Last year, Microsoft introduced its answer to Google Earth's Sky mode, Stellarium, and other celestial mapping programs with WorldWide Telescope, and it's now making it available via any browser that's been bolstered by Silverlight. The basic features of the downloadable program have been ported to the Web, though some of the higher-end renderings didn't make the cut.
As in the desktop version, users can whip around the galaxy using their mouse's scroll wheel to zoom in and out, and hold down the left mouse button to drag the sky from one position to another.
Users will continue to get access to hundreds of terabytes of data on the sky, Earth, and other planets, though for 3D viewing, you'll have to hit up the full program. Thumbnail previews show off relevant and nearby astronomical bodies of interest, and one of the strongest features from the desktop--the tours made by both astronomers and amateurs--are also available here.
The time line is also available, so that you can see what the constellations looked like as far back as 2,000 years ago, and there's a virtual observatory cone search and registry look-up, as well as SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data) search.
The Web version of WordWide Telescope is limited to a geocentric perspective, though Microsoft says it has plans to include multiple points-of-view in future feature upgrades.