# Introductory Text

Celestia provides photo-realistic, real-time, three-dimensional viewing of the Solar System, the galaxy and the universe. It is an easy to use, freely-distributed, multi-platform, open source, software package which has become a valuable tool for astronomy education. Used in homes, schools, museums and planetariums around the world, it also is used as a visualization tool by space mission designers. Versions are available for computers running Windows, Macintosh (Mac OS X) and Linux operating systems.

Although it is optimized for 3D astronomical visualization, Celestia can be used to display and explore other 3D environments, too.

And, for some reason, many people seem to find exploring with Celestia to be a lot of fun.

## Using Celestia

How to use Celestia is described in detail in Frank Gregorio's Celestia 1.6.0 User's Guide.Template:Celestia/About this guide

## Why would anyone want to use Celestia?

• Because you have an interest in outer space and in the exploration of space.
• Because it is Fun! That is, if you like to explore the Universe.
• Because it is Educational. With Celestia, you can learn about the Universe.
• If you are a teacher, you already have access to Frank Gregorio's Lesson Plans. These are designed to educate while they entertain bored young minds.
• Because if you are an Artist, it gives you all the freedom necessary to develop your ideas...
• If you don't have a telescope, you can still view the planets up close, and in person. You can also view their moons, orbiting spacecraft and a whole lot more.
• Because it is absolutely free. No charges or fees of any kind ever.
• Trajectory analysis?
•  ?

## Why not use some other program?

• Freeware
• Hayden Planetarium's Digital Universe Atlas
• Jason Harris' KStars
• 4D2U's Mitaka
• Martin Schweiger's Orbiter
• NCSA's Partiview
• Stellarium (partial)
• Clear Sky Institute's XEphem
• Shareware
• FMJ Software's StarStrider
• Commercial
• Software Bisque's Seeker
•  ?

Although ALL of the above software titles are useful in their own right, none of these allow such thorough journeys to the planets, their moons, the stars, the asteroids, the galaxies and the planetary nebulae - ALL in one place. These visits are up-close and personal and in vivid detail with exceptional graphics and animations. You can also visit many, MANY spacecraft and see what they look(ed) like in space.

## What Can't Celestia Do?

• Telescope control
• 180 degree field of view
• Sound
• 3D stereoscopic or anaglyph viewing
•  ?

# Using Celestia

## Getting Celestia to Run

 A reader has identified this chapter as an undeveloped draft or outline. You can help to develop the work, or you can ask for assistance in the project room.

## Introduction

You can easily install Celestia on computers running Windows, MacOS or Linux. If you are experienced in compiling programs from source code, you can also install it on computers running other operating systems.

The current version of Celestia is available at the download page on the Celestia Web site. The links on that page actually point to files in Celestia's repository on SourceForge.

Older versions of Celestia are also available from SourceForge.

Prereleases of the next version of Celestia used to be announced on the Celestia Web Forum in its Users Forum, but the forum no longer exists. If you build Celestia from source code, you can generate a pre-release of Celestia v1.7 which is quite stable.

## Windows

If you have downloaded the Windows version of the Celestia installation executable, then you simply need to run the .EXE file that you downloaded. It will install Celestia wherever you specify.

Although it was originally written for Windows XP, Celestia works fine when installed in any later version of Windows, from Vista through Windows 10.

A few words of caution to Windows Vista users, however... (These may also apply to Windows 7.)

If you run the setup program as a Windows XP-compatible application, you'll find that the program runs fine and that Celestia operates as it should. You can also run the Celestia executable in the native Windows Vista mode too.

Savvy Windows XP users will find that there are a lot of things to get used to in the XP-compatible mode though. If you modify a planet texture, for example, you may find that your modified texture was NOT saved to the Celestia program directory where you got it from originally.

Vista likes to create shortcuts to modified textures, and these - for some reason - aren't readily available to the Celestia program. If you're using Windows Explorer to view the Celestia texture files, click on the "Compatibility Files" area at the top of your screen to see your modified texture. If you like, you can then copy and/or move the new texture to the C:\Program Files\Celestia\textures directory of your choice.

Recommendations:

Vista users should install Celestia as a native Vista program. When Celestia is installed as a previous version of Windows-compatible program, it simply causes more problems than it solves.

Vista and later versions of Windows, including Win7 through Win10, are particularly protective of software installed in the Program Files directory tree. You will have far fewer problems if you install Celestia somewhere else. You could, for example, create the directory C:\MyPrograms\ and install Celestia there. The installation program lets you browse to wherever you want to install it.

## MacOS

Celestia is provided for Mac OS in a disk image. Once you have downloaded the file, simply open it and then copy the application file "Celestia" from the window that shows up to the "Applications" folder, as for most applications in the Mac OS.

## Linux

Every Linux distro does things a bit differently but the major ones do have some version of Celestia in their software repos.
For example:

fedora -- "yum install celestia"
-- but this is WITHOUT spice support

OpenSUSE -- "zypper in celestia"
-- also WITHOUT spice support

Debian -- "apt-get install celestia"

To be sure you have the most recent version of Celestia, you should consider building your own copy from source. Then consider contributing your results to the appropriate repo. Many repos have OLD versions in them since nobody has contributed an updated version. Some of the repos even have Celestia v1.5 in them. Celestia v1.6.1 was the last officially released version. If you build from source, you can generate a pre-release of v1.7, which is quite stable.

Few repos, if any, provide Celestia with SPICE support, so NO spice kernels will work if you install Celestia from an rpm or deb or xz.
Also there ARE NO prebuilt packages using qt 4 for KDE4, so no kde4 /qt 4 prebuilt rpm's, or deb's or xz's.

In the case of Ubuntu and other Debian derivatives, Celestia is split into free and non-free versions because of their strict interpretation of how licensing should be handled. Both are needed for Celestia to work properly.

## Building from sourcecode

 The text in its current form is incomplete.

## Introduction

Celestia uses OpenGL graphics routines to draw its pictures of the universe. Unlike DirectX, which is available only on computers running Windows, OpenGL graphics libraries are available for many different types of operating systems. OpenGL was originally developed by SGI but now is available for use on almost all computers and graphics hardware. The OpenGL WikiBook has more details.

Celestia can run on most computers, but to see all of its "eye candy" a modern graphics card implementing OpenGL v2.0 is essential. Even when the best available graphic cards have been installed, some computers have problems running Celestia because their graphics drivers are out of date or buggy. Regularly check the Web site of the manufacturer of your computer or of your graphics card to make sure you have the current driver version. Updated drivers are provided often.

## Graphics Card Limitations

Many graphics card limitations are described in Celestia's list of Frequently Asked Questions:

What graphics card should I get?

## Operating System Limitations

Many computer and O/S limitations are described in Celestia's list of Frequently Asked Questions.

### Linux

• OpenGL is distributed in many Linux flavors since is open source, but the graphic drivers not always are open source, thus, aren't included in all Linux distros.

### Mac OS X

• Graphics driver updates for Mac OS X are available in updates to Mac OS X itself, not in general as separate driver updates by NVIDIA or ATI. This means "upgrade your driver" on OS X means "make sure your version of OS X is up-to-date". You may have to spend money in order to get the current version of OS X.
• Point sprite primitives do not work on versions of OS X earlier than 10.4.
• Point sprites are not supported properly on Tiger (PPC and Intel architectures). Colors may appear incorrect, and hard freezes requiring a reset have been seen. VBO seems to be involved. Apple has been made aware that this is almost certainly a driver bug, but no fixes have been promised. Behavior on Leopard is unknown.
• The OpenGL 2.0 render path is only supported on Tiger 10.4.3 or later, regardless of the graphics card.
• Holes may appear in orbit paths on certain ATI configs. A workaround is being investigated. Fixed in 1.5.0.

### Windows

• The graphics drivers provided with your brand new computer hardware already are obsolete. Usually several months have passed between the time its software was configured and it was provided to you. Be sure to download and install the most recent graphics drivers provided on the Web site of the manufacturer of your computer's graphics hardware.
• Windows XP includes a software-only OpenGL library. It's used on systems without 3D hardware or when hardware acceleration is disabled in the Display Control Panel. It implements only OpenGL v1.1, Celestia's Basic rendering path, so it has limited functionality and runs rather slowly, but it is relatively bug-free.
• Celestia does not use DirectX, which is Microsoft's proprietary 3D graphics programming library. Unfortunately, whenever Microsoft's DirectX libraries are updated, the manufacturer's OpenGL drivers are replaced by obsolete versions provided by Microsoft. Whenever you update DirectX, be sure to reinstall the graphics drivers using the most recent versions provided by the manufacturer of your computer's graphics hardware.
 A reader has identified this chapter as an undeveloped draft or outline. You can help to develop the work, or you can ask for assistance in the project room.

## Introduction

When Celestia starts, by default it shows a 3D image in a window on the computer's main screen. Depending on its user interface, Celestia may be able to occupy the entire screen.

Image quality can be improved somewhat, too.

### Size

#### Linux

Celestia starts in a window, you can exter/exit fullscreen mode by typing Alt-Enter.

#### Mac OS X

Celestia starts in a window whose position and size are saved. Enter/exit fullscreen mode by typing Cmd(Apple)+F. Move your mouse to the top of the screen when in fullscreen mode to access the menu bar.

Right-clicking (control-clicking) on objects to bring up a context menu, switching to other applications, hide, and opening panels like Preferences and Help continue to work 100% in full screen mode. Multiple screens should be detected properly, although when switching to fullscreen mode Celestia currently only targets the screen which is most covered by the Celestia window.

Various display options can be accessed from Celestia > Preferences or the Display menu.

#### Windows XP, Vista and 7

Celestia starts in a window which is located in the same place and at the same size as when Celestia previously exited. The menu "Render / Select display mode..." provides access to the list of full-screen resolutions claimed to be supported by the graphics display.

### Edges

By default, Celestia does not enable anti-aliasing. This means that you'll see stair-step jaggies and moving dots on the edges of objects, especially on diagonal lines. Turning on anti-aliasing will make the display run more slowly, but objects will look better.

Celestia includes two different anti-aliasing options: a menu and keyboard option to smooth the orbital path lines, and a configuration file option to enable full-screen anti-aliasing.

You can separately enable various levels of full-screen antialiasing in the controls for your graphics hardware. This will affect all 3D programs, not just Celestia.

#### Menu and keyboard (orbit smoothing)

The Windows menu option Render/Antialiasing turns on hardware smoothing of the orbital path lines.

(What are the corresponding Linux, and MacOS menu options?)

The keyboard command Ctrl-X is available in all versions of Celestia to toggle this display rendering option.

#### celestia.cfg (full screen)

To enable full-screen antialiasing within Celestia, edit the file celestia.cfg. Find the line which currently says

# AntialiasingSamples 4

and delete the #. If your graphics hardware supports higher levels of antialiasing, you can increase its value appropriately. This feature will work only if your graphics hardware has been configured to allow application control of antialiasing.

#### hardware control panel (full screen)

Alternatively, you can open the software control panel for your graphics hardware and turn on its antialiasing features permanently. This will affect all 3D programs, not just Celestia.

In either case, while the edges of objects will look much better, Celestia will run more slowly. The framerate reduction will depend on the quality of your graphics hardware.

 The text in its current form is incomplete.

## Introduction

A Render path is Celestia's way of classifying graphics capabilities. Its different Render paths correspond to different sets of OpenGL functions.

Not all render paths may be available on your computer. A render path will be available only if your computer's graphics software includes the OpenGL functions that it uses. More sophisticated render paths require more recent graphics hardware, but not the most expensive version of a card.

When it is first started, Celestia automatically selects the best render path based on the graphics capabilities advertised by the computer's OpenGL library. However, you can interactively select any available render path. Celestia remembers which path you selected last and will use it when the program is restarted. Choosing another render path may be necessary if there are problems due to bugs in your computer's graphics drivers.

To select an alternate render path, type a Ctrl-V. That is, press the "V" key while holding down the "control" key. This causes Celestia to switch to the next available render path. The name of the newly selected render path will be shown briefly in the lower left hand part of Celestia's window.

