Penn State participates in largest color image of the sky ever made

January 13, 2011

The largest digital color image of the sky ever made is being released this week by the Sloan Digital Sky Survey-III (SDSS-III). The image has been put together over the past decade from millions of 2.8-megapixel images captured by the telescopes of the SDSS collaboration, creating a color image of more than 1 trillion pixels that is the most comprehensive view of the night sky ever made. This terapixel image, which is freely available to everyone, is so big and detailed that 500,000 high-definition TVs would be needed to view it at its full resolution.

"The quality and the scope of this image are truly breathtaking," said Lawrence Ramsey, Head of Penn State's Department of Astronomy and Astrophysics and a member of the SDSS-III Advisory Council.

The new image is at the heart of new data being released by the SDSS-III collaboration at the 217th American Astronomical Society meeting in Seattle, Washington. This new SDSS-III data release, along with the previous data releases that it builds upon, provides the latest, most precise positions, colors, and shapes for nearly a half-billion astronomical objects, including asteroids, stars, galaxies, and distant quasars.

Donald Schneider, a distinguished professor of astronomy and astrophysics at Penn State, is the SDSS-III Survey Coordinator and is in charge of scheduling the observations of the SDSS-III survey. Penn State is one of three Pennsylvania institutions, along with the University of Pittsburgh and Carnegie Mellon University, that have scientists involved in the large SDSS-III collaboration -- an international team of scientists at participating institutions in the United States, Brazil, the United Kingdom, France, Germany, Spain and Japan.

The image was started in 1998 using what was then the world's largest digital camera -- a 138-megapixel imaging detector mounted on a dedicated 2.5-meter telescope at the Apache Point Observatory in New Mexico. Over the last decade, the Sloan Digital Sky Survey has scanned a third of the whole sky. This imaging camera is now being retired, and will be part of the permanent collection at the Smithsonian in recognition of its contributions to astronomy.

"It has been wonderful to see the science results that have come from this camera," said Connie Rockosi, an astronomer from the University of California Santa Cruz, who started working on the camera in the 1990s as an undergraduate student with Jim Gunn, professor of astronomy at Princeton University and SDSS-I/II project scientist. "It's a bittersweet feeling to see this camera retired, because I've been working with it for nearly 20 years."

This enormous image is forming the basis for new surveys of the universe using the SDSS telescope. These surveys rely on spectra, an astronomical technique that uses instruments to spread the light from a star or galaxy into its component wavelengths. Spectra can be used to find the distances to distant galaxies and to reveal the properties of different types of stars and galaxies -- such as their temperature and chemical composition.

Niel Brandt, distinguished professor of astronomy and astrophysics at Penn State, is the leader of two projects involving the new SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), an SDSS instrument that recently has been upgraded. "I am encouraged by the quality of the initial data from the upgraded BOSS instrument," Brandt said.

"The spectra of the quasars obtained by BOSS will allow us to investigate the physical conditions that exist near supermassive black holes." The SDSS scientists also are using the BOSS instrument to measure the distances to the over one-million galaxies detected in the new terapixel image.

The SDSS-III collaboration also has been studying the properties and motions of hundreds of thousands of stars in the outer parts of our Milky Way Galaxy -- a survey, known as the Sloan Extension for Galactic Understanding and Exploration -- or SEGUE. In conjunction with the release of the new terapixel image, astronomers from SEGUE also are releasing the largest map of the outer Galaxy ever published. The map reveals many streams of stars that originally belonged to other galaxies but have been torn apart by the gravity of the Milky Way.

Suvrath Mahadevan and Jason Wright, assistant professors of astronomy and astrophysics at Penn State, are using the Hobby-Eberly Telescope -- of which Penn State is a principal partner -- to perform detailed studies of the planets that will be identified by two other SDSS-III surveys of our Galaxy through 2014. The first, called MARVELS, will use a new instrument to repeatedly measure spectra for approximately 8500 nearby stars like our own Sun, looking for the tell-tale wobble caused by large Jupiter-like planets orbiting them. MARVELS is predicted to discover around a hundred new giant planets, and to possibly find a similar number of "brown dwarfs" that are intermediate between the most massive planets and the smallest stars. "MARVELS is surveying an unprecedented number of stars for velocity variations, and we expect a steady stream of exciting discoveries over the next few years," Mahadevan said.

The second SDSS-III survey whose data Penn State scientists will study with the Hobby-Eberly Telescope is the APO Galactic Evolution Experiment (APOGEE), which is using one of the largest infrared spectrographs ever built to undertake the first systematic study of stars in all parts of our Galaxy -- and even of stars on the other side of our Galaxy beyond the central bulge. Such stars typically are difficult to study because their visible light is obscured by large amounts of dust in the disk of our Galaxy. However, by working at longer, infrared wavelengths, APOGEE can study them in great detail, thus revealing their properties and motions to explore how the different components of our Galaxy were put together.

"The SDSS-III is an amazingly diverse project built on the legacy of the original SDSS and SDSS-II surveys," said Bob Nichol, the scientific spokesperson for the SDSS-III collaboration. "This image is the culmination of decades of work by hundreds of people, and it already has produced many incredible discoveries. Astronomy has a rich tradition of making all such data freely available to the public, and we hope everyone will enjoy it."

More extensive information about the new SDSS-III terapixel image is available at online.

  • This illustration shows the wealth of information on scales both small and large available in the SDSS-III's new image. To see a high-resolution version, click on the image above.

    IMAGE: Penn State
Last Updated March 21, 2011