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Re: Lunar eclipse report
From: Herbert Prinz
Date: 2004 Oct 30, 19:51 -0400
From: Herbert Prinz
Date: 2004 Oct 30, 19:51 -0400
Frank Reed wrote:
> All you need is a careful observation of the sidereal time (which is
> the right ascension of the zenith). With a fixed installation, you
> could mount a sight tube. For a temporary setup, you could hang a
> couple of plumb lines and stand between them extending the lines. This
> should give local sidereal time within two minutes or better. Assuming
> roughly two minutes error in eclipse event timings and two minutes
> error in local time, the average expected error would be about three
> minutes --less than a degree error in longitude.
I understand that in the context of your message, this was only meant as
an estimate of a theoretical best case scenario ("IF the need had arisen
..."). In actual practice, however, the REAL problem was to measure
elapsed time between the celestial signals (eclipse phases, occultation,
whatever) and the events that established local time (meridian
transits). In antiquity, local time would more likely have been
established by sun observation than from the stars. From the top of my
head, Strabo acknowledges this, but I can't dig out the reference now.
Herbert Prinz