## Render Paths under Linux

see the windows it is THE SAME

## Render Paths under Windows

Some of the render paths available on computers running Windows are

• Basic
• Multitexture
• OpenGL Vertex Program
• OpenGL Vertex Program/Nvidia combiners (only on Nvidia graphics cards)
• OpenGL 2.0

Celestia can show more and improved "eye candy" when using the later render paths:

• Basic requires OpenGL v1.1.
It shows the fewest effects. It's available even on systems which have only Microsoft's software support for OpenGL and have no 3D hardware acceleration.
• Multitexture requires OpenGL v1.2.
It adds NightLights and the shadow of a planet on its rings.
• OpenGL Vertex Program requires OpenGL v1.4.
It adds specular highlights on oceans, shaded mountainsides and the shadows of rings on a planet.
• Nvidia Combiners adds a rudimentary haze effect. (Only for Nvidia graphic cards)
• OpenGL 2.0 requires OpenGL v2.0.
It improves the edges of eclipse and ring shadows, draws the shadows cast by as many as four separate light sources, and adds sophisticated atmospheric effects, including cloud shadows on the ground. Haze can be drawn, too, based on Mie and Rayleigh scattering functions. (These scattering functions are available only with Celestia v1.5.0 or later.)

## OpenGL Versions

To find out what version of OpenGL the graphics drivers on your computer claim to support, select Celestia's Help menu. The entry "OpenGL Info..." will list details about your computer's graphics hardware and software.

 The text in its current form is incomplete.

## Introduction

Celestia can be started either by clicking on its icon or by typing a command into a terminal window. Under Windows, the terminal window is often called a DOS window or CMD window.

A typical command to run Celestia might be

cd Celestia
./Celestia


The command line can optionally include the following qualifiers. These qualifiers are different depending on which command interface Celestia was built for. Each command qualifier (aka switch) should be prefixed by two hyphens

## Windows command qualifiers

• --dir <path>
Change root celestia directory to <path>
• --fullscreen
Start Celestia in fullscreen mode
• --once
Send the command line to a running instance of Celestia. If no running instance exists, a new one is started.
• --url <url>|<filename>
Start in the given <url> or if the parameter is the name of a script file, execute <filename>.
• --verbose >    <filename>
Write debug messages to <filename> (Although --verbose can only write to a file, the redirection > is required.)

## gtk command qualifiers

• --conf
Use alternate configuration file
• --dir
Use alternate installation directory
• --extrasdir
Use additional "extras" directory
• --fullscreen
Start full-screen
• --nosplash
Disable splash screen
• - v [0|1]
Enable debug mode.

## KDE command qualifiers

• --conf
Use alternate configuration file
• --dir
Use alternate installation directory
• --extrasdir
Use additional "extras" directory
• --fullscreen
Start full-screen
• --nosplash
Disable splash screen
• +[url]
Start and goto URL
• <url>
Start in the given url/execute script file.
• - - help
Command-line help

## Exploring Celestia's Universe

 The text in its current form is incomplete.

## Introduction to using Celestia

To start Celestia, you should double-click on its icon. As it starts, it first shows the Sun, and then takes your viewpoint to the sunlit side of the Earth. When you get there, you can tell Celestia to show you other interesting sights.

Initially, Celestia opens in a window on your screen. For a more immersive experience, you can tell Celestia to take over the entire display. Open Celestia's menu Render/Select Display Mode and choose an appropriate screen resolution. When it's in full-screen mode, if you move the cursor up to the top of the screen, you should see Celestia's menu bar again, where you can choose to go back to windowed mode.

Some may think Celestia is a game. In a way it is but it is much more than that. Like most programs (with graphics and objects) of today the mouse is the primary way of getting around. Celestia does use the mouse to rotate/panned the observers POV with a combination of left and right mouse click and drag functions. However to truly get the most out of Celestia the keyboard shortcut letters bring the full power and beauty of the program into play. People who are more game enthusiasts may find the interface of Celestia boring after a few minutes if they only use the mouse. So, start learning and memorizing the keyboard shortcuts. You can find a quick look of the keyboard shortcut commands in the Help/Control pulldown while the program is running. You can also find them in the Celestia User's Guide.

Below are some introductory events and places you can explore in Celestia, using the keyboard and mouse. You will notice below some letters and words are in bold face. These are the keyboard shortcuts that can be typed to control Celestia.

## Earth's rotation and the pole star

This needs a fairly wide field of view – use the comma (,) and dot (.) keys to adjust the window to around 60°. If you don't have the Earth on the screen, press the three keys H3G to go there. Then back away a little with the End key or your mouse's wheel. Adjust the number of stars with the [ and ] keys, setting a limiting magnitude of around 5.

Adjust the rate of time to 1000 times faster (LLL) so the Earth can be seen slowly turning. The Earth spinning is what gives us day and night. Type a "y" to hover over one point on the Earth and see it enter light and shadow (day and night) as the Earth turns. Use the arrow keys Shift-← and Shift-→ to move round the Earth and see where night and day start and end. You can put the mouse cursor over a piece of land and just watch that point as day and night pass over it. This is best done with the clouds turned off (I). To turn the "sync orbit" off again, you can press F to return to "follow" mode.

With the synchronous orbit on, back away from the Earth a little using the End key (or the rotary wheel of your mouse if it has one) so you can see more stars. You can press the Home key to move closer again. As you watch the stars go past, you might see distinctive patterns of stars go by. People used to imagine people and animals in the patterns in the stars. Press / to turn on the constellation lines, and = to turn on their names. You can use the space-bar to pause time and take a longer look at any interesting shapes.

With the mouse, right-click and drag upwards to turn to look more Northwards. By the time you are looking squarely at the South pole of the Earth, the pole star Polaris should be visible. It's the star that's at the end of the tail of Ursa Minor, the "Small Bear", often called "the Little Dipper". If you watch for a while, you will see that all stars seem to revolve around that point while Polaris itself doesn't move much at all.

Keeping this view, zoom closer to the Earth (Home) and notice the way day and night look on Earth from this view. Depending on the time of year, the Antarctic ice-cap might be on permanent daylight or permanent shadow. This can be easier to see if you speed up to 10000x (L). You can briefly speed up even more (use K to slow down again) to hop between seasons.

## Other Planets

Start Celestia. You are looking at the Earth from the direction of the Sun. We want to look at the Earth from the other side. Back away from the Earth using the End key until the Earth is about the size of a pea, and then use Shift-← and Shift-→ to rotate around the Earth until the Sun is visible in the background. The Earth might be easier to see if you turn up the background illumination with the } key, although this is not realistic as it makes planets glow in the dark (only stars really do that). Now turn the time rate up to a million times faster by typing LLLLLL.

