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New Observatory Brings Stars Closer to Earth
String of Telescopes Link Up to Boost Star-Viewing Powers
 Listen to Joe Palca's report.
Naval Observatory astronomer Don Hutter, left, and NPR's Joe Palca inside one of the telescope shelters.
Photo: Mitch Teich, KNAU
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An aerial view of the Y-shaped Navy Prototype Optical Interferometer.
Photo: NPOI
 Enlarge image
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One of the NPOI telescopes on the Y-shaped array.
Photo: Mitch Teich, KNAU
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Three parallel aluminum pipes, which look deceptively like a fence, carry beams of light captured by each of the telescopes stationed along the array. The light beams are then combined, providing a more detailed view of the stars than any single telescope could produce.
Photo: Mitch Teich, KNAU
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June 14, 2002 --
A new observatory based on an old concept is nearing completion outside Flagstaff, Ariz. Instead of a single, large telescope, the new observatory combines the light from several telescopes at once, providing a more detailed view of stars than any single telescope could produce on its own. As NPR's Joe Palca reports for Morning Edition, it's taken more than 100 years to pull it off.
In 1868, French physicist Hippolyte Fizeau first proposed the idea of combining light from multiple telescopes. He showed that the technique could theoretically be used to measure the size of stars. But bringing beams of light together in exactly the same place and at precisely the same time -- a technique called interferometry --- proved devilishly difficult, and was largely abandoned until recently.
Now technology has caught up with Fizeau's theory.
The U.S. Naval Observatory and Naval Research Laboratory in Washington, D.C., and the Lowell Observatory in Flagstaff are building the new interferometer, called the Navy Prototype Optical Interferometer (NPOI). The facility is huge, spreading across eight acres. From the air, it looks like a giant Y. The three arms of the Y stretch out from a central core. Along each of the arms are places where telescopes can be mounted.
Three parallel aluminum pipes, shoulder high, make up the array, giving the place the look of an oil refinery. But the pipes don't carry oil and gas, they carry beams of light. Inside the pipes, a vacuum keeps out air molecules the light would bend around.
One of the major hurdles in building an interferometer is stability. The light-carrying tunnels have to be stable to the point that, with the wind blowing, motors whirring and telescopes changing direction, no part of it can move more than a fraction of the diameter of a human hair.
That's no easy feat today, and a century ago, it was almost impossible. The high-speed computers and specialized lasers needed to make interferometry work have only recently become available.
The interferometer sits atop the Anderson Mesa outside Flagstaff, surveying the dark, clear skies of Arizona. Once the telescopes in the array pick out a star, the light travels through vacuum pipes and ends up inside a machine that splits the beams, then recombines them. The combined beam goes into a set of detectors, the modern-day equivalent of a telescope eye-piece. Computers then analyze the signal from the detectors.
Earlier this year, the facility for the first time combined the light of six linked telescopes -- the greatest feat yet in the world of interferometry.
Astronomers working with NPOI hope that once the observatory is completed, they will have the power needed to directly image the surface of stars. So far, astronomers have only been able to see the surface structure of one star -- the sun.
The interferometer can also help establish precisely where a star is. That's why, back on Earth, the Navy is interested enough to invest $30 million in the observatory. It plans to use the interferometer to help perfect its navigation systems.
In Depth
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Resources
• Navy Prototype Optical Interferometer
• Lowell Observatory
• U.S. Naval Observatory
• Naval Research Laboratory
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