Friday, January 9, 2009

Two views of the moon

These are two images of Copernicus crater on the Moon. The first, taken with a space probe, and the other taken with a large amateur telescope. Probably the most impressive thing to see is that the earth based images are quite good. Looking at similar features on the Earth, from the moon, would be very difficult indeed due to weather conditions on earth. But going in either direction, having to pass through an atmosphere is a significant limitation. Seeing is what limits most telescopes on earth, while most space telescopes are technically limited, or diffraction limited like the Hubble Space Telescope which is to say, they work at the limit of what is possible for the given optical gathering surface.

Note the red lines; these are a rough guess at the scope of the first, higher detail image. Not bad for government work.

"Lunar Orbiter II recorded this image at 7:05 p.m. EST on November 24, 1966, from 28.4 miles above the Moon's surface, and about 150 miles due south of Copernicus. The clarity of the view is attributable to the absence of atmosphere. A photograph from similar altitudes of distant features on Earth would never be as sharp, because of haze.

Copernicus is about 60 miles across and 2 miles deep: 3000-foot cliffs, apparently landslide scarps, can be seen. Peaks near the center of the crater form a small mountain range, about 1500-2000 feet high and 10 miles long."

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