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, although 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 sky, earth and planet data, although for 3D you'll have to use 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 timeline is also available, so you can see what the constellations looked like as far back as 2,000 years ago. There's also a virtual observatory cone search and registry look-up, and SIMBAD search. The Web version of WordWide Telescope is limited to a geocentric perspective, although Microsoft says it has plans to include multiple points of view in future feature upgrades. You can find the Telescope here.