A (not so) Brief Introduction to Celestia Addons (3rd edition)

0:  Introduction.
1: General Overview.
2: A Simple Addon.
3: A Simple Nebula Addon.
4: Installing a Complex Nebula Addon.
5: Installing an Addon of Stars and Planets.
6: Common Addon Problems.
7: Installing Celestia.


Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.


---

See also:
• Addon Intro in separate pages (for use with Babelfish or other translators)
• Selden's List of Resources for Celestia

Note:

This Web page is too long to be completely translated by BabelFish. It is now available in shorter sections starting at http://www.lns.cornell.edu/~seb/celestia/addon-intro-p0.html

One of the best things about Celestia is that it provides ways for you to add many astronomical objects that are not included in Celestia's distribution kit. Once you learn how they work, I'm sure you'll find creating Addons to be a lot of fun. They're a lot of fun to look at, too.

The second edition of "Introduction to Addons" was updated for Celestia Version 1.3.0 (and later). Several new features are available which make it a lot easier to keep track of the Addons you've installed and to move them to the next version of Celestia. Older Addons still work, but if you're willing to change them a little, they'll be much easier to use and understand.

This third edition was updated to include a relatively simple Nebula Addon for NGC3372. It's more complicated than the star and planet Addon but not as demanding as Rassilon's Rosetta Nebula Addon. Also, a section has been included which tries to provide help for common problems.

Some of these example Addons describe imaginary objects. There really is a Rosette Nebula, but we really don't know its three-dimensional shape. Also, we know nothing about whatever planetary systems might be in it.

Most Addons consist of 1, 2 or 3 sets of files:

1.1: One or more Catalog files. These describe where the objects are in space.
1.2: Surface pictures (texture maps) for those objects. These give the objects a unique appearance.
1.3: Models of the objects. These give them special shapes.


1.4: File locations. Each type of file goes into a particular directory.


---

1.1: One or more Catalog files describing where the objects are in space.

• .SSC (Solar System Catalog) files tell Celestia where to draw planets.
• .STC (STar Catalog) files tell Celestia where to draw stars.
• .DSC (Deep Space Catalog) files tell Celestia where to draw Nebulas, OpenClusters and Galaxies.

  Although they're all plain text files, different keywords are used in the different types of Catalog files. You can't rename a .SSC file to be a .STC file, for example.

  The first part of a Catalog file's name doesn't matter. Celestia tries to load all of the .SSC, STC and DSC files that it finds. The first part of the name is to help you keep track of which file is for what.

  Celestia only reads in Catalog files when it starts up. If you modify an old file or add a new Catalog file, you have to exit from Celestia and start it up again so it can find the new file.

  Unfortunately, some Addons don't include a Catalog file. Their authors leave it up to you to create one.

  Celestia includes its own SSC file that defines all of the planets and many of their moons, along with asteroids, comets and a few spacecraft. This is the file named solarsys.ssc in Celestia's data directory. Some Addons provide better surface textures for objects in our solar system. If you're careful to make a copy, you can modify solarsys.ssc to use one or more of these textures instead of the ones provided with Celestia.

  See also "Creating and using .SSC files".

---

1.2: Surface pictures (texture maps) for those objects, giving them a unique appearance.

Lots of people enjoy making replacement surface textures for existing planets or moons. For them, you either have to rename the image files to match the ones specified in the appropriate .SSC file, or you have to edit the .SSC file so it looks for the name of the new surface texture file.

Celestia comes with many surface textures already in the lores and medres directories, although it doesn't come with any hires images. It's best not to mix your images among those that Celestia uses. Use a separate subdirectory instead. See Section 1.4 below.

See also "Creating Textures for Celestia".

---

1.3: Models of the objects, which give them special shapes.

Objects with complicated structures can be created using a 3D design package. Celestia can understand models that are defined in the 3DS file format. This format was originally used by the 3D modelling software named "3D Studio Max". Most 3D design programs can create 3DS files if you use their "Export" command.

Models can be designed either to require particular surface texture files or to accept a surface texture specified by Celestia. When surface textures are specified in a model, Celestia loads them from a textures\medres directory.

---

1.4: File locations. Each type of file goes into a particular directory.

Celestia v1.3.0 (and later) lets you organize your Addon files. Previous versions of Celestia required that the files be mixed in with the ones that come with Celestia. As a result, many older Addons put their files into the directories that Celestia uses itself: extras, models, and textures This causes lots of confusion when you install a new version of Celestia.

Starting with Celestia v1.3.0, Addon files can go into a separate Celestia subdirectory (folder) that you create within Celestia's extras directory. Now when you install a new version of Celestia, you can simply drag that whole Addon directory into the extras directory of the new version of Celestia. You no longer have to keep track of which files you added, which ones belong to which Addon, and which came with Celestia.

Here's one way to organize Addons:

• Create a directory (folder) within Celestia's extras directory which has the name addons. This will let you move all of your Addons at once by moving just this one directory.
• Within the addons directory, create a directory for each Addon when you install it. For example, you might create the NGC2237 directory.
• Within the NGC2237 directory, you must create the directories for its models and its surface textures: create the directories models and textures. Within the textures directory, create the directories lores, medres and hires.

