Hopkins Astronomers on Science Team Designing Historic Telescope
The National Science Foundation last month awarded the grant for the Sloan Digital Sky Survey, a $30 million project involving scientists from The Johns Hopkins University and other institutions in the United States and Japan. Astronomers will use the telescope to map the cosmos, gathering unprecedented volumes of information to answer a question scientists have been asking since the earliest days of cosmology: what is the large-scale structure of the universe?
"The Sloan project is arguably the most exciting of the currently planned long-term projects in ground-based astronomy," said Alexander Szalay, a Hopkins professor of physics and astronomy who is working on software for the project.
Astronomers will use the observatory, under construction in south-central New Mexico, to survey as many as 100 million galaxies and stars, some farther than 3 billion light years away. Astronomers plan to home in on the brightest 1 million galaxies, using a spectrograph to reveal highly accurate details about their distance, age and composition, Dr. Szalay said. "About two or three months into the project, we will have more data than all astronomy had before," he said.
The survey, expected to take about five years to complete, will dramatically increase knowledge about galaxies. The best sky surveys now contain 2 million galaxies, but astronomers have reliable distance measurements for as few as 20,000 galaxies. Construction on the observatory began during the summer of 1993, with initial funding of $8 million from the Sloan Foundation. Scientists expect to begin testing the 2.5-meter telescope within a year and have it fully operational in about two years. It is located at Apache Point, near Sunspot, N.M.
Hopkins scientists will design and build the telescope's spectrograph, an instrument that will enable astronomers to study about 100,000 quasars, or quasi-stellar radio sources, extremely distant objects that look like stars when viewed through conventional telescopes but are actually hundreds of times brighter than an entire galaxy, said Hopkins research scientist Alan Uomoto, project scientist for the team designing the spectrograph. Other Hopkins researchers working on the instrument are astronomy professor Paul Feldman, research scientist Scott Friedman and mechanical engineer Stephen Smee. By mapping the cosmos in detail, astronomers will learn how galaxies are organized into clusters and "superclusters," which ultimately will help cosmologists understand more about the processes leading to the present structure of the universe. The telescope will be extremely sensitive to distant light because its focal plane will be lined with charge-coupled devices (CCDs), light-sensor chips used in video cameras that enable scientists to capture an image accurately. The typical large telescope has one CCD in its focal plane, but the Sloan telescope will contain 54 of the devices, 30 in the focal plane alone.
The survey will cover half of the northern sky -- or a quarter of the total sky -- since the other half is obscured by the bright, nearby plane of our own galaxy. Dust in the Milky Way blocks much of the light coming from distant galaxies, so scientists have to look away from our galaxy to see those objects.
Another major part of the project will be to make the volumes of information available to scientists and non-scientists. Over five years researchers will collect 12 to 20 trillion bytes, enough data to fill 10 million floppy disks. Just one night of observations will provide a few thousand floppy disks' worth of data, said Dr. Szalay, who is working with a team of Hopkins scientists that includes professors Tim Heckman, Holland Ford and Rosemary Wyse, postdoctoral fellows Andrew Connolly and Michael Vogeley and graduate students Robert Brunner, Kumar Ramaiyer and Gyula Szokoly.
Most of the sky survey information will be placed in a digital archive, probably in the form of 500 to 1,000 compact discs, which will be made available to the public. It will be the first extensive compendium of astronomical data recorded originally in digital form. Many other sets of data in existing archives have been converted from original photographs into digital images for computer storage, reducing the clarity of the images. Scientists foresee a user-friendly system that will provide access to a huge amount of information simply by clicking a mouse, revealing the images, and recalling other important properties of the objects on the screen.
The project is being managed by the non-profit Astrophysical Research Consortium. University of Chicago astrophysicist Donald G. York is heading the collaboration of scientists. Also involved are Princeton University, the Institute for Advanced Study, the University of Washington, Fermi National Accelerator Laboratory, the Naval Research Observatory and a group of Japanese astronomers.
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