Getting hold of a copy of Google Earth for OS X, for browsing planet Earth, is one thing; but getting hold of an app that lets you browse the night sky is quite another.
Stellarium is the inverse of Google Earth. Instead of floating above the ground looking down, Stellarium is for looking up.
It’s incredibly simple to use. You tell it where you are in the world (either by clicking on a map, or just entering your latitude/longitude co-ordinates), and you tell it what the time is (which it can just get from your system settings anyway), and fire it up.
It shows you, in full-screen glory, the sky. Not just a picture of the sky, but everything in it; the planets, nebulae, constellations and galaxies that we can view from Earth.
And like Google Earth, the view is incredibly customizable. A bunch of useful extra data and cool visual effects can be toggled on and off with ease. You can either view the sky just as it is from your bedroom window, or you can switch off the ground and the atmosphere, add nebulae and constellation artwork, and browse the sky as if it were an interactive textbook. Written and drawn by da Vinci.
Stellarium is an example of open source development at its very best. This application looks so polished, so professional, that you’d think it had been created by a commercial software house with millions of dollars to spend. Instead, this is the work of volunteers, and is even more impressive as a result.