For this article, I want to look at the largest thing possible, the wholeuniverse. At least, that's the claim made by Celestia, the softwarepackage I'm introducing here. In all seriousness though,Celestia is a very well done astronomical simulator, similar to othersoftware packages like Stellarium. Celestia is completely open source and islicensed under the GPL.
If Celestia isn't available via thepackage management system for your favorite distribution, you alwayscan get the latest stable version from the Celestia'swebsite asan installable binary package. If you really need the absolute latestversion, you can grab it from the GitHub repository. Binaries also areavailable for Windows and Mac OS X, in case you need to travel onthe dark side of computing.
Once you have installed Celestia, starting it provides a viewof the Earth from space.
Figure 1. Celestia begins your exploration of space with a 3D view of Earth.
You're first placed on a track thatfollows the Earth through space. This is necessary, because Celestiais actually a real-time simulation. If you were in a fixed location inspace, any object you were looking at quickly would leave your fieldof view. You can pause the simulation by pressing the spacebar. Onceyou are following an object, you can rotate your view by clicking theleft mouse button and dragging left/right or up/down.
If you're more interested in observing a centered object, youcan click the right mouse button, and then dragging will move you around theobject instead, allowing you to see the object's details. You canzoom in or out by using the mouse wheel. All of these navigation actionsalso have keyboard shortcuts, for those who prefer that to using a mouse.
But, how do you select which object you are centered on? The easiestoption is to click the Navigation→Solar System Browser menu item topop up a selection window.
Figure 2. You can use the solar system browser to select objects to centeron within the solar system.
From here, you can choose fromplanets, moons, asteroids and other solar system objects availableby default within Celestia (I'll explain how to add even more itemsshortly).
If you're looking at items beyond the solar system, you canclick the Navigation→Star Browser menu item to open a newwindow.
Figure 3. You can view objects beyond the solar system by bringing up thestar browser window.
From here, you can select from a large numberof stars that are available in the standard library. If you want togo to a specific object or a specific location, click theNavigation→Goto Object menu item to open an input dialog whereyou can enter the details of where you want to go.
Figure 4. You can go to specific locations within the universe.
Until now, all of the objects that are available for viewing come withthe standard installation of Celestia. However, Celestia also includes theability to add extra items to the catalog. You can add object files forthese additional objects in the extras sub-directory where Celestiais installed.
Several available objects are hosted at theCelestia Motherlode website. These are zip files, containing everythingyou need if you want to include that object in your installation ofCelestia. You also can create your own extra objects and upload them to theCelestia Motherlode site in order to share them with other users.
You mostly interact with Celestia via text files. You candefine how it behaves at start up by editing the start.cel andcelestia.cfg files. These files are well commented, so you should be able totune the way Celestia behaves relatively easily.
This interaction extendsto being able to script Celestia, which is handy if you want touse it to create guided tours of celestial objects to showother people. These scripts are text files, with the filename endingin .celx. There's a complete scripting language that allows you tocontrol most aspects of Celestia.
Once you have a certain view prepared, there are a few ways to share it withothers. If you click File→Capture Image, a pop-upwindow appears where you can save the currently rendered view aseither a JPEG or PNG image file. Clicking File→Capture Movie opensa window where you can record a video file of what's occurring onthe screen right then. You also can select the compression scheme to useor leave it as raw video.
Figure 5. You can choose the video compression scheme to use when yourecord a video from Celestia.
This is handy if you want toshare a tour of the universe with someone who may not have Celestiainstalled. However, instead of sharing images or videos, you also can sharesomething called a Celestia URL (or Cel: URL). This URL includes thedetails of the rendered view, but when you doshare it, the other person needs to have Celestia installed. Onething to be aware of is that there are some incompatibilitiesbetween versions of Celestia, so you may need to coordinate with theother person if you run into any issues.
Celestia should make a great addition to your astronomy toolkit.Its ability to script views is especiallyuseful if you want to share something with students. See also theCelestiaWikibook for more information.
Recent Articles