  When you've finished, your directory structure might look something like this:

  ---

  [-] Celestia130
      --- data
      [-] extras
       |  [-] addons
       |      [+] HIP500000
       |      [-] NGC2237
       |          --- models
       |          [-] textures
       |              --- hires
       |              --- lores
       |              --- medres
      --- models
      [+] textures
  

  ---

• Catalog files all go into an Addon's main directory. For example, the STC and SSC Catalogs for NGC2237 should go into the directory NGC2237 itself.

  An older Addon, one which was created before this new directory layout became possible, usually includes an \extras\ directory containing all of its catalog files. Those files all must be moved into the Addon's main directory and the folder \extras\ that was provided with the Addon should be deleted.

• Most Addons come with just one texture resolution. Their pictures all go into the medres directory. For example, NGC2237.png should go into the directory NGC2237\textures\medres.
  Texture images for planets and moons can go into any of the subdirectories lores, medres or hires that are in a Celestia subdirectory named textures.

  If there is only the one texture file with a unique name, Celestia will look in all three directories while trying to find it.

  If there are texture files with the same name in more than one of the textures subdirectories, you can toggle among them using the "r" and "R" keyboard commands.

• 3DS model files go into a subdirectory named models. For example, NGC2237.3ds goes into the directory NGC2237\models.

  When a 3DS model specifies texture maps in the model itself, those texture files must go into the medres directory. Celestia does not yet provide a way to select different resolution surface textures in this case.

You might want to start simply and add pieces one at a time so you can see how they work together. From little acorns mighty oaks do grow :-)

This Addon consists just of a star with a single planet orbiting around it. It uses a Star Catalog and a Solar System Catalog.

For this and other Addons to work properly, you should download and install Celestia v1.3.0 (or a newer version) if you haven't already done so. Many Addons require this newer version of Celestia in order to work. Nebula definitions, for example, can't work with version 1.2.5. See section 7 for details.

As the first step in this Addon, create the directory \extras\addons\HIP500000\ (That's "HIP5" followed by 5 zeros.)

Your directory structure might look something like this:

---

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      --- HIP500000
    --- models
    [+] textures

---

(The HIP500000 directory does not need any subdirectories. The surface texture this Addon uses is one that comes with Celestia.)

Within the HIP500000 directory, create two Catalog files:
2.1: A STar Catalog (STC), which tells Celestia where to draw the star.
2.2: A Solar System Catalog (SSC), which tells Celestia where to draw planets around the star.

---

2.1: An STC file

Celestia uses "Hipparcos numbers" to keep track of stars. Hipparcos numbers are numbers assigned by the astronomers who used the Hipparcos satellite to measure the distances to many stars.

Imaginary stars have to be given fake Hipparcos numbers in Celestia. Usually people use numbers between 300000 and 600000.

Here is a very simple STC file which defines the star named "HIP 500000".

Put this STC file into the directory \extras\addons\HIP500000\

This STC file contains the information Celestia needs to draw a star. However, Celestia ignores everything on a line after the #. Those are "comment lines".

If you type this in by hand, be sure to get the Capitals and spaces right. "{" and "}" are the letters "shift-[" and "shift-]" These squiggly-brackets are important: they tell Celestia where the definition of each object begins and ends. I usually use "Select-and-Paste" commands so I know everything got copied exactly right.

---

#######################
#hip500000.stc
#######################
# HIP 500000
500000 {		#Hipparcos number of star
	RA  98.0	#Right Ascension of star, measured in degrees
	Dec  5.04	#Declination of star
	Distance  5500	#Distance to star, measured in Light Years
	SpectralType "G0"	#may also include its Luminosity Class
	AppMag 15	#Apparent Magnitude of star as seen from Earth
} 
#######################

---

Alternatively, here's a link to a copy of this file that you can download:
• hip500000.stc

---

Sidebar:

If you're using Celestia v1.3.0, its STC files can only include the Hipparcos index number. Names have to be added to the file starnames.dat.

If you're using Celestia v1.3.1pre3 or newer, its STC files can include both a star's Hipparcos index number and its name.

The star's name must follow the Hipparcos number, be enclosed in quotes, and come before the first "{". More than one name can be specified between the quotes if they're separated by colons (:).

For example, here's how you could define Intro as the name for the star HIP 500000:

---

#######################
#hip500000.stc
#######################
# HIP 500000
500000 "Intro" {	#Hipparcos number and name of star
	RA  98.0	#Right Ascension of star, measured in degrees
	Dec  5.04	#Declination of star
	Distance  5500	#Distance to star, measured in Light Years
	SpectralType "G0"	#may also include its Luminosity Class
	AppMag 15	#Apparent Magnitude of star as seen from Earth
} 
#######################

---

---

Now start Celestia and type the commands
[return]
HIP 500000[return]

• HIP can be spelled hip -- capitals don't matter here.
• One space between HIP and the number is needed to match the number declared in the .STC file.
• [return] stands for the large "Carriage-Return" key at the right edge of the main part of your keyboard. Sometimes it's labelled "Enter".
• When you type the first [return], Celestia will prompt with "Target name:". It wants you to type the name of the object to be "Selected". You can type just another [return] if you don't want to change the selection.

