There's a new star in the sky, one made by humans to help them study other stars.
To improve the usefulness of the Keck II telescope atop Mauna Kea in Hawaii, engineers created a virtual star to aid in a complex process that adjusts for the turbulence in Earth's atmosphere in order to create better images of distant objects.
Astronomers said the artificial star, first tested Dec. 23 and announced today, should soon improve their view of distant objects, especially galaxies.
"If it works well, it should produce high-resolution images of faint objects that are otherwise inaccessible," said Harold A. McAlister, an astronomy professor at Georgia State University.
The new creation is too dim to be seen with the naked eye. In astronomical parlance, it is at magnitude 9.5, roughly 25 times fainter than what humans can see. It is made by reflecting a laser beam off a layer of sodium atoms that exist about 60 miles (95 kilometers) above Earth's surface.
On cloudless nights, the system generates a 3-foot-wide (1-meter) spot of orangish light -- similar to the color of low-pressure sodium vapor streetlights.
How it works
The artificial star caps more than a decade of efforts among astronomers, who have drawn on declassified military research to help perfect the technique.
The setup shoots a laser into the sky from a device attached to the side of the huge, 33-foot (10-meter) Keck II telescope. The laser's wavelength is designed to resonate with sodium atoms, creating a virtual star that is positioned exactly next to the real star that is the target of astronomical observation.
The light from both the real star and the artificial "guide" star, as it is known, enters the main tube of the telescope.
Light from the guide star -- which has known qualities -- is analyzed, then the light from both objects is refocused on a 6-inch (15-cm) mirror that can be deformed. The mirror is made of a thin sheet of reflective glass and can be adjusted at 349 spots. By tweaking the mirror several hundred times per second, a computer-controlled system removes blurring effects that the atmosphere has on both the guide star and the science target.
These atmospheric effects change each night, and even moment-to-moment, frustrating astronomers.
Milestone achievement
"I think it's very significant that they've successfully created the laser guide star above Mauna Kea," said Laird Thompson, a professor of astronomy at the University of Illinois. "It's a very big milestone." Thompson, who is not involved in the Keck project, is testing his own guide-star system on Mount Wilson in California.
No civilian group has yet to couple a guide star with a working telescope to make actual observations. (The Keck engineers have some details to work out before combine the virtual star with the telescope, likely this summer.)
The U.S. military did it in the late 1980s, however, Thompson said in a telephone interview. At that same time, Thompson and some colleagues were working on the idea, too, and he was involved in the first successful laser guide star, generated in 1987 -- also coincidentally on Mauna Kea.
Military researchers were surprised at the time, he said, and rushed to get their parallel efforts declassified in order to get credit for the breakthrough. The declassification of that material in the early 1990s helped civilian astronomers perfect the technique, Thompson said.
Discoveries ahead
The system that adjusts for atmospheric turbulence is called adaptive optics. Already, Keck has used it to make discoveries.
But without an artificial guide star, only very bright real stars can be used, and they must be positioned right next to a potential science target, so the technique only works in about 1 percent of the sky.
The virtual star can be placed anywhere, freeing astronomers to make better images of objects in any direction.
Keck astronomers say their
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