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From starlight to insight

Tonight, as the sun sinks below the horizon, the world’s most powerful digital camera will once again turn its gleaming eye skyward. For hundreds of nights over the next four years, the images from this camera will be transmitted directly to NCSA as a team of astronomers and physicists from around the globe try to answer some of the most fundamental questions about our universe.

The Dark Energy Camera (DECam) is the most powerful survey instrument of its kind, able to see light from more than 100,000 galaxies up to 8 billion light-years away in each snapshot. The camera began transmitting images on Aug. 31, 2013, and is the main tool of the Dark Energy Survey (DES). It is the result of years of planning, building, and testing by more than 200 collaborators at 25 institutions in six countries.

Using DECam, DES scientists will systematically map one quarter of the southern sky (5,000 square degrees) in unprecedented detail. The goal of this survey is to understand why the expansion of the universe is accelerating instead of slowing down due to gravity. The force behind that acceleration has been named “Dark Energy” but the scientists will not be able to see dark energy directly. Instead, by studying the distribution, shapes, colors, and motion of galaxies, the details of the expansion of the universe and the growth of large-scale structure over time will give scientists clues to the physical nature of Dark Energy.

The main tool of the survey is the DECam, a 570-megapixel digital camera built at Fermilab in Batavia, Ill., and mounted on the 4-meter Victor M. Blanco telescope at the National Science Foundation’s Cerro Tololo Inter-American Observatory in the Atacama Desert in Northern Chile. The camera includes five precisely shaped lenses, the largest nearly a yard across, that together provide sharp images over its entire field of view.

During a normal night of observations, DES produces about 1 terabyte of raw data, including science and calibration images, which are transported automatically from CTIO in Chile to NCSA within minutes of being observed. These images are usually processed within the next 24 hours. Over five years, the survey will obtain color images of 300 million galaxies and 100,000 galaxy clusters and will discover 4,000 new supernovae, many of which were formed when the universe was half its current size.

The DES data management (DESDM) system—developed by collaborating DES institutions and led by NCSA—is in charge of the processing, calibration, and archiving of these images and the resulting catalogs of galaxies and their physical properties. Using NCSA’s iForge supercomputer, the DESDM team at NCSA processes the raw data generated by the DECam into these science-ready data products that are stored by NCSA’s Storage Enabling Technology Group. The DESDM team is led by Don Petravick and includes Ricardo Covarrubias, Gregory Daues, Margaret Gelman, Michelle Gower, Robert Gruendl, Michael Johnson, Felipe Menanteau, and Todd Tomashek.

Initially, DESDM will provide the science-ready products to the DES collaborators. Then, after a proprietary period, they will be available to the entire astronomical community. DESDM will also host two public data releases, one about midway through the survey and a final release.

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