This star name (HIP 500000) should appear in the top left corner of Celestia's window. This means that the star is "Selected".

If this does not happen, there may be some mistakes in the STC file you made, or you might have put it in the wrong folder. Look at it very carefully. Capitals matter. Quotes (") matter. Don't add spaces in the middle of the command words.

Now type a "G" to GoTo that star. Celestia should turn and go flying to it. You should see a brightly glowing star just like our Sun, with sunspots but no planets.

Exit from Celestia.

---

2.2: An SSC file

Here is a very simple SSC file. It defines the planet named "b" orbiting around the star "HIP 500000".

Put this .SSC file into the directory \extras\addons\HIP500000\ where you already put hip500000.stc.

This .SSC file only includes the barest minimum of declarations that Celestia really needs for it to draw a planet. All of the other things that people put into .SSC files just make a planet look better or make it follow precisely the orbit that astronomers have measured.

The lines starting with a # are not needed. They're known as "comment lines." Everything on a line following a # is ignored by Celestia.

If you type this file in by hand, be sure to get the Capitals and spaces right. "{" and "}" are the letters "shift-[" and "shift-]" These squiggly-brackets also are important: they tell Celestia where the definition of each object begins and ends. I usually use "Select-and-Paste" commands so I know everything got copied exactly right.

---

#########################
# hip500000.ssc
#########################
"b" "HIP 500000" {
	Texture "jupiterlike.jpg"
	Radius 64000 
	EllipticalOrbit
	{	Period 5.8
		SemiMajorAxis 2.5
	}
}
#########################

---

Alternatively, here's a link to a copy of this file that you can download:
• hip500000.ssc

Now your directory structure should look something like this:

---

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      --- HIP500000
     |           -- hip500000.ssc
     |           -- hip500000.stc
    --- models
    [+] textures

---

Start Celestia.
GoTo HIP 500000 as you did in step 2.1 above.

Open the menu "Navigation" "Solar System Browser" after you GoTo the star. It should list all of the planets around the star: just "b" in this case.

GoTo the planet. Play with the Render settings.

Here's a snapshot taken by Celestia of this solar system: HIP 500000 and its planet "b"

and here's a Cel://URL to take you to this viewpoint: HIP 500000 and its planet "b"

Here is an example for installing a relatively simple Nebula Addon.

I'll assume you're using some version of Windows, although equivalent operations should work with the MacOS X and Linux versions of Celestia.

If you've ever downloaded and installed other software, I'm sure this description will be full of things you already know how to do. You should be able to use similar procedures for other Addons.

Essentially, the steps are:

3.1: Download the Zip archive file containing the Addon you want
3.2: Create the directory tree to contain the Addon.
3.3: Copy the Addon files from the zip archive to the appropriate Celestia directories
3.4: Start Celestia and view the object.

In detail:

---

3.1: Download NGC3372

If you haven't already, download the zip archive containing a simple Eta Carinae Nebula Addon. This nebula is also known as NGC 3372.
• ngc3372.zip (230KB)

  ---

  Archive:  ngc3372.zip
  
    Length     Date   Time    Name
   --------    ----   ----    ----
          0  10-07-03 19:23   ngc3372/
        217  10-07-03 19:19   ngc3372/eta-car-130.stc
        236  10-07-03 19:19   ngc3372/eta-car.stc
          0  10-07-03 19:23   ngc3372/models/
        709  10-07-03 16:05   ngc3372/models/ngc3372.3ds
       1565  10-07-03 19:23   ngc3372/ngc3372-readme.txt
        534  10-07-03 16:03   ngc3372/ngc3372.dsc
          0  10-07-03 19:23   ngc3372/textures/
          0  10-07-03 19:23   ngc3372/textures/medres/
     241637  04-13-03 15:49   ngc3372/textures/medres/ngc3372.jpg
       5120  10-07-03 19:18   ngc3372/textures/medres/Thumbs.db
   --------                   -------
     250018                   11 files

  ---

---

3.2: Create the directory tree for NGC3372, if necessary

If you use an unZip program to restore the entire archive, it should automatically create the necessary directories. Alternatively, if you have a "visual" unZip program, you can drag the NGC3372 folder out of the Zip archive into your Addons folder. That single operation will recreate all of the folders and files in the right places.

If you want, however, you can create all of its directories by hand and then drag the files individually from the archive into them. Here are the details of this manual procedure:

1. If you haven't already done so, create a directory (folder) within Celestia's extras directory which has the name addons. This will let you move all of your Addons at once by moving just this one directory.

2. Within the addons directory, create a directory for each Addon when you install it. For example, you might create the NGC3372 directory.

3. Within the NGC3372 directory, you must create the directories for its models and its surface textures: create the directories models and textures Within the textures directory, create the directory medres. (The lores and hires directories aren't needed for this particular Addon.)

When you've created the new directories, your directory structure might look something like this:

---

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      [+] HIP500000
     |      [-] NGC3372
     |          --- models
     |          [-] textures
     |              --- medres
    --- models
    [+] textures

---

---

3.3: Copy Addon files

Here's the "difficult" drag-and-drop method of installing the Addon. You also can have Zip extract and install the files directly into the appropriate subdirectories, but the steps below will help you understand what's supposed to happen.

