Thomas Fly wrote: > .... > It's hard to say (without writing a computer program to calculate it) precisely > what "after shadow" means, because of the earth's atmosphere. It's fairly well > known (among amateur astronomer types) that at sea-level, etc., a "horizontal" > light ray has been refracted by about 35 minutes of arc, so that the setting > sun/moon (having a diameter of about 30 minutes of arc) is in fact entirely > below the physical (i.e., unrefracted) horizon when it first begins to "set." > ... > So the atmosphere acts somewhat as a lens (or prism), bending the light from the > sun into what would otherwise be "shadow." ...and remember that for a satellite entering shadow this effect is doubled as a light ray which just skims the Earth's surface would be refracted twice, once on the way into the atmosphere and once on the way out. ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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