University of Pittsburgh
July 31, 2013

Exploring the Hidden Milky Way

Sloan Digital Sky Survey III releases public dataset featuring 60,000 stars

PITTSBURGH—Today, astronomers with the Sloan Digital Sky Survey III (SDSS-III) announce the release of “Data Release 10,” a new online public dataset featuring 60,000 stars that are helping to tell the story of how our Milky Way galaxy formed.

Data Release 10 is a new set of high-resolution stellar spectra—measurements of the amount of light given off by a star at each wavelength—using infrared light that is invisible to human eyes but able to penetrate the veil of dust that obscures the center of the galaxy. These new spectra are the first data released by the SDSS-III’s Apache Point Observatory Galactic Evolution Experiment (APOGEE), an effort to create aA photo of four SDSS-III scientists working on the APOGEE spectrograph.  Left to right: Garrett Ebelke (Apache Point Observatory), Gail Zasowski (The Ohio State University), Steven Majewski (University of Virginia) and John Wilson (University of Virginia). Majewski is actually standing across the room; he appears here as a reflection in a mirror that was being installed in the spectrograph.  Image credit: Dan Long (Apache Point Observatory) comprehensive census of our Milky Way galaxy.

“This is our tenth data release since 2001, and we’re not slowing down yet,” said SDSS-III Spokesperson Michael Wood-Vasey, assistant professor of physics and astronomy at the University of Pittsburgh. “Public access to data has always been a key goal of our project. We are proud to continue that tradition today.” 

To accomplish its goal of observing 100,000 stars in just three years, the APOGEE instrument observed up to 300 different stars at a time using fiber-optic cables plugged into a large aluminum plate with holes drilled to line up with each star. Light passes through each fiber into the APOGEE spectrograph, where a prism-like grating distributes the light by wavelength. The grating is the first and largest of its kind deployed in an astronomy instrument.

The data provide a rich context for investigating questions about the stars themselves. Because APOGEE observes each target star several times, it can identify changes in each star’s spectrum over time. This feature has enabled the APOGEE team to discover unusual types of rapidly variable stars, to pinpoint how many stars are actually binary stars with unseen companions, and even to detect the subtle stellar motions caused by orbiting exoplanets.

Data Release 10 also publishes another 685,000 spectra from the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). These new spectra come from galaxies and quasars as seen when our universe was much younger, just as the mysterious force of “dark energy” was beginning to influence the universe's expansion. The new BOSS spectra, and the additional spectra that the SDSS-III will continue to obtain in the final years of the survey, will help scientists in their quest to understand what dark energy might be.

The new data have the potential not only to revolutionize our understanding of the Milky Way, but also to make a major impact on public understanding of science. Like all SDSS data, all data from Data Release 10 are available online.

“This is the most comprehensive collection of infrared stellar spectra ever made," said Steven Majewski of the University of Virginia, the lead scientist for the APOGEE project. “These 60,000 stars are selected from all parts of our galaxy, including the nearly-empty outskirts to the dust-enshrouded center. Our spectra are allowing us to peel back the curtain on the hidden Milky Way.”

Visit to learn more about the Sloan Digital Sky Survey III. 

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