You should notice the Moon whizzing round the Earth. Move closer or further away (Home/End) until the moon uses the whole width of the screen. The Moon takes about 28 days to go round the Earth. If you slow down time a bit by pressing K, you should be able to count the number of days (turns of the Earth) it takes for the Moon to go round once. You can turn the Moon's name on and off by pressing M. If you see a giant mass of names appear, all together, it's probably the names of all Jupiter's moons in the distance – Jupiter has a lot of moons. Speed back up to a million times again.

You will notice that every year as the Sun goes past, it is accompanied by a collection of small bright dots. These are other planets. You can turn their names on and off with P. It's time to leave the Earth. Type HFC to follow and centre the Sun. Leave planet names on (P). Back away from the Sun a little and you will be able to see Mercury, Venus, Earth and Mars moving from side to side as they orbit the Sun. If you back away further you will be able to see 9 planets. The outer ones don't seem to be moving much, so press L speed things up a little. Time is passing at about a year every 4 seconds now.

Let's turn on the planet's orbit lines – press O. They're not very clear seen edge on, so use the right mouse button to drag downwards until the orbits look circular, seen from above. You can't see all the orbit lines at once – if you move far enough away to get Pluto's orbit in, then the inner planet's orbits disappear. Move in to see the inner planet's orbits and the outer orbits are off the screen. By right-dragging, you can get a good edge-on view that shows that all the orbits are in almost exactly the same plane except for Pluto.

You may notice as Jupiter goes past that it has a huge mass of orbit lines for its many moons. Four of them are big enough to be seen from the Earth by using binoculars.

Time for a quick tour. This is possible best done with the orbit lines switched on. First, to about 1000x time rate (K,L). Then we can visit the 9 planets by typing 1G, 2G etc. Each of the number keys corresponds to a planet. Use Home and End (or the mouse scroll wheel) to zoom in and out, and right-drag to change the viewpoint and get a good look at each planet.

While visiting the outer planets, it is worth looking from above to see just how much like a little solar-system their moons make. You may occasionally see a black spot move across the sunlit surface of Jupiter – this is the shadow of one of the moons as it passes between Jupiter and the Sun.

## Other Stars

Not all stars are like the Sun. Some stars are hotter than the sun, some cooler, bigger, smaller, brighter and dimmer, redder, bluer. Actually the blue ones are hotter, and the red ones cooler.

You cannot tell how far away stars are by just looking at them. So when people invented the constellations, they drew lines using stars that might be nearby, or far away. A good demonstration of this is to see how distorted familiar constellations would look if seen from a different angle – from a different place.

Turn on the constellation lines (/) and use dot and comma to set the field of view to around 60°. Centre a star in the constellation of the plough (Ursa Major, also called the Big Dipper) by pressing the Enter ()key, typing the name megrez and enter again. Then type CF to centre and follow the star. Now hold down the right mouse key and drag around the screen. Your viewpoint is now many light years away from the Earth, orbiting around the distant star Megrez. Try both with and without the constellation lines. You can plainly see the 3D pattern of the stars. If you move right round the back of the Plough (or Big Dipper), you can see that all the constellation lines seem to point roughly in the same direction – the direction of Earth.

It is interesting to return to the Sun while maintaining your view on Megrez – press T to track Megrez (keep it centred), then HG to go home. You can see the constellations return to their familiar shapes as we get back to the Sun. Press T again (or Esc) to stop tracking Megrez.

Another good star to do this with is Arcturus in the constellation of Boötes.

The constellations are all drawn with stars that are visible from the Earth, and are therefore the nearest stars to us. Turn the constellation lines on and then back a long way away (hold End), until all the lines are visible on the screen. Turn on more stars by holding the ] key and raise the limiting magnitude to about 10. Back away a little more until the whole of the galaxy is visible on the screen. Then right-drag so the galaxy is seen edge-on. You can see that the stars in the Celestia program form a sphere round the Sun. This is because we don't know the distances of all the other stars in the galaxy well enough to put their positions in the program – so the rest of the galaxy is just shown as a 'mist' of stars.

Reduce the limiting magnitude to 10 or less again with the [ key.

## Other Galaxies

You can fly to another galaxy much like our own by pressing ↵m 31↵g. You can always go home again by typing the keys H3G.

 A reader has identified this chapter as an undeveloped draft or outline. You can help to develop the work, or you can ask for assistance in the project room.

## Introduction

Celestia includes several catalogs of Locations on the Earth and on objects elsewhere in the Solar System. They're short, only containing lists of major features, like the Earth's oceans, continents and capital cities of nations. More extensive catalogs of Locations are available as Addons.

Locations are labeled positions, usually on the surfaces of objects defined in SSC catalog files. They're shown if you select the option "Label Features" in the menu Render / Locations...

When Locations are enabled, you can use Celestia's goto functions to travel to them.

• =Mouse and Keyboard Controls Used for Navigation in Celestia=

## Mouse Functions:

Celestia works best with a three-button wheel-mouse. Very inexpensive ones are available which work well with Linux, Mac and Windows computers.

Left drag: Orient the view.

Right drag: Orbit the selected object.

Wheel: Adjust the distance to your current selection.

Right + Left drag: Adjust your distance to the selection.

Ctrl + Left drag: Adjust your distance to the selection.

Shift + Left drag: Changes your field of view (e.g. => Telescopic view.)

Wheel click: Toggles the field of view between 45 degrees and the previous field of view.

Left - click: Select the object you click on.

Left double click: Center the selection.

Right - click: Brings up the context menu.

## Keyboard Navigation Commands:

H  : Select the sun. (Home.)

C  : Center on the currently selected object.

G  : Go to the currently selected object.

F  : Follow the selected object.

Y  : Orbit the selected object at a rate synchronized to its rotation.

:  : Lock on the selected object.

"  : Chase the selected object. (The orientation is based on the selected object's velocity.)

T  : Track the currently selected object. (Keep the selected object centered in the view.)

HOME : Move closer to the currently selected object.

*  : Look back. Causes the view to shift from objects forward in the direction of motion, to objects rearward.

END  : Move farther from the selected object.

ESC  : Cancel the currently executing motion or script.

Shift+C  : Center/orbit. (Center the selected object without changing the position of the reference object.)

Left : Move (or roll) the camera view left.

Right: Move (or roll) the camera view right.

