Google has announced a nifty extension to its Google Earth which allows users to scan the night sky in search of constellations, planets, and other extraterrestrial wonders - Google Sky:

The add-on is available on the latest version of Google Earth, and hitting the "Switch between Sky and Earth" button on the top toolbar immediately offers an upward view with seven optional layers: Constellations; Backyard astronomy (info on objects visible to the eye and via small telescopes); Hubble Showcase (129 high-res Hubble snaps); The Moon (two months of lunar positions and phases); User's Guide to Galaxies (virtual galaxy tours); Life of a star (a star's life cycle explained); and Planets (positions of seven planets two months ahead). Here's some info on Mars: