iSGTW Feature - The Big Picture

Feature: Caltech and TeraGrid See the Big Picture

The Samuel Oschin telescope at the Palomar Observatory in California.
Courtesy of Palomar Observatory.

The Griffith Observatory in Los Angeles recently unveiled a spectacular new display during its grand re-opening. The "Big Picture," an image of the Virgo Galaxy Cluster 150 feet wide and 18 feet high, recorded for posterity on porcelain-enameled steel tiles, was created using data from the Palomar-QUEST sky surveys that were processed using TeraGrid resources.

"The observatory came up with this idea five or six years ago, that a single image of the sky would cover the main wall of their new exhibit hall," says Caltech astronomer George Djorgovski.

"Palomar-QUEST surveys 1.25% of the entire sky each night, and covers the same areas multiple times. By the end of the survey we'll cover 15,000 square degrees, or 40% of the entire sky." Even the Big Picture, huge by photo standards, will only show a tiny piece of the whole sky-about 30 square degrees.

Palomar-QUEST is a synoptic survey, which means that the same area of the sky is imaged several times using a different filter, similar to taking a picture of the same object one color at a time.

"Some sections were imaged up to 16 times on separate nights," explains Roy Williams from the Caltech Center for Advanced Computational Research. "Palomar-QUEST uses only a 48-inch telescope, but the computers give the effect of a much larger telescope, because they allow us to synthesize all these separate observations to make a single high quality image."

Data from the telescope were sent via high-speed network to the National Center for Supercomputing Applications in Illinois for archiving. Sections needed for the Big Picture were transferred to the computational facility at Caltech for processing. At the time, the Caltech computational facility and network to NCSA were TeraGrid resources.

Raw telescope data is not like a photo from a digital camera, it has to be highly processed to convert it into a form useable for astronomers, and additional processing is required to create a high-quality image such as the Big Picture. First the images were warped and re-projected to place all the pixels in the same frame, the intensities of the different colors were added together, artifacts were removed, images were checked against star catalogs for correct positioning, then images from different nights added together, and finally detailed touchups were done to the images.

"Millions of people every year will see this at the observatory," says Djorgovski. "We've also developed a companion Web site that will serve as a gateway to virtual astronomy and physics. We'll tie it in to information technology and the grid, as this was a nice testbed project in many ways for a variety of massive grid applications, both scientific and educational."

- Katie Yurkewicz, iSGTW