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Old 08-08-2008, 12:23 PM
Sharnbrook (Mike)
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Sharnbrook is offline
 
Join Date: May 2006
Location: Toowoomba
Posts: 364
G'day all,

From the Google Earth line, I shall be 7.3km away from the direct pass, and Starry Night shows that I shall just miss the transit of the Moon, but I shall try to capture it one way or another.

However, my dilemma is what exposure to use? HST has a magnitude of .22, and the Moon tonight is -11.78, giving a differential magnitude of 12.0. This equates to approximately 64000 times as bright. Presumably, all we are going to get is a black dot as the HST passes in front of the moon, so detail isn't a problem, so expose for the moon, and hope to catch a black dot?

OK. But if HST misses the moon, as I expect it will from my location, what exposure should I give for the HST? I intend using my 40D on an 80mm Celestron ED with a focal length of 600mm. This seems to give a field of view of about 1 deg, or twice the moon's diameter, so if I don't get a transit, I should get HST going past. However, if I expose at say 1 second, the light from the moon will flood the whole view, and I shall miss out on the HST.

Any "Bright" ideas?
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