You need to have a ZIP program installed to extract the files. (Windows XP comes with one built in.)

• Double click on the Zip archive file NGC3372.ZIP. A new unZip window should open showing the files that are in the archive.

  This Addon has 4 components:

  1. A Deep Space Catalog desribing the Nebula NGC 3372, ngc3372.dsc,
  2. A STar Catalog desribing Eta Carinae, eta-car.stc,
  3. A 3DS model to hold the picture of NGC 3372, ngc3372.3ds, and
  4. A JPEG picture of the nebula, ngc3372.jpg.

  All of the Catalog files for an Addon, whether they're .STC, .DSC or .SSC, go into the same "root" directory.

  3.3.1: The Deep Space Catalog

  In the Zip archive, locate the file ngc3372.dsc. This is the "Deep Space Catalog" which defines the Nebula's name and location, the model to use and the nebula's size. Drag it to the Celestia subdirectory extras\addons\NGC3372\

  or you can use this copy:

  ---

  ######################
  # NGC 3372
  #
  # The accompanying image of NGC3372 was derived from 02192.TIFF
  # at http://www.noao.edu/image_gallery/html/im0061.html
  # Original tiff image credit:
  # "National Optical Astronomy Observatory/
  # Association of Universities for Research in Astronomy/
  # National Science Foundation" 
  # 
  Nebula "NGC 3372" {
      Mesh     "ngc3372.3ds"
   	Axis [-0.206916 0.153726 0.966206]
  	Angle 154.5
  	Distance   8500
  	RA      10.7345 
  	Dec      -59.752
  	Radius     219
          InfoURL "http://www.noao.edu/image_gallery/html/im0061.html"
      }
  ######################
  

  ---

  Alternatively, here's a link to a copy of this file that you can download:

  • ngc3372.dsc (1KB)

  3.3.2: The STar Catalog

  In the zip archive, locate the files eta-car.stc and eta-car-130.stc. These are "STar Catalogs". They define the incredibly bright variable star Eta Carinae which illuminates the nebula. eta-car-130.stc should be used with Celestia v1.3.0. If you have a later version, like a prerelease of Celestia v1.3.1, then you should use the file eta-car.stc. Drag the appropriate STC file to the Celestia subdirectory extras\addons\NGC3372\. or you can use this copy:

  ---

  # Eta Carinae -- a high luminosity irregular variable
  500002 "Eta Car:HD 93308" {
  	RA 	161.264958
  	Dec 	-59.684517
  	Distance  8500
  	SpectralType "O5Ia"
  	AppMag 7.0
  	InforURL "http://www.seds.org/messier/xtra/ngc/etacar.html"
  }
  

  ---

  Alternatively, here's a link to a copy of this file that you can download:

  • eta-car.stc (0.5KB)

  Remember: if you're going to use this file with v1.3.0 of Celestia, then you'll have to delete the starnames from the .STC file. The quoted string "Eta Car:HD 93308" needs to be removed. See the sidebar above in section 2.1.

  3.3.3: The 3DS Model

  In the zip archive, locate the file ngc3372.3ds This is the 3D shape model for the picture of the nebula. Drag this 3DS model to the Celestia subdirectory extras\addons\ngc3372\models

  Alternatively, here's a link to a copy of this file that you can download:

  • ngc3372.3ds (1KB)

  Note that this model doesn't define a complicated 3D shape for the nebula itself. Instead, it's just a thin rectangular block for holding a photograph of the nebula. To learn how to use "billboards" to display astronomical photographs in Celestia, please see billboard.html.

  3.3.4: The Surface Texture Image

  In the zip archive, locate the file ngc3372.jpg This is a JPEG picture of the Nebula. Drag it to the Celestia subdirectory extras\addons\ngc3372\textures\medres\ (All image files used by models must be in the medres directory.)

  Alternatively, here's a picture of the surface texture image which links to a copy of the texture.

  
  NGC 3372 (241KB)

  Note that this surface texture image is an opaque picture of the Nebula and its surrounding stars. Often artists designing deep space models for Celestia remove the stars from the astronomical photographs of the objects. They then provide .STC files specifying the types and locations of many of the stars near the Nebula. The surface textures they provide usually include an Alpha transparency channel, too, which makes the nebulosity translucent. None of these things have been done for this simple example.

  Now your directory structure should look something like this:

  ---

  [-] Celestia130
      --- data
      [-] extras
       |  [-] addons
       |      [+] HIP500000
       |      [-] NGC3372
       |           -- eta-car.stc
       |           -- ngc3372.dsc
       |          --- models
       |               -- ngc3372.3ds
       |          [-] textures
       |              --- medres
       |                   -- ngc3372.jpg
      --- models
      [+] textures
  

  ---

---

3.4: Start Celestia.

1. Check to make sure you're running v1.3.0 or newer: open the "Help" menu and select "About Celestia". A new window will open that has the name "Celestia" and its version number at the top-center. The version number should be 1.3.0 or greater. If it's 1.2.n then the Nebula Addon can't work. If you've been copying the files to the wrong Celestia directory, you can just drag your new "Addons" directory to the right directory.

2. Test to see if Celestia knows the Nebula's name. To do this, type the following sequence of commands:
[return] (Celestia will prompt with "Target name: " )
NGC 3372[return]
   (Be sure to type a space between NGC and 3372. The name you type here must be exactly the same as is defined in ngc3372.dsc.)

   If the .DSC file is OK, then the name will appear in the upper left corner of Celestia's window along with the distance (8500 ly). You have now "selected" NGC 3372.

3. Now, make sure galaxy rendering is enabled:
   • Select the "Render" menu
   • Select the "View Options" item
   • In the new window:
     • check (select) the Show "Galaxies" box
     • also check (select) the Label "Galaxies" box
     • then select the [OK] button (NOT the [x] box at the top right)

4. Type the letter "c". Celestia will turn toward the selected object. That's NGC3372 in this case. Celestia should pause briefly while it loads the model and its texture. When the viewpoint finally stops turning, you should see a purple-red blotch in the middle of the screen labeled "NGC3372" in yellow.

   If there's no yellow label, then you did not manage to select the "Label Galaxies" box. The "Show Galaxies" box probably isn't selected either. Go back to the "Render" "View Options..." menu and make sure their boxes are checked. You should see the label appear immediately when its box is checked. When you click on [OK], the label will stay while the menu goes away. If you click on [x] at the upper right, the label will go away when the menu does because Celestia will forget the Render changes you just made.

   If there is a yellow label but no purple blotch, then either you didn't select "Show Galaxies" (type a "u" a couple of times to toggle "Show Galaxies") or Celestia can't find the model or its surface texture image.

   Please look at Section 6 for a list of some of the most common problems and possible solutions.

5. Then type the letter "g". Celestia will take you to a position near the nebula.
6. Enjoy!

   Here's a snapshot taken by Celestia of this nebula. Earth in NGC 3372

   and here's a Cel://URL to take you to this viewpoint: Earth in NGC 3372

Here is an example for installing a more complicated Addon.

Again, I'll assume you're using some version of Windows.

If you've ever downloaded and installed other software, I'm sure this description will be full of things you already know how to do.

These instructions are specifically for the Rosetta Nebula that Rassilon created. You should be able to use a similar procedure for equivalent creations.

Essentially, the steps are:

4.1: Download the Zip archive file containing the addon you want
4.2: Create the directory tree to contain the Addon.
4.3: Copy the Addon files from the zip archive to the appropriate Celestia directories
4.4: Start Celestia and view the object.

In detail:

---

4.1: Download NGC2237

If you haven't already, download the Rosetta Nebula Addon. The Rosette (or Rosetta) Nebula is also known as NGC2237.

Rassilon's downloads are in the directory http://63.224.48.65/~rassilon/. The Rosetta Nebula Addon is at http://63.224.48.65/~rassilon/NGC2237.zip or you can browse the Web page to select it.

---

4.2: Create the directory tree for NGC2237

• If you haven't already, create a directory (folder) within Celestia's extras directory which has the name addons. This will let you move all of your Addons at once by moving just this one directory.

• Within the addons directory, create a directory for each Addon when you install it. For example, you might create the NGC2237 directory.

• Within the NGC2237 directory, you must create the directories for its models and its surface textures: create the directories models and textures Within the textures directory, create the directory medres. (The lores and hires directories aren't needed for this particular Addon.)

  When you've created the new directories, your directory structure might look something like this:

  ---

  [-] Celestia130
      --- data
      [-] extras
       |  [-] addons
       |      [+] HIP500000
       |      [-] NGC2237
       |          --- models
       |          [-] textures
       |              --- medres
      --- models
      [+] textures
  

  ---

---

4.3: Copy Addon files

Here's the "difficult" drag-and-drop method of installing the Addon. You also can have Zip extract and install the files directly into the appropriate subdirectories, but the steps below will help you understand what's supposed to happen.

You need to have a ZIP program installed to extract the files. (Windows XP comes with one built in.)

• Double click on the Zip archive file NGC2237.ZIP. A new unZip window should open showing the files that are in the archive.

• In the Zip archive, locate the file "NGC2237.dsc" This is the "Deep Space Catalog" which defines the Nebula's location, the model to use and its size. Drag it to the Celestia subdirectory extras\addons\NGC2237\

  or you can use this copy:

  ---

  ######################
  # ngc2237.dsc
  ######################
  Nebula "NGC2237" {
          Mesh "ngc2237.3ds"
          RA   6.5383
          Dec  5.05
          Distance  5500
          Radius  75
  }
  ######################
  

  ---

  Alternatively, here's a link to a copy of this file that you can download:

  • ngc2237.dsc

• In the zip archive, locate the files NGC2244.stc and NGC2244-2.stc in the \extras\ folder. These are "STar Catalogs". They define a cluster of stars in the middle of the nebula. Drag them to the Celestia subdirectory extras\addons\NGC2237\. (All Catalog files for a specific Addon go into the same "root" directory)

• In the zip archive, locate the file NGC2237.3DS This is the 3D shape model for the nebula. Drag it to the Celestia subdirectory extras\addons\NGC2237\models

• In the zip archive, locate the file rosetta.png This is a PNG picture that is used to provide surface coloration for the model. It determines the colors and the transparency of the various regions of the nebula. Drag it to the Celestia subdirectory extras\addons\NGC2237\textures\medres\ (All image files used by models must be in the medres directory.)

