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CHARA Observatory Comes into Focus
By Andrew Bridges
Pasadena Bureau Chief
posted: 03:30 pm ET
05 October 2000
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chara_dedication_001005 MOUNT WILSON, Calif. -- Georgia State University dedicated its Center for High Angular Resolution Astronomy observatory on Wednesday, a $13.8 million array of telescopes powerful enough to resolve details 200 times finer than the Hubble Space Telescope.When completed, the interferometric array known as CHARA will command its six, 40-inch (1-meter) telescopes -- scattered across the summit of 5,700-foot (1,737-meter) Mount Wilson -- to act in concert, mimicking the properties of a single telescope hundreds of times larger. For now, four years after work on the observatory began, just three of the telescopes are operational. 
Inside one of CHARA's six telescope domes. But when all six telescopes are on line, CHARA will allow astronomers to make high-resolution studies of nearby stars, revealing them with a clarity few other observatories can match."They will be able to see things they only imagined up until now," said Carl Patton, university president. Georgia State funded the observatory with grants from the National Science Foundation, W.M. Keck Foundation, David and Lucile Packard Foundation and private donations. The Atlanta-based university originally sought to place the observatory elsewhere in the Southwest, but ultimately settled on Mount Wilson. The lofty peak, located just north of downtown Los Angeles, is home to several all-but-superannuated telescopes, including the 1917 Hooker 100-inch (2.5-meter) instruments. However, in its heyday, the Hooker was the worlds most powerful telescope, used by the likes of Edwin Hubble in the mid 1920s to prove the universe is expanding. Robert Jastrow, director of the Mount Wilson Institute, said CHARA would help return the peak to prominence. ~ "CHARA, which in terms of aperture and baselines combined is the worlds most powerful optical interferometer, restores Mount Wilson to the cutting edge of contemporary astronomy," Jastrow said. Although located near some of the smoggiest air in the country, Mount Wilson prides itself on its excellent "seeing," thanks to the stable air that flows in from the Pacific Ocean over the peak. Although far from Georgia, the observatory will be a hands-on instrument for university members. 
Two of the vacuum pipes that carry light to the central beam synthesis facility from CHARA' s six telescopes. "Eventually, the plan is the whole facility can be operated from Atlanta," said Theo ten Brummelaar, a senior research scientist at Georgia State. The arrays six telescopes, arranged in a "Y," will collect light from the same target star before sending it traveling up to 660 feet (200 meters) through vacuum pipes to a central beam-synthesis facility. There, the beams are trimmed, so to speak, so the path length of each is even to within millionths of an inch (centimeter). The beams are then combined, creating a phenomenon called "interference," which gives the instrument its name. The process creates semicircular patterns of light and dark bands, called fringes. By examining the fringes, the brightness and position of which is mathematically related to their source, astronomers can learn more about a stars shape and structure. CHARA achieved its first fringes in November 1999. "I can assure you, with relief, that this thing does work," said Hal McAlister, the CHARA director. Astronomers hope to use CHARA to measure the diameters and surface temperatures of stars, detect companion orbiting stars and measure the mass of such binary systems. The array will also allow them to seek out planets and brown dwarfs in multiple star systems. CHARA is but the first of three large optical interferometers to come on line in the near future. The Keck Interferometer in Mauna Kea, Hawaii and the Very Large Telescope Interferometer in Paranal, Chile will soon join it. And NASA and the European Space Agency are both planning space-based interferometry missions, including the Space Interferometry Mission, Space Technology 3, Darwin and the Terrestrial Planet Finder.
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