Re: Coordinates on mars


William Hamblen wrote:
On 14 Jul 2006 01:26:57 -0700, mike4ty4@xxxxxxxxx wrote:

Why is longitude on Mars measured 360 degrees all the way around, going
west, instead of like on Earth where we have two zones of 180 degrees
each, going both east and west? Why don't we uniformize these systems?

Longitudes on all the planets other than the Earth is measured that
way because it is simpler for astronomical observations. One thing
about Mars is that there are two coordinate systems in use and
measurements in one are slightly different from measurements in the
other. Selenographic and lunar coordinates on the Moon work like
latitude and longitude on maps of the Earth. This makes since because
the Moon always presents the same face to the Earth with the zero
point more or less in the middle of the disk. Lunar coordinates have
east and west defined as they look in the sky. The sun rises in the
west on the Moon in the lunar coordinate system. Selenographic
coordinates have east and west defined as they look on the Earth, The
sun rises in the east on the Moon in the selenographic coordinate
system. Longitude is measured on the Earth the way it is for historic
reasons. I suppose it might be easier for navigation, too.

How does it simplify astronomical observations? And what "historic
reasons" are there to keep the current system for Earth?

.

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