SEATTLE – The Sloan Digital Sky Survey collaboration released the largest-ever digital color image of the sky today.

The new image consists of 1.2 trillion pixels and covers a third of the night sky, capturing half a billion individual stars and galaxies. Every yellow dot in the image (above) is a galaxy, and zooming in on each dot reveals a galaxy's detailed structure and individual star-forming regions.

"We have that sort of detail for this entire area," said astronomer Michael Blanton of New York University at a press conference here at the American Astronomical Society meeting. "It's not just really big, it's also really useful."

The survey has been taking multicolored images of the sky from a single 2.5 meter telescope in New Mexico since 1998 and releasing the photos to the public almost immediately. Its sharp shots of millions of galaxies laid the foundations for citizen science projects such as Galaxy Zoo, Google Sky and World Wide Telescope.

The first two iterations of the survey, called SDSS-I and SDSS-II, covered part of the sky called the northern galactic cap (bottom right in the image above). SDSS-III ran from July 2008 to December 2009 and completed the survey by covering the entire southern galactic cap (bottom left).

"What makes this a really special moment is that this release really completes the mission of the SDSS camera that's been going on for 11 years," Blanton said. The camera that took images in the part of the electromagnetic spectrum visible to human eyes stopped running in December 2009.

But SDSS will continue to take data in other wavelengths for several years. The new publicly available data dump (which is about 30 terabytes in size) includes spectra of millions of galaxies up to 7 billion light-years away, which will help astronomers understand the history of the universe and the effects of dark energy on cosmic structure. A survey called BOSS, which began in 2009 and will run until 2014, will convert the new 2-D image into the largest 3-D map of the distant universe.

SDSS-III also collected spectra from millions of stars as part of a survey called SEGUE-2, which will help astronomers identify streams of stars that the Milky Way stole from smaller satellite galaxies. Astronomers believe large galaxies formed by cannibalizing smaller galaxies that got too close. The remains of these hapless galaxies show up as streams of stars that still move as a flock through the Milky Way.

"For the parts of the sky where we have SEGUE-2 data, we can make a more complete census of these streams, and get a better idea of how our galaxy grew by seeing the remnants of galaxies that were torn apart by our own galaxy," said astronomer Connie Rockosi of the University of California, Santa Cruz.

"This is going to be a really unique reference for the next decade or longer," Blanton said. "It’s a true legacy data set."

Image: M. Blanton and the SDSS-III

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