Up  : Move (or pitch) the camera view up.

Down : Move (or pitch) the camera view down.

Shift+ Arrow: Orbit the currently selected object in the direction indicated by the arrow selected.

1-9  : Select any of the planets orbiting our Sun. (2=Venus, 4=Mars, etc.)

ENTER  : Select a star or planet by typing its name.

Ctrl+C, or Ctrl+INS  : Copy location URL to your clipboard.

## Time Control:

Spacebar : Pause/Resume the flow of time and scripts (toggle)

J : Reverse/Forward time (toggle)

\ : Set time rate: 1x forward (norm), cancels faster/slower x factors

L : Change time rate : 10x faster

K : Change time rate : 10x slower

Shift+L : Change time rate: 2x faster

Shift+K : Change time rate: 2x slower

! : Set time to current system date and time

? : Display light-travel delay between ovserver / selected object

- (hyphen) : Subtract light-travel delay from current simulation time

## Labels (on/off Toggles):

E : Galaxies

Shift+E : Globulars

B : Stars

P : Planets

Shift+P : Dwarf Planets

M : Moons

Shift+M : Minor Moons

W : Asteroids

N : Spacecraft

= : Constellations

& : Locations

## Render/Display (on/off Toggles):

U : Galaxies

Shift+U : Globulars

^ : Nebulae

Ctrl+A : Atmospheres

I : Clouds

Ctrl+L : Night side maps

Ctrl+T : Comet Tails

Ctrl+E : Eclipse Shadows

Ctrl+B : Constellations bounaries

/ : Constellation diagrams

; : Earth-based equatorial coordinate sphere

Ctrl+K : Markers (placed on objects)

O : Orbits (toggle ALL selected orbits)

## Render Options:

{ : Decrease Ambient Light

} : Increase Ambient Light

( : Decrease Galaxy Light Gain

) : Increase Galaxy Light Gain

[ : Decrease Magnitude Limit :

          -  If AutoMag OFF : Decrease limiting magnitude (fewer stars)
-  If AutoMag ON  : Decrease limiting magnitude at 45 deg FOV


] : Increase Magnitude Limit :

          -  If AutoMag OFF : Increase limiting magnitude (fewer stars)
-  If AutoMag ON  : Increase limiting magnitude at 45 deg FOV


Ctrl+Y : Toggle Auto Magnitude (auto adaptation of start visibility of FOV)

, : Narrow Field of View [Shift+Left Drag]

. : Widen Field of View [Shift+Left Drag]

Ctrl+X : Toggle Antialias lines

Alt+Enter : Toggle Display mode (Full-Screen / Windowed)

Ctrl+P : Mark selected object

+ : Toggle Planet Texture type (Artisitic / Limit of Knowledge)

% : Star color table toggle

Ctrl+S : Cycle the Star Style (points / fuzzy discs / scaled discs)

V : Cycle the Info text verbosity (None / Terse / Verbose)

Ctrl+W : Toggle Wireframe mode

## Spaceflight:

F1 : Stop.

F2 : Set velocity to 1 km/s.

F3 : Set velocity to 1,000 km/s.

F4 : Set velocity to speed of light.

F5 : Set velocity to 10x the speed of light.

F6 : Set velocity to 1 AU/s.

F7 : Set velocity to 1 ly/s.

A  : Increase velocity.

Z  : Decrease velocity.

Q  : Reverse direction.

X  : Set movement direction toward center of screen.

4  : Yaw left.

6  : Yaw right.

8  : Pitch down.

2  : Pitch up.

7  : Roll left.

9  : Roll right.

5  : Stop rotation.

## Joystick Controls:

X axis  : Yaw.

Y axis  : Pitch.

L trigger : Roll left.

R trigger : Roll right.

Button 1  : Slower.

Button 2  : Faster.

 The text in its current form is incomplete.

## Introduction

Celestia provides you with very powerful and flexible ways to control your view into Celestia's simulation of the cosmos. Once you understand how to manipulate its interactive controls, you can quickly and easily position yourself to view the astronomical phenomena that interest you. If is helpful to think of Celestia as providing a remotely-controlled camera that is at your command. The view that you see on your screen is determined by the location of the camera, the direction the camera is pointing, and the magnification of the camera's zoom lens. Each of these factors can be controlled independently.

One important thing to understand is that both the location and direction of the camera are specified relative to some frame of reference. The frame of reference may be attached to a moving object (such as a planet or moon). If so, then the actual location and direction of the camera (with respect to absolute space) will automatically change as the object moves. This is often very convenient, because it means that you do not have to continuously change the camera location and direction manually in order to keep the object in view.

Commands which change Celestia's view of the universe are described in the file Celestia/controls.txt

## Zoom Control

The magnification of the camera's zoom lens determines how large or small objects will appear on your screen, and also how much of the environment around you is visible (the field of view). If you increase the magnification then objects will appear larger, but you'll have a smaller area in view. (You can also make objects appear larger by moving the camera closer to them. The difference between zooming and moving the camera is important, as we will explain below.) Celestia displays the current magnification factor and field of view in the lower right hand corner of the window. As you zoom in, the magnification factor will increase, and the field of view will decrease. Zooming out has the opposite effect. If you zoom out to a very large field of view, the view will become distorted, much like what you would see with a fish-eye lens.

Repeatedly typing a comma (,) narrows the field of view, increasing the magnification. Repeatedly typing a period (.) widens the field of view, decreasing the magnification.

 The text in its current form is incomplete.

There are several keys that can be used to control the rate and direction of the passage of time.

## Table of keys

### Effect

J Reverse time
K Decrease rate by 10x
Shift+K Decrease rate by 2x (new in version 1.5.0)
L Increase rate by 10x
Shift+L Increase rate by 2x (new in version 1.5.0)
Space Stop time
! Set time to the computer's current time
? Display travel time for light between observer and selected object
- Subtract the above light travel time from Celestia's current time
\ Set time to real time
 The text in its current form is incomplete.

## Introduction

A Cel: URL is a bookmark that saves the time, location, rendering options and other settings of a specific Celestia event or place. These URLs can be exported and published as regular HTML, so that any Celestia user can share a Celestia scene with any other.

The Windows version of Celestia includes a Bookmark menu. Those bookmarks are not the same as Cel: URLs.

