Google's desktop terrestrial mapping software now features extra-terrestrial data, detailing what you might see when you look up.

"Today, I'm excited to announce we are launching Sky in Google Earth," said Lior Ron, product manager for Google Earth, in a blog post on Wednesday. "You can now explore the universe from the comfort of your chair. Zoom in to distant galaxies hundreds of millions of light years away, explore the constellations, see the planets in motion, witness a supernova explosion; it's like having a giant, virtual telescope at your command -- your own personal planetarium!"

A Sky button in the latest version of Google Earth, currently available for download, toggles the view from planetary to celestial. The new data set includes 100 million stars and 200 million galaxies. Google has prepared a video primer for novice virtual astronomers.

Google has updated the Google Earth Gallery with several astronomical images that detail the motion of our solar system, exoplanets, and Hubble Space Telescope pictures. The gallery includes links to KMZ files that open in Google Earth.

Sky in Google Earth includes several data layers that highlight specific celestial bodies including the moon, the planets, and the life of a star.

While Google Local ads can be seen on Google Maps and on Google Earth, the sky remains ad-free, at least for the time being.

In September 2005, Google and NASA announced that they'd signed a memorandum of understanding to cooperate in the development of large-scale data management and distributed computing technologies. At the time, CEO Eric Schmidt cited making images from the Apollo space mission more accessible to Internet users as one possible benefit of the arrangement.

At Microsoft TechFest in March, Microsoft demonstrated a project called World-Wide Telescope, a software-based telescope emulator for PCs.

Sky in Google Earth is available in 13 languages.