Science and Exploration

Sloan Digital Sky Survey Expands Its Reach

By Keith Cowing
July 16, 2014
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Sloan Digital Sky Survey Expands Its Reach
Sloan Digital Sky Survey
Sloan Digital Sky Survey

Building on 14 years of extraordinary discoveries, the Sloan Digital Sky Survey (SDSS) has launched a major program of three new surveys, adding novel capabilities to expand its census of the Universe into regions it had been unable to explore before.
This new phase of SDSS will:

-Explore the compositions and motions of stars across the entire Milky Way in unprecedented detail, using a telescope in Chile along with the existing Sloan Foundation Telescope.

-Make detailed maps of the internal structure of thousands of nearby galaxies to determine how they have grown and changed over billions of years, using a novel optical fiber bundle technology that can take spectra of each different part of a galaxy at once.

-Measure the expansion of the Universe during a poorly understood five-billion-year period of the Universe’s history when Dark Energy started to drive its expansion, using a new set of galaxies and quasars.

The new survey is a collaboration of more than 200 astronomers at more than 40 institutions on four continents and incorporates telescopes in both the Northern and Southern Hemispheres. With these two telescopes, the SDSS will be able to see the entire sky for the first time.

“Over the last fourteen years, many people have used SDSS data to make numerous discoveries that have revolutionized astronomy,” said Michael Blanton of New York University, the director of the new survey. “We have mapped the large-scale structure of the Universe, traced out previously unknown structures in the Milky Way, and made unanticipated discoveries from asteroids in our own Solar System to the most distant quasars.”

This new phase of the SDSS will provide a vast new database of observations that will significantly expand our understanding of the nature of the Universe at all scales, from our own galaxy to the distant universe. In our galaxy, the new SDSS will see hundreds of thousands of individual stars, including stars that were born at the birth of the Milky Way and stars born in the past few million years, just yesterday in cosmic terms. Measuring the compositions, positions, and motions of individual stars will reveal how the Galaxy evolved from the distant past to today.

“The SDSS has observed more than half a million Milky Way stars over the past fourteen years, which I call a good start,” said Jennifer Johnson of The Ohio State University, the Scientific Spokesperson of the new SDSS. “However, from the Northern Hemisphere, the Earth blocks our view of a quarter of the Milky Way, and mostly obscures our view of the galactic center. So there are literally entire regions of the Galaxy that the SDSS has yet to see.”

This new phase will complete the picture. In addition to the Sloan Foundation 2.5-meter Telescope in New Mexico, SDSS will use the 2.5-meter Irenee du Pont Telescope at Las Campanas Observatory, high in the Chilean Andes and home to the clearest skies on the planet. In addition to completing our full study of the Milky Way, the du Pont telescope will also observe stars in the nearby Magellanic Clouds, giving astronomers a better understanding of the Milky Way’s immediate environs.

To take advantage of the scientific opportunities that the new SDSS offers, a number of Chilean universities have joined together for the first time to form a “Chilean Participation Group,” which will be a member of the SDSS collaboration. “We are delighted to become a part of the new Sloan Digital Sky Survey, and we look forward to being active participants in this unique project to explore our Universe,” said Doug Geisler, a professor of astronomy at Universidad de Concepcion and chairperson of the Chilean Participation Group Executive Committee.

But the Milky Way is far from the only galaxy that the new SDSS will examine. The new survey will employ innovative new technology to make detailed maps of thousands of nearby galaxies. Unlike nearly all previous astronomy surveys, which looked only at the centers of other galaxies, the new SDSS will measure light from all of the different parts of a galaxy. These better maps are made possible through a new technique of bundling sets of fiber-optic cables into tightly packed arrays. These fiber arrays collect light from across the entire extent of a galaxy, enabling detailed spectral measurements of more than 10,000 nearby galaxies at twenty times the rate of previous surveys, which did one galaxy at a time.

“Our goal is to understand the ‘life cycle’ of present-day galaxies from imprinted clues of their birth and assembly, through their ongoing growth via star formation and merging, to their eventual fadeout after star formation ends,” said Matt Bershady, the Project Scientist of the new SDSS.

And the new SDSS will continue to improve our understanding of the Universe as a whole. It will precisely measure the expansion history of the Universe through 80% of cosmic history, back to when the Universe was less than three billion years old. These new detailed measurements will help to improve constraints on the nature of dark energy, the most mysterious experimental result in modern physics.

The new cosmology measurements will include the largest and most complete three-dimensional map of quasars to date, which will allow for precise measurements of the history of the Universe’s expansion in ways never before possible. Other programs within the new SDSS will follow up on galaxies seen by prior x-ray surveys, and will conduct the first systematic spectral study of variable objects, yielding a critical resource astronomers can use to identify the nature of many types of time-varying light sources discovered in previous surveys.

With new twists on its powerful instruments, a new outpost in the southern hemisphere, and the continuing generous support of the Alfred P. Sloan Foundation, the SDSS will remain one of the world’s most productive astronomical facilities. Science results from the SDSS will continue to reshape our view of the fundamental constituents of the cosmos, the universe of galaxies, and our home in the Milky Way.


Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation and the Participating Institutions. SDSS-IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is .

SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofisica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut fur Astrophysik Potsdam (AIP), Max-Planck-Institut fur Astrophysik (MPA Garching), Max-Planck-Institut fur Extraterrestrische Physik (MPE), Max-Planck-Institut fur Astronomie (MPIA Heidelberg), National Astronomical Observatory of China, New Mexico State University, New York University, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autonoma de Mexico, University of Arizona, University of Colorado Boulder, University of Portsmouth, University of Utah, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.

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