  Now your directory structure should look something like this:

  ---

  [-] Celestia130
      --- data
      [-] extras
       |  [-] addons
       |      [+] HIP500000
       |      [-] NGC2237
       |           -- NGC2237.dsc
       |           -- NGC2244.stc
       |           -- NGC2244-2.stc
       |          --- models
       |               -- NGC2237.3ds
       |          [-] textures
       |              --- medres
       |                   -- rosetta.png
      --- models
      [+] textures
  

  ---

  Note: NGC2237.ZIP includes an \extras\ directory which contains all of its catalog files. Those files all must be moved into the Addons directory itself, \NGC2237\, and the folder \NGC2237\extras\ should be deleted. This is an older Addon which was created before the new directory layout became possible.

---

4.4: Start Celestia.

1. Check to make sure you're running v1.3.0 or newer: open the "Help" menu and select "About Celestia". A new window will open that has the name "Celestia" and its version number at the top-center. The version number should be 1.3.0 or greater. If it's 1.2.n then the Nebula Addon can't work. If you've been copying the files to the wrong Celestia directory, you can just drag your new "Addons" directory to the right directory.

2. Test to see if Celestia knows the Nebula's name. To do this, type the following sequence of commands:
[return] (Celestia will prompt with "Target name: " )
NGC2237[return]
   (Don't type a space between NGC and 2237. The name you type here must be exactly the same as is defined in NGC2237.dsc.)

   If the .DSC file is OK, then the name will appear in the upper left corner of Celestia's window along with the distance (5500.000 ly). You have now "selected" NGC2237.

3. Now, make sure galaxy rendering is enabled:
   • Select the "Render" menu
   • Select the "View Options" item
   • In the new window:
     • check (select) the Show "Galaxies" box
     • also check (select) the Label "Galaxies" box
     • then select the [OK] button (NOT the [x] box at the top right)

4. Type the letter "c". Celestia will turn toward the selected object. That's NGC2237 in this case. Celestia should pause briefly while it loads the model and its texture. When the viewpoint finally stops turning, you should see a tiny pink blotch in the middle of the screen labeled "NGC2237" in yellow.

   If there's no yellow label, then you did not manage to select the "Label Galaxies" box. The "Show Galaxies" box probably isn't selected either. Go back to the "Render" "View Options..." menu and make sure their boxes are checked. You should see the label appear immediately when its box is checked. When you click on [OK], the label will stay while the menu goes away. If you click on [x] at the upper right, the label will go away when the menu does. Celestia will forget the Render changes you just made.

   If there is a yellow label but no pink blotch, then either you didn't select "Show Galaxies" (type a "u" a couple of times to toggle "Show Galaxies") or Celestia can't find the model or its surface texture image.

   Please look at Section 6 for a list of some of the most common problems and possible solutions.

5. Then type the letter "g". Celestia will take you to a position near the nebula.
6. Enjoy!

   Here's a snapshot taken by Celestia of this nebula. The constellation of Orion is to the lower right. NGC 2237 as seen from Io

   and here's a Cel://URL to take you to this viewpoint: NGC 2237 as seen from Io

   After you've used this URL to see where the nebula is on the sky, one thing you can do is to hold down the "," (comma) key to increase the magnification of Celestia's "telescope". You can turn it up until the nebula fills the screen!

These instructions are specifically for the second, larger, Rosetta Nebula Addon that Rassilon created. You should be able to use a similar procedure for equivalent creations.

Many of Rassilon's creations are available on the Web at http://63.224.48.65/~rassilon/. This particular Addon is available at http://63.224.48.65/~rassilon/NGC2244-systems_i.zip. NGC 2244 is the designation for the Open Cluster of stars in the middle of the Rosette Nebula. The Nebula itself is NGC 2237.

This Addon was designed assuming that you already have installed the Addon described in section 4 above as well as a "Globular Cluster" generator. Installing this Addon by itself has some potential problems which can be used to illustrate how Celestia supports Addons.

Katalina is Rassilon's name for an imaginary star which is the primary content of this Addon. This star name needs to be made known to Celestia. Briefly, the following steps will make that happen:

4.1: Edit \data\starnames.dat so it includes the star's name.

Note: If you have a version of Celestia released after v1.3.0, like v1.3.1pre3, you don't need to modify starnames.dat. You can include the star's name in the STC file itself.

4.2: Create the directory tree for \extras\addons\NGC2244\ (This makes it easy to keep track of NGC2244's pieces.)

4.3: Create \extras\addons\NGC2244\katalina.stc. (This tells Celestia where to draw the star.)

4.4: Copy NGC2244-katalina.ssc from the Zip file to the folder \extras\addons\NGC2244\ (This describes all the planets around the star.)
4.5: Copy all of the picture files that are in the Zip file in the directory \textures\medres\ to \extras\addons\NGC2244\textures\medres\.
(These images of the planets' surfaces are the artwork that Rassilon spent a lot of his time creating.)

Then you can GoTo the star by name and see its planets.

