SDSS delivers a new look at the sky

Astronomers are crunching enormous amounts of data and amassing more all the time. It’s almost enough to make one think that there’s more data in the universe than the universe can hold, but that would be something of a paradox.

Another 100-terabyte chunk of data was delivered to the astronomical community Jan. 6. The Sloan Digital Sky Survey (SDSS) made the final release of the third epoch of its survey (SDSS-III) in Seattle at the 225th meeting of the American Astronomical Society. Data Release 12 (DR12) contains measurements of the properties of nearly half a billion stars and galaxies, making it one of the largest and richest databases in the history of astronomy. SDSS-III spent six years collecting that data using the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory in New Mexico.

A still photo from an animated flythrough of the universe using 

SDSS data. This image shows our Milky Way Galaxy. The galaxy 

shape is an artist’s conception, and each of the small white dots 

is one of the hundreds of thousands of stars as seen by the SDSS. 

Image credit: Dana Berry / SkyWorks Digital, Inc. and Jonathan 

Bird (Vanderbilt University).

“The most astonishing feature of the SDSS is the breadth of ground-breaking research it enables,” said Daniel Eisenstein of the Harvard-Smithsonian Center for Astrophysics and director of SDSS-III. “We’ve searched nearby stars for planets, probed the history of our Milky Way, and measured nine billion years of our universe’s accelerated expansion.”

DR12 includes data from several different surveys.

APOGEE (the Apache Point Observatory Galactic Evolution Experiment) looked in near-infrared wavelengths to see through obscuring dust clouds and mapped the distribution of 15 separate chemical elements in more than 100,000 stars, probing all regions of the Milky Way.

“That’s a huge amount of information,” said Steve Majewski of the University of Virginia, APOGEE’s principal investigator, “and each element reveals a different subplot in this galactic screenplay. Sometimes the interactions between the characters are quite surprising!”

MARVELS (the Multi-Object APO Radial Velocity Exoplanet Large-Area Survey) made repeated measurements of 3,000 stars to detect the back-and-forth motions that could reveal unseen orbiting planets.

“MARVELS is the first large-scale survey to measure these tiny motions for dozens of stars simultaneously,” said principal investigator Jian Ge of the University of Florida, “which means we can probe and characterize the full population of giant planets in ways that weren’t possible before.”


BOSS (the Baryon Oscillation Spectroscopic Survey) maps the fossil imprints of sound waves that filled the universe during the first half-million years after the Big Bang. The BOSS team is using those imprints to trace the expansion of the universe across nine billion years of cosmic history, with unprecedented precision.

SEGUE (the Sloan Extension for Galactic Understanding and Exploration) measured visible-light spectra of a quarter-million Milky Way stars.

“Data release 12 is the largest SDSS data release so far, it contains data that make more precise measurements than before, new kinds of data in new wavelength ranges for the survey facility, and new techniques for making those measurements,” said Connie Rockosi of U.C. Santa Cruz, the lead scientist for the Sloan telescope. Rockosi added that more science is certain to come now that all of that data has been released to the public.

And there’s more data to come. SDSS-III may be finished, but SDSS-IV began began a six-year mission last July to study cosmology, galaxies, and the Milky Way.