[time-nuts] telling time without a clock
jimlux at earthlink.net
Wed Jan 25 23:38:06 EST 2012
OK.. without getting into celestial navigation, the whole thing of
telling time with the moon is intriguing. And with some forethought and
data available today, we could fairly easily do what folks back in the
18th century could not.
Let's say you run a suitable celestial model and identify all the
reasonably bright and identifiable star that the moon occults in a given
day. The moon moves about 1/2-1 degree per hour against the star field,
so the question is, could you find, say, a star every couple hours.
Then, assuming you know *about* what time it is, say, 930PM, you can go
to your table, see that the Moon occults zeta obscuris at 2143. You sit
there with your binoculars and watch the moon, and when zeta obscuris
disappears, you know it's 2143. Done.
You could even do it automatically with a not very accurate "goto"
telescope and a camera (you just have to be able to point to the correct
limb of the moon and look for the star).
This kind of search would be incredibly tedious if you didn't have
automation to help, but today, with reasonably accurate star catalogs
AND reasonably accurate numerical ephemerides, it should be possible to
make a "time almanac" with a page for each day, etc.
(obviously, this only works about half the day, when the moon is up)
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