---

Below are the details for steps 4.1, 4.2 and 4.3. Steps 4.4 and 4.5 are the same as for any of the other ZIP files so I won't write about them here.

---

4.1: Editing starnames.dat

If you have Celestia v1.3.1pre3 or later, you can skip this step.

First some background:

Rassilon defined the planets that orbit around Katalina in the file NGC2244-katalina.ssc, and he used the star name "Katalina" everywhere in that file. So that name has to be taught to Celestia.

Celestia uses "Hipparcos numbers" to keep track of stars. Hipparcos numbers are numbers assigned by the astronomers who used the Hipparcos Satellite to measure the distances to many stars.

Imaginary stars like Katalina have to be given fake Hipparcos numbers in Celestia. Usually people use numbers between 300000 and 600000.

In order for Celestia to know which star number has which name, both its number and its name have to be added to Celestia's file \data\starnames.dat.

starnames.dat is a text file. It doesn't have any special binary codes in it. As a result, you can use either Notepad or Wordpad to edit starnames.dat.

Wordpad is usually a better choice because starnames.dat doesn't use the standard Windows method of using the two characters [carriage-return] [line-feed] to separate lines from one another. It just has [line-feed] between the lines, and so Notepad doesn't show the file right.

Be careful. though. Celestia gets all of its starnames from starnames.dat. You might want to copy it somewhere else to save it in case it gets damaged. You can copy back the one you saved if something goes wrong.

As Rassilon wrote in the README in the Zip file, you have to add this next line to the very end of \data\starnames.dat:
500506:Katalina

You can use the START menu, RUN item to start Wordpad and then use Wordpad's "file open" menu to get to starnames.dat

---

4.2: Creating the directory tree for NGC2244

• If you haven't already, create a directory (folder) within Celestia's extras directory which has the name addons. This will let you move all of your Addons at once by moving just this one directory.

• Within the addons directory, create a directory for each Addon when you install it. For example, you might create the NGC2244 directory.

• Within the NGC2244 directory, you must create the directories for its models and its surface textures: create the directories models and textures Within the textures directory, create the directory medres. (The lores and hires directories aren't needed for this particular Addon.)

When you've created the new directories, your directory structure might look something like this:

---

[-] Celestia130
    --- data
    [-] extras
     |  [-] addons
     |      [+] HIP500000
     |      [+] NGC2237
     |      [-] NGC2244
     |          --- models
     |          [-] textures
     |              --- medres
    --- models
    [+] textures

---

Note: NGC2244-systems_i.ZIP includes an \extras\ directory which contains all of its catalog files. Those files all must be moved into the Addons directory itself, \NGC2244\, and the folder \NGC2244\extras\ should be deleted. This is an older Addon which was created before the new directory layout became possible.

---

4.3: Creating the STC file

In order for Celestia to draw a star, you need an .STC (STar Catalog) file that tells Celestia where that star is and what it looks like.

Rassilon buried the definition for the star 500506 in the middle of one of his very big star catalogs. The Readme says you can delete those catalogs if you don't have his Globular Cluster Addon. But if you do that, you can't find Katalina.

Here's a simple .STC file that defines just the star that is named Katalina. Create this file in the directory \extras\addons\NGC2244\. You can use your favorite editor to create it. Notepad is fine. Wordpad is OK, too.

---

#######################
#katalina.stc
#######################

# HIP 500506
500506 {
	RA  98.02484576
	Dec  5.04107509
	Distance  5500.3959
	SpectralType "G0Ia-O"
	AppMag 15.00 # Radii: 1.47270096432767
} 
#######################

---

Alternatively, here's a link to a copy of this file that you can download:
• katalina.stc

---

Note:

If you're using Celestia v1.3.0, its STC files can only include the Hipparcos index number. Names have to be added to the file starnames.dat.

If you're using Celestia v1.3.1pre3 or later, its STC files can include both a star's Hipparcos index number and its name.

The star's name must follow the Hipparcos number, be enclosed in quotes, and come before the first "{". More than one name can be specified between the quotes if they're separated by colons (:).

For example, here's how you could define Katalina as the name for the star HIP 500506:

---

500506 "Katalina" {

---

Once you've changed starnames.dat, created katalina.stc, and put the other files in the right directories, your directory structure should look something like this:

---

[-] Celestia130
    --- data
     |  -- starnames.dat
    [-] extras
     |  [-] addons
     |      [+] HIP500000
     |      [+] NGC2237
     |      [-] NGC2244
     |           -- katalina.stc
     |           -- NGC2244-katalina.ssc
     |          --- models
     |               -- ngc2237-aster_i.3ds (Rassilon made a typo here)
     |          [-] textures
     |              --- medres
     |                   -- ngc2244-katalina_i.jpg
     |                   [...]
     |                   -- ngc2244-moon_i-bump.jpg
    --- models
    [+] textures

---

Now you finally should be able to run Celestia and use the commands
[return]
katalina[return]
c
g

to visit Rassilon's Katalina system in the heart of the Rosetta Nebula.

Here's a snapshot taken by Celestia of the Katalina solar system. The Katalina solar system.

and here's a Cel://URL to take you to this viewpoint: The Katalina solar system.

