. 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.

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Q5:
Why are my favorite stars not in Celestia?

A5:
Celestia's primary star catalog is based on the Hipparcos database of stars with
accurately measured distances. They did not measure the distances to
dim or variable stars, including close doubles.

Grant Hutchison has contributed catalogs of stars closer than 25 LY and of stars known to have planets and Fridger Schrempp has contributed a catalog of double stars to Celestia v1.4.1.

Someone may have
created an Add-on that includes your stars, though. Or consider
creating the necessary STC file yourself and contributing it.
=================================================

Q6:
Where is the documentation?

A6:
An introductory User's Guide by Frank Gregorio is available in English.
Translations into German, French and a few other languages also are available.
Consider providing a translation into another language yourself.
Links to various versions of the documentation are on the Web.
Start with http://www.shatters.net/celestia/documentation.html
and
http://www.celestiamotherlode.net/catalog/documentation.html

Also see the Celestia WikiBook at
http://en.wikibooks.org/wiki/Celestia

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

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The questions below link to their answers.
Those answers may be further below or on other Forum pages.
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Q7: The Sun and the Moon are much too small in Celestia. What's wrong?

Q8: 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?

Q9: Celestia's galaxies are ugly, dim, grey blobs. How can I get colorful galaxies that look like the real things?

Q10: Sometimes a screenshot captured in Celestia will have multiple boxes around it, as if Multiview was on. How can I get rid of it?

Q11: I can't turn off the Red/Green diamond in the center of the selected planets.

Q12: Why are there no stars beyond about 16,000 light years? Why are there no stars in distant galaxies?

Q13: Why won't the "Set Simulation Time" menu let me put in a date before 1752 ?

Q14: Sometimes the planets and moons are way far away from where their orbits are drawn. Why?

Q15: I want to write some scripts for Celestia. How can I do it?

Q16: 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?

Q17: What changes have been made to Celestia since the last version?

Q18: When I try to capture a picture or movie, the image is stretched out of proportion.


Q19: How can I make Celestia work like a planetarium? I want to see how the sky should look from my backyard.

Q20: Why can't I see Mir? I know it's defined in Celestia.

Q20 Addendum

Q21: 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????

Q22: My planet's rings are drawn as a featureless oval. It used to work. What's wrong?

Q23: Celestia's orbit for the ISS is out of date. How can I get a better one?

Q24: 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?

Q25: 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.

Q26:Why don't Windows and Mac Addons work under Linux?

Q27: Satellites orbiting the Earth are drawn extremely bright with no shading. What causes this?

Q28: Stars with HIP, HD and SAO designations sometimes show up in the "tab completion" line and sometimes do not. What's going on?

Q29: Why does Celestia always use 100% of the CPU? How can I make it use less?

Q30. Celestia v1.5 is drawing planets and moons bright red. Why?

[selden]

Q7:
The Sun and the Moon are much too small in Celestia. What's wrong?

A7:
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

Here's a simple experiment suggested by "HarrieS", a guest on this 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?

[Dalle]

A7 cont.: 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.

[selden]

Q8:
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?

A8:
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.

[selden]

Q9:
Celestia's galaxies are ugly, dim, grey blobs. How can I get colorful galaxies that look like the real things?

A9:
The real things are dim, grey blobs. Your eyes are not sensitive to color at the very low light levels emitted by distant galaxies.

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.

Celestia v1.4.0 and later incorprates an improved rendering of galaxies. Galaxy brightness can be increased by typing a ")" (shift-0) or decreased by typing a "(" (shift-9).

[Guest]

Q10: Sometimes a screenshot captured in Celestia will have multiple boxes around it, as if Multiview was on. How can I get rid of it?

A10: This is a bug in Celestia similar to Selden's FAQ above. To make a good clean screenshot image, press [Ctrl + D] before you capture the image. This cancels Multiview.

[ElPelado]

Q11: I can't turn off the Red/Green diamond in the center of the selected planets.



A11: You have to press Ctrl+k.
Markers can be turned on and off in the "Render/View Options..." menu of Celestia v1.3.1 pre3 and later.



_______________________________________________________
ElPelado

[selden]

Q12:
A) Why are there no stars beyond about 16,000 light years?
B) Why are there no stars in distant galaxies?

A12:
A) Hipparcos could only measure parallax to a value of about 1 milli-arc-second.
For details, please read the thread http://www.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://www.shatters.net/forum/viewtopic.php?p=9424, Chris wrote about some of the tradeoffs in the current version of Celestia.

[selden]

Q13:
Why won't the "Set Simulation Time" menu let me put in a date before 1752 ?

A13:

This has been fixed in Celestia v1.4.0

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 previously used 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.

[selden]

Q14:
Sometimes the planets and moons are way far away from where their orbits are drawn. Why?

A14:
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

Code: Select all

OrbitPathSamplePoints  100

[selden]

Q15:
I want to write some scripts for Celestia. How can I do it?

A15 a
Celestia includes 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

An example .CEL script is Celestia's own start.cel, which is on your computer in Celestia's main directory.
Another example is the script at http://www.shatters.net/~t00fri/images/start-pandemo.cel

A .CEL Scripting Guide is available in English and German on the Documentation Page of the Celestia MotherLode.

http://www.lepp.cornell.edu/~seb/celestia/celestia_notes.html#4.0, includes a list of some of the more recently added .CEL scripting commands, but they're rather cryptically organized.

A15 b
Starting with Celestia v1.3.1, the Lua programming language is available for use in .CELX scripts. See http://www.lua.org/.

A few example Lua scripts for Celestia are available on SourceForge at http://celestia.cvs.sourceforge.net/celestia/celestia/scripts/

A .CELX Scripting Guide is available in English on the Documentation Page of the Celestia MotherLode.

More information about CELX is available on Harald Schmidt's web site at http://celestia.h-schmidt.net/


A15 c
You can use any language you want if it can pass commands to the operating system's command interpreter: it can run Celestia and tell it to run a .CEL Celestia script or .CELX Lua script.

When invoked from a command line, Celestia can be passed the name of a .CEL or .CELX script to run at startup:

Code: Select all

./celestia --url name-of-script.cel

When the command line includes the qualifier "--once", the command line will be passed to the running copy of Celestia instead of starting a new copy of the program. (note: two hyphens)

Code: Select all

./celestia --once --url name-of-script.celx

Note: as of Celestia v1.3.1, scripts may be in any folder. Previously they had to be in Celestia's "root" folder. It helps with your organization of your Celestia folders if you keep them in a folder named /scripts/.


For more information, please visit and contribute to the Celestia Scripting Forum

[reorganized 10sep06]

[granthutchison]

Q16: 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?

A16: 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.

[don]

Q17:
What changes have been made to Celestia since the last version?

A17:
The developers maintain a list of all new functionality and bug fixes in the Celestia ChangeLog, which is located at SourceForge: http://celestia.cvs.sourceforge.net/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.

[don]

Q18:
When I try to capture a picture or movie, the image is stretched out of proportion.

A18: (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.

[selden]

Q19:
How can I make Celestia work like a planetarium?
I want to see how the sky should look from my backyard.

A19:

If you're running Celestia v1.3.0 or later

0) Select the body from which to observe; the Earth maybe
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 Linux versions often don't.)