Stellarium Astronomy Software

How utterly fab is this? Stellarium Astronomy Software is a free GPL software package that uses OpenGL graphics to render the sky as-it-is-now, and you can zoom in and fast forward through time to see the day/night sky changing. Turn off the atmosphere and you can see what the sun would look like without it.

Zoom in on galaxy M37 and spot the alien civilisation.

Fast-forward to the end of 2007 and you can see the bit where a comet hits us and the world ends.

Superb. Available for sad-sack Linux users and something called Windows (not sure if that's spelt right) too.