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ADAPTIVE OPTICS FROM THE PERSEIDS
ASTRONOMERS CAN benefit from air pollution—provided it’s cleverly exploited in what’s called “adaptive optics.” The topic is most appropriate at this time, as we’re at the high point of the annual Perseids meteor shower (California’s peak: 5 a.m. Pacific, today, Monday, August 12).
When a particle encounters the atmosphere, it’s traveling at perhaps 130,000 mph. It’s this speed, not the particle’s size, that determines the energy of a “shooting star.” The meteor also leaves a trail of sodium, traces of which end up in a band encircling the Earth at an altitude of about 55 miles.
American astronomer Vesto Slipher of the Lowell Observatory, Flagstaff, Arizona, discovered this band, the sodium layer, in 1929. (He and his brother, fellow astronomer Earl, have craters named after them on the Moon and Mars.)
In the 1950s, astronomers began fooling with “guide stars,” researcher-generated light sources used to sharpen celestial images. By the 1980s, the military was tracking Soviet satellites with enhanced precision—and this technology of adaptive optics went Classified. A decade later, the scientific community got it declassified.
Adaptive optics corrects for the inherent turbulence of the atmosphere, something that affects any Earth-bound observation.
AO (adaptive optics) transforms a fuzzy image into a sharp one. Image from the University of Arizona; see http://goo.gl/p9pyRr.
Lasers are used to excite the sodium layer, thus creating the guide stars. Sensors monitoring these artificial sources of light see them twinkling through the atmospheric turbulence. Computer algorithms analyze the turbulence and send these data to the telescope. Mirrors within its optics, operating at hundreds of times per second, account for the turbulence—and the result is a sharper image.
The technology of adaptive optics has been called the greatest advance in Earth-based astronomy since Galileo’s first telescope 400 years ago.
Galileo shows the Doge of Venice, seated, how to use a telescope, c. 1609. Fresco by Giuseppe Bertini, 1858.
The Perseids, an enormous cloud of pebbles and space dust, collide with Earth on an annual basis, typically in early August. Their shooting stars enhance the sodium layer as well as provide great viewing. During the Perseids’ height, it’s possible to see 80 meteors per hour.
Perseids meteor, photograph by Pierre Martin, August 12, 2006. Image from NASA; see http://goo.gl/uEK4xl.
Wife Dottie and I recall fondly the Perseids shower a while back during the week of historic car activity along California’s Monterey Peninsula. That year we took the Miata, and its top-stowed viewing opportunities were ideal. We searched out a dark corner adjacent to the golf course at Quail Valley Lodge, got comfy leaning back and awaited the shower.
It was an enchanting hour and a half, the sky was ink-black in its clarity—and we saw nary a single Perseids meteor. We were captivated, though, by the number and regularity of man-made satellites, easily distinguished from aircraft by their rapid pace across the sky.
We learned later it was something of a bum year for the Perseids. No matter, it was still magical for us. ds
© Dennis Simanaitis, SimanaitisSays.com, 2013
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