To record a Cel: URL to your computer's "clipboard", type a Ctrl-C, or the usual "copy selected region" keyboard shortcut. On a Windows system, you can type a Ctrl-Insert.

To paste a Cel: URL into a document, type a Ctrl-V, or the usual "paste clipboard".

## Potential incompatibility warning

Unfortunately URLs recorded by one version of Celestia often are not compatible with other versions. The origin of Celestia's coordinate system changed in V1.5. As a result, URLs recorded by previous versions of Celestia place the viewpoint hundreds of AU from the intended viewpoint. Similarly, the rotation of the Earth was greatly improved in Celestia v1.6. As a result, URLs recorded by V1.5 for viewpoints on the Earth's surface will place the viewpoint tens of kilometers from the intended viewpoint. Also, although URLs recorded by previous versions of Celestia can be read by V1.6, the URLs generated by V1.6 cannot be used by previous versions of Celestia.

## Fix for Linux if clicking on a Cel: URL does not work

Depending on the specifics of your installation, Celestia might not have been registered to handle the Cel: URLs. If that is the case, you can remedy as follows (this should work on any system compliant with the XDG specifications).

1. Enter xdg-mime default celestia.desktop x-scheme-handler/cel in a terminal. (This registers Celestia as the program that handles cel: links.)
2. Edit celestia.desktop, replacing the line Exec=celestia-gnome with Exec=celestia-gnome %u, so that the system knows that it has to pass the URL argument to Celestia, when launching it. The desktop file is usually found in /usr/share/applications/ and if you don't want to edit files with root, you can instead copy it to $HOME/.local/share/applications/ and edit it there (or more generally copy it from $XDG_DATA_DIRS/applications to \$XDG_DATA_HOME/applications/). Optionally, you can also add MimeType=x-scheme-handler/cel; to the desktop file. (See the XDG desktop entry spec.)
 A reader has identified this chapter as an undeveloped draft or outline. You can help to develop the work, or you can ask for assistance in the project room.

## Introduction

Under some operating systems, Celestia can create a snapshot, recording its current on-screen display to a file. It also may be able to create a video recording of a sequence of frames while it is running. Other operating systems may require an external screengrab or video recording program.

## Linux

Currently video recording from within celestia does not work. A file is created, however it is empty.

Image screenshots work as expected.

## MacOS X

Screenshots and movie recording have not yet been implemented in the osX version of Celestia. For the moment you can use system commands to take some screenshots.

Some people have reported that CaptureMe does a reasonable job of recording movies.

## Windows

When running the Windows version of Celestia, both snapshots and movies can be created:

• Select the menu option "File/Capture Image..." or type the <F10> key to record a snapshot of the current view.
• Select the menu option "File/Capture Movie..." or type <Shift-F10> to start recording a movie of what Celestia is showing.
• Type <F11> to actually start (or pause) the recording.
• Type <F12> to finish recording.

## What is Celestia?

Celestia is a freely-distributed, multi-platform, open source software package that provides photo-realistic, real-time, three-dimensional viewing of the solar system, the galaxy and the universe. It has proved a valuable tool for astronomy education, and is used in homes, schools, museums and planetariums around the world. Versions are available for Windows, Macintosh (MacOS X) and Linux computers.

The Celestia Website has some additional information about Celestia.

The Celestia Forum is a good place to look for or ask for additional information. You'll find lots of friendly people there.

The Celestia Motherlode has many Celestia resources.

### Where can I get the most recent version of Celestia?

Prerelease versions are announced in the Celestia Web Forum in its Users Forum.

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

The developers maintain a list of all new functionality and bug fixes in the Celestia ChangeLog, which is located at SourceForge (most recent changes listed at bottom).

## Questions about how Celestia works

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

Celestia makes use of the most advanced features of OpenGL that your computer's graphics driver claims to support. Many older OpenGL implementations have serious bugs. Here are some options for improving Celestia's display, with the most likely ones first:

1. Make sure full hardware acceleration is enabled in your display properties.
2. Upgrade to the most recent drivers for your graphics card. Download them for free from the Web site of the manufacturer of your card, not from Microsoft.

Nvidia drivers can be downloaded from http://www.nvidia.com/content/drivers/drivers.asp

ATI drivers can be downloaded from http://ati.amd.com/support/driver.html

Notes:

1. Graphics chipsets integrated into laptop systems usually require drivers provided by the manufacturer of the laptop itself. Too often proprietary "glue chips" prevent the chip vendor's drivers from working properly.
2. Reduce or disable hardware acceleration to verify that the problem is hardware related.

#### Windows XP

1. Whenever you upgrade Microsoft's DirectX software, you must upgrade or reinstall the graphics hardware manufacturer's graphics drivers afterward. Installing DirectX installs Microsoft's copies of the drivers, which usually are several generations old.
2. To disable hardware acceleration 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, but seems to have relatively few bugs. It does everything in software, works on 2D displays, and is quite slow.
3. Driver Upgrade Procedure
2. use the Control Panel / Add or Remove Programs menu to delete the current graphics drivers.
3. Reboot
4. Cancel out of XP's offer to install new drivers.
5. Run the Installation program for the new drivers.
6. Reboot
7. 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.

#### MacOS X

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.

#### Linux

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.

### Celestia draws the Moon in shades of purple, blue and red. Why is it doing that and what can I do?

Your graphics chipset and its drivers aren't drawing bumpmaps and normalmaps properly: their OpenGL routine "GL_ARB_vertex_program" is defective. (This is often seen with the newer Intel graphics chips.) Assuming you've already installed the most recent drivers,

1. Download and install a different version of Celestia. The program is frequently revised.
2. Turn off some of Celestia's advanced display features.
1. Type a [Ctrl-V] several times to select "Basic" or "Multitexture" render paths instead of the OpenGL Vertex programs. This disables the use of vertex and shading programs temporarily. If this does improve things after you've followed the previous suggestions, then you need to do the next step:
2. 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
IgnoreGLExtensions [ "GL_ARB_vertex_program" ]

Celestia's Help menu lists all of the routines in your system's OpenGL library. Add equivalent Ignore lines for other suspicious routines.

Addendum provided Tech Sgt. Chen:

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.

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

Report the exact circumstances and details of your hardware and software in the "Celestia Bugs" forum. Celestia runs on many different hardware and software configurations. It is not appropriate to ask people to guess what you have. 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 3.2, OpenGL v1.3.9088
Program: Celestia v1.3.0


Hopefully you know the System information. If you're running Windows, System details usually are available in the Control Panel's System Properties menu.

