‘Stellarium’ is one of the best, real-time, 3D, night sky simulation software available, period :). It’s completely free, open-source, runs of GNU/Linux, Windows, Mac OS X & Android.
It comes with star catalogs consisting 600,000 stars (more can be added, manually), big nebulae collection, constellations, 3D rendering (360°) with awesome zooming, search, change location (including into other planets & moons!), a cool telescope simulator (with the ability to tweak magnification settings), sun rise/set simulation, built-in plugins that add more feature & a lot more.
‘Stellarium’ also gets updated frequently & the recently introduced (April 21) version 0.12.1 brigs few major changes, especially concerning the astronomical catalogs. The existing star catalog is updated with ‘Hipparcos’ & ‘Tycho-2’, and also introduces the Caldwell catalog for nebulae too.
The main window has also received minor updates, such as a new Oculars tool-box that sits on the top right corner as well.
According to the release notes page, now it updates textures of Galaxies & nebulae, and over 30 bugs have been fixed in this release as well. I have it installed in Windows 8 too (v 0.12.0) and both zooming & loading times of the application itself is pretty fast under Ubuntu 13.04.
sudo apt-add-repository ppa:stellarium/stellarium-releases
sudo apt-get update
sudo apt-get install stellarium
That’s it. To get more information (& packages for other OS platforms), please visit this page.