You're the master of time, so you can make it run slower, faster or even stop it; you're the master of space, so you can change the position to anywhere you want; you can also control the events by running or recording scripts that simulate eclipses or other astronomical events.
It's very refreshing to use it as a virtual telescope that teaches you to look at the sky and to understand more from its mystery.
Related:
Celestia, space simulator
Google Earth, as seen by a Googler