Some of the Graphics information can be found in Celestia's Help menu. If you're running Windows, more details can be found in the Control Panel's Display Properties menu.

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

Older versions of Celestia are available on SourceForge v1.2.4 is extremely robust, but does not include many recent features.

"Prerelease" versions of Celestia for Windows often are available on Shatters.net. Look in http://www.shatters.net/celestia/files/ and http://www.shatters.net/~claurel/celestia/files/ The most recent "prerelease" (e.g. V1.5.0pre3 or later) may work for you, but may be even worse.

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

Cards based on Nvidia FX 5nnn, GF 6nnn, 7nnn, 8nnn or newer chipsets with 128MB of memory or more will show all of Celestia's eye candy. For example, an inexpensive FX 5200 will show all of the eye candy drawn by Celestia v1.3.2 and v1.4.0, althogh not as quickly as more expensive cards.

All other cards have limitations or problems when used with the current versions of Celestia.

1. Any graphics card with drivers that support OpenGL v1.4 will show most, but not all, of the eye candy. (e.g. Nvidia GF4 Ti 4nnn series cards cannot show smooth shadow borders although it can show haze; No ATI Radeon cards can show haze or smooth shadow borders. The ATI limitations may be solved in Celestia v1.4.0 when it is finished.)
2. Other cards work, too, but with various additional limitations. (e.g. Nvidia MX cards cannot show ring shadows cast on planets; ATI Rage cards cannot show specular highlights or bumpmap shadows.)
3. Many graphics chipset designs, as well as Microsoft's OpenGL software, are limited to displaying Celestia's Basic and Multitexture "Render Paths". They can't display bumpmaps or specular reflections, for example.

Background:

Starting with Celestia v1.4.0, you will be able to see multiple shadows cast by multiple light sources if your card supports "GL_ARB_shading_language_100" and "GL_ARB_fragment_shader". These routines are part of the OpenGL V2.0 standard, but are included in the v66.nn and later ForceWare graphics drivers for Nvidia FX 5nnn and later cards. They also are included in the v4.nn and later Catalyst graphics drivers for ATI's Radeon 9500 cards and higher.

Starting with Celestia v1.3.2, improved eclipse and ring shadows are visible if your card has "GL_ARB_fragment_program" and uses floating point to do the graphics calculations. Unfortunately, Celestia v1.3.2 supports these features only on Nvidia FX 5nnn and GF 6nnn cards and not on any others.

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".

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

### 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?

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

This bug seems to be fixed in Celestia v1.4.0 and later, which is available on SourceForge.

Here are some suggestions for minimizing this problem:

1. Often the problem will go away if you toggle "Show Galaxies" off and on again before you take your snapshot. Either you can use the Render/View Options menu or you can type the letter "U" twice before you press "F10".
2. 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".
3. 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.
4. 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.

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

To make a good clean screenshot image, press [Ctrl + D] before you capture the image. This cancels Multiview.

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

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.

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

This problem has been fixed in Celestia v1.4.1 and later, available on SourceForge: the Windows date/time input routine is no longer used.

September 1752 is when Great Britain and its colonies converted from the Julian calendar to the Gregorian calendar. This changed the day on which the new year started and also lost 11 days from that year.

Earlier versions of the Windows version of Celestia 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.

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

Briefly:

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

## Questions about objects (not) seen in Celestia

### Why are my favorite stars not in Celestia?

Celestia v1.3.2 includes only stars that had their distances measured by the Hipparcos satellite. Hipparcos was not used to measure the distances to many dim, variable or close double stars. Someone may have created an Add-on that includes your stars, though. Or consider creating the necessary STC file yourself and contributing it.

More recent versions of Celestia include all of the stars within 20 LY of the Sun, as well as about 200 double stars. (There are actually many more double stars than that, but relatively few have had their orbital parameters accurately measured.)

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

Their diameters are exactly right. As seen from the earth, they both are 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. Review of their book

A simple experiment was 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?

And Dalle of the Forum wrote

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.

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

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 investigators. The colors of those pictures aren't realistic at all.

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.

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

Hipparcos could only measure parallax to a value of about 1 milli-arc-second. For details, please read the thread [1] 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 [2], Chris wrote about some of the tradeoffs in the current version of Celestia.

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

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


Increase 100 to 500 or larger.

### 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?

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 -

1. There's no way Celestia can display "realistic" brightnesses on your computer screen; but
2. such "realism" is unnecessary because your eyes merely adapt to compensate.

(Provided by Grant Hutchison)

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

(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.

(Provided by Don G.)

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

If you're running Celestia v1.3.0 or later

1. Select the body from which to observe; e.g. type H then 3 to select Earth,
2. Use the GoTo menu to specify your Longitude and Latitude and GoTo there (lat & long are entered in decimal format - there are websites that convert to/from degrees/minute/seconds format, such as this one,)
3. Type y = Sync Orbit (this locks you into position above the location you set),
4. Type (Windows:Ctrl-G) (Linux:Alt-S) = Goto Surface,
5. Type (Windows:Ctrl-F) (Linux:Alt-F) = change Arrow keys to AltAzimuth mode (this keeps the horizon level when panning left & right),
6. Use the arrow keys to look toward the sky, you can adjust the field of view (FOV - how much sky you see at once) with the , & . keys.

Unfortunately, there is not (yet) an alt-az coordinate system display, but typing a ; will turn on the equatorial coordinate system display. There are some scripts which add alt-az display, such as Planetarium.

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

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.

Addendum provided Tech Sgt. Chen:

Mir, along with certain other spacecraft models, were modeled within an historical time frame and can only be viewed between the mission start and end dates. You can override ending dates by opening the solarsys.ssc or other specific craft related .SSC files and placing a pound sign (#) in front of the ending date string. Then save the new setting. This way you can always view your installed Space Crafts. Consequently, removing the pound sign will return the craft to its natural time frame.

### 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????

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.

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

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". Near the beginning it has a line that starts with "Max texture size:"

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 2K or 4K buffer. Microsoft's software version of OpenGL only has a 1K buffer.

