One of the greatest limitations of ground-based astronomy is the fact that Earth's atmosphere ever-so-slightly distorts light traveling through it. When viewing large objects or regions of the sky, the distortion is not tremendously troublesome, but as astronomers try to view smaller and smaller areas of the heavens, the distortion becomes more and more noticeable.
This is the problem that created the demand for a space-based telescope that could rise above the turbulent atmosphere to capture clean, clear pictures of faraway celestial objects.
But developments made during the past decade in the field of adaptive optics are enabling astronomers to make corrections for the blurring effects of the atmosphere to get images that are competitive in clarity with the Hubble Space Telescope (HST).
"Image quality, which was once the sole realm of the HST is now being challenged by adaptive optics on telescopes on the ground," said Buzz Graves, an astronomer at the University of Hawaii and an expert in adaptive optics.
The key is to use a deformable mirror that can be manipulated as many as a thousand times a second to compensate for any blurriness the air causes.
Areas of cold and warm air mixing in the atmosphere can be compared to a series of lenses, said Graves: "These lenses are changing shape as turbulence occurs. Each little lens section in the atmosphere de-focuses a star in one way or another."
The effect occurs over scales of about 12 inches, "so from one 12-inch patch to another 12-inch patch -- or column in the atmosphere -- you might have a different lens. And these are constantly changing in time," explained Graves "So you need to have a deformable mirror which can just put in the opposite of what the atmosphere put in. The end result is you get good vision, the same way you put corrective lenses on your eyes."
To automatically correct for the atmosphere's blurring effects, an adaptive optics mirror needs to be bent and manipulated 1000-times-per-second.
The results are impressive.
"A telescope with adaptive optics will outperform a telescope three times bigger. It's just because the light, which would normally be spread out in this blurry blob, can now be collapsed into a very sharp point," said Graves.
With such a giant leap in performance possible with relatively little cost, observatories around the world are scrambling to develop adaptive systems.
"Every large telescope on the face of the Earth -- if it doesn't have one operating right now -- has one that's being worked on," noted the astronomer. "There's simply no facility, no matter what size, that hasn't considered adaptive optics."
In such a booming field, the rush is on to develop the best system--and the fight for funding is fierce.
"It's very competitive," observed Graves. "Everybody thinks they've got the best mousetrap."
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