Here are some of the most common problems I've seen:
1. Nebulas are invisible because Galaxy drawing is disabled
   Solution: Type the letter "u" a few times. This should turn the Nebula picture on and off again. The Nebula and Celestia's grey galaxy blobs will always be visible at the same time. If you can't see the grey galaxy blobs, you won't be able to see any Nebulae, either.

2. Nebulas are invisible or planet surfaces are blank because the Addon's catalogs are in an \extras\ folder. This causes Celestia to look for the models and textures in the wrong places.
   Solution: Move the catalog files out of that \extras\ folder into the Addon's main folder.

   For example, all of the files that are in \NGC2237\extras\ must be moved into \NGC2237\ itself. Then delete the now-empty \NGC2237\extras\ folder.

   Originally Addons had to put their files in among the files that come with Celestia. The Zip file of one of these older Addons contains an \extras\ folder which corresponds to Celestia's own \extras\ folder. It contains the Addon's catalogs. Celestia v1.3.0 and later is confused by this and will look in the wrong place for the models and surface texture images.

3. Nebulas are invisible or planet surfaces are blank because there are spelling errors in the names of the directories.
   Typographical errors are annoying. I don't know how many times I've stared at a directory name and not noticed that it's spelled wrong.

4. Nebulas are invisible or planet surfaces are blank because the image or model files are in the wrong directories.
   My hand-eye coordination isn't the best. I often manage to drag them into a folder that's nearby, but not the right one.

5. Nebulas are invisible because "Limiting Magnitude" is set too low.
   Type the character "]" a few times to increase it. "[" will turn it down again. The Limiting Magnitude has to be 2.0 or more for Nebula pictures and galaxies to be drawn.

6. Objects defined with 3DS models are invisible because the model file is specifying a different surface texture image file name.
   If you have a binary file editor like HexEdit, you might try editing the 3DS file to find out exactly what texture it's looking for. You could try changing it to use another texture to find out if the problem is related to the image file.

   Also, if you're running Linux, the case of the letters in the file's name matters. The case of the letters has to be exactly the same in the 3DS file as is used for the filename itself. Linux is case-sensitive, but Windows is not. As a result, some Addons which work fine under Windows fail under Linux. It's safest to change the name of the surface texture image file(s) to be exactly the same as is specified in the 3DS model. It's essentially impossible to fix a damaged 3DS model, but easy to rename a file.

7. Nebulas are invisible or planet surfaces are blank because your graphics card has run out of graphics memory.
   If your 3D graphics card has limited memory (32MB or less) then you have to be careful not to look at many other objects before trying to look at a new one. Celestia does not flush "old" images from the memory on the card. If there's no room, the surface texture pictures for the new objects won't be loaded. As a result, Nebula objects may be invisible. One possible workaround is to disable the "medres" planetary images provided with Celestia. One way this can be done is to rename the folder \Celestia\textures\medres\ to be \Celestia\textures\nomedres\.

8. Nebulas are invisible or planet surfaces are blank because their surface texture images have the wrong sizes.
   If you're creating a Nebula or planetary map, you may have mis-sized its surface texture image. It needs to be a power of two on a side: e.g. 1024x512.

Several versions of Celestia, including v1.3.0, are available at http://sourceforge.net/project/showfiles.php?group_id=21302

If you have an older, slower system or use a dialup modem, then you might want to download the 5.5MB lores version of Celestia instead of the 11MB medres version. The only difference is in the size of the images used for the surfaces of the planets and moons. The lores images will be somewhat blurrier.

Download the .EXE file of the installer for the version of Celestia that you want. Then run it. That starts the installation program. The installation software will let you put Celestia anywhere you want. It's usually a bad idea to put it in the same directory where you have a previous verison of Celestia. I change the directory name so it has the version of Celestia at the end: e.g. Celestia130

After it has created the directories and copied the program files, the installation script asks you to chose a few more options. Be sure to select "desktop icon", "associate URLs" and "associate .CEL scripts." (I might have the names slightly wrong. This is from memory.)

Note that whenever you run a Celestia installation program, it will change the icon, URL and CEL associations to point to the location of the new program. If it's in a different folder, you can still run the old program by going to its folder and clicking directly on its icon. You also can use the right-mouse-button to drag a shortcut of the old icon to your desktop if you want.

Contents

0:  Introduction.
1: General Overview.
2: A Simple Addon.
3: A Simple Nebula Addon.
4: Installing a Complex Nebula Addon.
5: Installing an Addon of Stars and Planets.
6: Common Addon Problems.
6: Installing Celestia.


Appendices.


A.1: Signature.
A.2: Admonishment.
A.3: Disclaimer.

• Addon Intro in separate pages (for use with Babelfish or other translators)
• Selden's List of Resources for Celestia

A.1: Signature.

This Web page is maintained by Selden Ball at Wilson Lab.

A.2: Admonishment.

Please send any questions, comments or corrections to seb@lepp.cornell.edu
Alternatively, you can post a message (anonymously or otherwise) on Celestia's Web Forum or use its Private Message page.

If you don't tell me that something's missing, unclear or wrong, I can't improve it.

A.3: Disclaimer.

The author disclaims all liability and endorsement.
Copyrights may apply.
For details, please read the full text of his disclaimer.