Overview
Have you ever wondered what the astronauts really see when they look out their windows? How 'bout what it's like to fly thru Saturn's rings? Or even what the constellations look like from 50 lightyears away?

With Celestia, you can find out.

Available for free download at www.shatters.net/celestia, Celestia is described as a "real-time space simulation that lets you experience our universe in three dimensions. Unlike most planetarium software, Celestia doesn't confine you to the surface of the Earth. You can travel throughout the solar system, to any of over 100,000 stars, or even beyond the galaxy. All travel in Celestia is seamless; the exponential zoom feature lets you explore space across a huge range of scales, from galaxy clusters down to spacecraft only a few meters across. A 'point-and-go' interface makes it simple to navigate through the universe to the object you want to visit."

Celestia was written by a Seattle programmer who wanted to create an application that would enable the user to view the Solar System and beyond. He wanted the user to do so at any moment in time, and from any vantage point they chose. To date, over 2 million copies of Celestia have been downloaded. Users range from graphic artists to astrophysicists, from teachers to astronomers.

Installation
Celestia is available for OS X, Windows, and Linux. I downloaded the 12-Meg OS X version (1.3.1). I could not find a reference to minimum Mac requirements, but I was able to load and run Celestia on a 350-Mhz iMac G3, as well as on my G4, I'd hazard to guess that it can run on any system running Panther. A graphics card with at least 64 Megs of memory for running higher-resolutions textures is also recommended. My system only has 32 Megs for graphics, and I found the rendering to be outstanding. Setup of Celestia is extremely easy. The file downloads as a disk image (.dmg), and you just drag 'n drop the folder where you want it.

In Use
The controls for Celestia are not intuitively obvious. I highly recommend downloading the 2-megabyte user's manual (in MS Word) that is also available. It became extremely useful while experimenting with the software. The manual does have a keyboard-command list at the end. However, the manual was clearly written for Windows users. There are several left-click/right-click commands. Celestia does have quite a lot of pull-down menus (and a functioning Help menu). I also found that while Celestia supports a fairly sizeable list of joysticks, my iStick is not on the list. I would have liked to use it to navigate. On the plus side, once I did master the key commands, it was very easy to move my "ship". I especially liked the "point and go" feature. I could select an object in the sky by clicking on it, and hit the G key to fly to it. 

Immediately upon startup, I was looking at a wonderfully rendered Earth. I increased the resolution immediately (keyboard [R]), added cloud and atmosphere textures (keyboard [I] & [CTRL-A]), and was looking at a space-shuttle view of the earth. Included with the download is a short demo script that is fairly reminiscent of the "Powers of 10" short (keyboard [D]). It takes you on a tour of the Solar System, and beyond. I highly recommend it. Other Celestia Developers (the shatters website above as links to them) have created their own scripts, including tours of the Earth, the Moon, the Milky Way, the moons of Jupiter, and many more.

The rendering is outstanding. There is functionality to increase texture resolution, add clouds, atmospheres, cities (city lights show up on the night-side), and more.

Low-res planet Earth

High-res planet Earth

There are several Easter Eggs in Celestia, such as Apollo 11 in orbit around the moon. Another has the ISS in orbit around the earth. Keyboard commands [enter][ISS][enter][g] automatically flew me to the space station. Though the model that is standard with the program is a good rendering, there are models available on the web that are textured at higher resolutions. Scripts also exist that enable you to watch the construction of the space station (time can be sped up, down or reversed with keyboard clicks).

I spent several days zipping around the galaxy, downloading script upon script. I traveled into the distant past and watched the Pangea super-continent split to form the 7 continents of present. I traveled into the future to see huge orbiting mirrors melt Mars' polar ice-caps. There are even authors that have created literally hundreds of planets to visit while exploring the galaxy. It was way cool to watch the Earth-rise from orbit above the moon.

View from the Moon of the Earth Rising

Summary
Celestia is a fun tool to explore and view our galaxy. If you have an interest in astronomy, it can be a great reference tool. If you have kids, having them visit the planets is a great learning tool. The ability to script travel through space gives users great potential for developing instruction material, games, etc.. I enjoyed simply orbiting the earth and watching it revolve around me.  The graphics are out of this world (figuratively and literally). Celestia does not allow you to define the keyboard controls to user preferences, and although it supports some joysticks, and does not support the iStick. It includes an extensive user's manual, albeit it is Windows-centric. The bottom line is that Celestia is fun, and it is free. If you wonder what the view home from Voyager One looks like, or if you just want to get out and explore the galaxy without leaving your home, then Celestia is a must-have. I'm looking forward to downloading and playing some of the games that are being written using the Celestia engine.

Pros

• Simple installation
• Fantastic rendering of planets
• Point-and-click navigation
• Constellation on/off feature (look at Orion from 1000 light-years to galactic north)        
• User's manual is extensive

Cons

• Keyboard commands not intuitively obvious
• No Joystick control for the iStick
• The User's manual is written for Windows users

Overall Rating

4 out of 5 Mice