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

The orbit of the International Space Station 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". [3]

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[4]

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. Another issue is that Celestia v1.5.1 and earlier use a fixed rotation speed for the Earth. Since the Earth's rotation is variable, the surface of Celestia's Earth is displaced from where it should be. Celestia v1.6 will use a more accurate variable rotation speed. In other words, you can't use Celestia to find out where to look in the sky to see the ISS.

### 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?

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.

Cel:// URLs run the copy of Celestia that is in the folder named Celestia. If you want to change back to using your old Celestia that way, just rename the directories again: rename Celestia to be Celestia132 and rename Celestia131 to be Celestia.

A description of how to organize your Addons so they can be moved easily.[5]

### I've compared the Celestia texture for Venus/Ida/Miranda with one I've found in a book or on the Web, and Celestia's map is upside down. What's going on?

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 (i.e. counterclockwise); or as a "retrograde" rotator, if it rotates in the opposite direction.

But 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.

(Provided by Grant Hutchison)

## What if I have more questions?

If you have a question about Celestia that is not answered above or elsewhere in this WikiBook, please ask your question in the Celestia Web Forum, not here. There are many experts reading the Forum, but very few knowledgeable people read the WikiBook. If a question is asked more than once or twice in the Forum, it'll be added to this FAQ.

## Introduction

This is a glossary of Celestia terminology. Many of the terms used with Celestia are very similar to the corresponding astronomical terminology. For a glossary of astronomical terms, see the Astronomical Terms: Appendix to the Wiktionary

## Glossary

### Barycenter

A (possibly moving) invisible position in space defined in an STC catalog file, around which other STC and SSC objects can orbit.

### catalog

A text file used to define objects and their positions. Different catalogs are used to define a Star (STC), a planetary system which orbits around a Star (SSC) and objects not associated with a Star (DSC).

### CMOD

Celestia MODel file: a proprietary format used to define a 3D object.

### DSC

Deep Space Catalog; used to define glowing Nebulae or Galaxies or invisible OpenCluster objects around which nothing can orbit. Celestia v1.6 adds Globular Clusters.

### EllipticalOrbit

One of several different types of periodic trajectories, defined using traditional Keplerian parameters. Used in STC and SSC catalog files.

### Galaxy

A glowing object defined in a DSC catalog file using a PNG template and astronomical coordinates.

### GlobularCluster

A spherical group of dots defined in a DSC catalog file using parameters which determine how tightly grouped the dots are.

### Hipparcos

An astrometric satellite and the database created from its observations; used to define the positions of more than 100,000 stars in Celestia.

### Horizons

JPL's on-line solar system data and ephemeris computation service. Often used to generate orbit and trajectory data files.

### Julian Date

Julian dates are a continuous count of days and fractions since noon Universal Time on January 1, 4713 BCE (on the Julian calendar). Almost 2.5 million days have transpired since this date. Julian dates are used in Celestia's SSC and STC catalogs for the fields Epoch, Beginning and Ending. These fields use 64-bit floating point (double precision) variables, and can represent a Julian date to about 1 millisecond of precision. The time scale that is the basis for Julian dates is Universal Time. Starting with v1.5, Celestia uses TDB internally and UT for its on-screen display. 0h UT corresponds to a Julian date fraction of 0.5: Julian days go from Noon to Noon instead of from Midnight to Midnight. This is so that the date doesn't change in the middle of nocturnal observations.

### Location

A Celestia object: defines a label for a position on a body.

### map

1. An image file providing information about the visual characteristics of an object.
2. A mathematical transform between the geometry of a spheroidal object and a flat surface. The mapping known as "simple cylindrical projection" or "Plate Carré" is used by Celestia to map between flat images (surface texture files) and spherical planets and moons.

### Mesh

1. A 3D model used to display an object with an arbitrary shape.
2. A list of connected vertices specified in a CMOD 3D model file.

### NAIF

NASA's Navigation and Ancillary Information Facility. A source for SPICE trajectory files.

### Nebula

A glowing or invisible object defined in a DSC catalog file by specifying a Mesh and astronomical coordinates.

### normal

1. A vector perpendicular to the surface at a position. I.e. a surface normal vector. Used to indicate irregularities and provide dynamic shading on surfaces.
2. conventional or standard surface texture; not an AltSurface.

### object

A body which has its appearance and position defined in a catalog.

### OpenCluster

A labeled, fixed position defined in a DSC catalog file. It is not necessarily associated with any particular glowing object.

### path

1. A line drawn on the screen to indicate the orbit or trajectory of an object.
2. The hierarchical list of objects around which the object currently being defined is orbiting.

### position

A place in a coordinate system. Not to be confused with a Location.

### ReferencePoint

A (usually moving) invisible position in space defined in an SSC catalog file, around which other SSC objects can orbit. A ReferencePoint has only positional characteristics. It cannot be used to provide any orientation information.

### SPICE

Spacecraft, Planet, Instrument, C-matrix and Events kernels; not to be confused with Simulation Program with Integrated Circuit Emphasis. A type of NASA trajectory information file. Use of SPICE ketnels was introduced in Celestia v1.5.0.

### SpiceOrbit

A trajectory defined using NAIF SPICE kernels.

### SSC

Solar System Catalog; used to define non-glowing objects which orbit around Stars, Barycenters and each other.

### Star

A glowing object defined in an STC catalog file, around which STC and SSC objects can orbit.

### STC

STar Catalog; used to define glowing Stars or invisible Barycenter objects around which other objects can orbit.

### trajectory

The positions traversed by a moving object.

### Universal Coordinate System

The default coordinate system used by Celestia is Ecliptic J2000:
The fundamental plane is the J2000 Earth ecliptic, and the preferred direction (x-axis) is the J2000 equinox.

# Enhancing Celestia

The following reference pages will help you to add features and make Celestia easier to use in your environment.

## Introduction

Typing commands on the keyboard can be tiring and error prone. If you are using Celestia to show the universe to others, a script may be an effective way to tour the stars.

## Types of Scripting

Celestia supports two different Scripting languages, CEL and CELX (Lua). These can be used to add new functionality to the program, or to run educational activities.

### CEL scripting

See the page Celestia/Cel_Scripting

### CELX scripting

See the page Celestia/Celx_Scripting

### Other Languages

You can use any other language you want if it can pass commands to the operating system's command interpreter. It can issue the command to run Celestia and can include on that command line the instruction 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:

./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: use two hyphens)

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


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