Celestia - the heavens on your laptop

I'm moved to write about a particularly impressive piece of open sourcei and free software that I've just come across: it's called Celestia, and it is a fully immersive 3D model of the known universe for your computer. Unlike many planetarium programs, it is not limited to viewing the night sky from Earth. You can travel anywhere in the known universe as if in a space ship and view anything from any angle or any point. You can even travel back and forwards in time. All the phenomena are based on real data from astronomical calculations and observations, and the level of detail in some circumstances is startling.

I wanted to blogi about this because Celestia is a free program, that is not even very large to download, that works across three different operating systems (Windows, Mac and Linuxi) and has attracted collaboration from a wide number of people (4,600 according to the Users Guide (which you must have if you wish to understand how the controls work, and which can be downloaded from here)).

To date, apparently nearly 3 million people have downloaded the program.
The Celestia community has contributed to many add-ons that enhance the experience and can be downloaded from the site. So, for example, although the program comes with a basici set of 100,000 stars you can download an add-on for over 2 million extra stars, each and every single one of them scientifically accurate in its naming, position and type. To me, this is the type of knowledge that is kept in astronomical observatories or stellar physics labs, not on a home computer: so the very power and scope of Celestia is exciting to me.
It even knocks into a cocked hat the scope of the London Planetarium I visited as a child.

The elements in Celestia are realistic and useful too: compare the image of the Ant Nebula from the add-on 3D model with an actual image from the Hubble telescope, and look at the paths of planetary orbits that can be switched on or off, seen looking from the Moon towards Earth.

The add-ons expand to hobbyists who have - for example - recreated fictional objects from Star Trek, such as the Enterprise in the charged plasma field of "Deep Space Nine"'s fictional Denorios Belt. Other more esoteric and classical contributions include a complete representation of Johann Hevelius's 1690 work Uranographia: a fanciful representation of the star signs as animals and mythical characters, warring, biting and gliding their way across the heavens.

The other good thing that I really want to mention about Celestia is that it's not buggy. It doesn't tend to crash, and it does do what it promises to do, and more. There are multiple and exciting options for lighting, texture and labeling. Even the documentation (unusual - in my opinion - for many "enthusiast" projects) is accessible and clear (although I still believe that page 27 should be the first page, but at least the information is all there somewhere, even though some geeky presentational flaws remain).

So, in short, I highly recommend Celestia: I grew up with a couple of really good books about astronomy. Now, my son could fly his way around a 3D realistic universe. That's progress, and it's collaborative, non-commercial, free to use, and expanding all the time.