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Old October 21st 18, 06:35 AM posted to sci.astro.amateur
Barry Schwarz[_2_]
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Default OT? Amateur Astronomy

On Sat, 20 Oct 2018 08:05:02 -0700 (PDT), Quadibloc
wrote:

On Thursday, October 18, 2018 at 11:35:06 PM UTC-6, Gerald Kelleher wrote:

A person capable of using their intelligence will recognise that the RA/Dec
framework is in competition with the Lat/Long system for the basic answer to the
question 'How long does it take the Earth to turn once ?'. The reasonable answer
is once in 24 hours with quite a long explanation covering timekeeping from its
emergence in antiquity to demonstrate the rules which tie cyclical timekeeping
to cyclical dynamics to a close approximation.


The naive answer is indeed 24 hours.

If the Earth didn't turn, wouldn't one part of the Earth always face the Sun,
the way Mercury was once thought to do, and the way one side of the Moon always
faces the Earth?


If the Earth didn't turn at all, then the time from one sunrise to the
next would be approximately 24*365.25 hours. One side of the Moon
always faces the Earth precisely because its rotation about its axis
"exactly" matches it revolution around the Earth.


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