# Celestia/Tutorials

Celestia has a wide variety of object types, including everything as tiny as satellites to massive galaxies millions of light-years across. Practically any and all of them can be added to Celestia. However, it takes some knowledge to do this accurately. Depending on the object, you may need some knowledge of Celestia and SSC/STC/DSC file, astronomy, modeling, programming, and/or general computer knowledge.
Therefore, the following pages have been made to help people create scientifically accurate add-ons.

## Table of contents

These tutorials are split into three sections: Solar System objects, extrasolar objects, and deep-sky objects. To use a tutorial, look at that page, and if they exist, any pre-requisite tutorials.
1. Creating Solar System Objects
* Asteroids (basic): Adding simple asteroids to Celestia. Once you have read this tutorial, you can progress to the next four:
* Comets: Adding comets to Celestia.
* Asteroids (advanced): More advanced aspects of asteroid-making in Celestia. This page includes how to prepare models of asteroids, how to calculate the approximate color of an asteroid, how to orientate the asteroid so it rotates correctly, and how to add asteroid satellites.
* Moons: Adding natural satellites around objects in Celestia.
* Near-Earth Asteroids: Making asteroids whose orbits get perturbed in Celestia.
2. Creating Extrasolar Objects
* Stars: Adding stars to Celestia. Once you have read this tutorial, you can progress to the next two:
* Star Systems: Adding binary stars and multiple star systems to Celestia.
* Exoplanets: Adding exoplanets to Celestia.
3. Creating Deep-Sky Objects
* Galaxies: Adding galaxies to Celestia.
* Globulars: Adding globular clusters to Celestia.
However, before you start making add-ons to Celestia, there are a few things that are useful/essential to know, detailed below.

## What are add-ons?

Add-ons are files that you can install that modify Celestia in some way. Often they will include new objects, or they may include better or higher-resolution textures for existing objects.
Add-on files typically contain the following:
* An SSC, STC, and/or DSC File. These are simply plain text files where the .txt suffix has been renamed to .ssc, .stc, or .dsc. In them, they contain instructions that Celestia uses to draw objects.
These can be edited by any plain text editor, such as Notepad++ or TextEdit. Be aware, however, that some text editors such as TextEdit will naturally turn use "smart quotes". These are a different symbol than the typical quotation marks used in most code, and computer files made with them tend to not work. Fortunately, these can be usually be changed in the preference menus.
They may also contain:
* Models. These tell Celestia the shape of the object.
* Textures. These are images that Celestia uses to actually render the objects.
Add-ons will typically contain a text file called "README.txt". In it, they will often say to "move this file to the extras directory". What does this mean? Well, to show all of the stars, planets, and other astronomical objects, Celestia reads files from a folder in your computer, called "Celestia" if you're on a Windows or Linux system or "CelestiaResources" if you're on a Mac.

## How do I install add-ons?

On Windows or Linux, open the "Celestia" directory and you'll see the "extras" directory right there. If you're on a Mac, right-click on the Celestia app and click on "Show Package Contents". Then, go to "Contents" → "Resources" → "CelestiaResources". All the stuff in this folder (such as the "data" folder, "models" folder, "celestia.cfg", etc.) is used by Celestia to render objects. There is also a folder in there called "extras". When instructions tell you to move a file to the "extras directory", they are talking about this file.
So to recap: to install an add-on, simply move it to the "extras" folder.

## External links

A good place to download add-ons is the Celestia Motherlode. Here, there are literally gigabytes of add-ons, including everything from ultra-high-resolution textures of the Earth to distant galaxies and nebulae.
The Celestia Motherlode also has a more detailed guide on installing add-ons here: Add-on Installation.