ВНИМАНИЕ!На форуме начался конкурс - Астрофотография месяца: АПРЕЛЬ!
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Date: Thu, 18 Oct 90 14:09:00 PDTFrom: greer%utdssa.dnet%utadnx@utspan.span.nasa.gov... The prime meridian for the Moon is defined as the line on the Moon'ssurface that would always appear straight when viewed from the Earth if theMoon's libration were zero. In other words, it goes through the middle ofthe face pointing toward the Earth. For Mars, the the crater Airy is centered at exactly 0 degreeslongitude, 0.5 degrees latitude, so I assume this is the definition of theprime meridian there. The prime meridian of Venus goes through Maxwell Montes, goes justeast of a small but well defined mountain called Eisila near the equator,and also passes through Alpha Regio. Judging from the name, I would guessthat some point in Alpha Regio defines zero degrees longitude for Venus. The prime meridian of Mercury doesn't seem to pass exactly throughanything, so I couldn't even guess at its definition.... All the mapped moons of the solar system have longitude defined, butjust looking at the maps it usually isn't obvious why the prime meridian iswhere it is. Probably the U.S. Geological Survey has a pamphlet explainingthis sort of thing.