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Re: Equinoxes



At 20:31 10/18/97 -0700, David Abineri wrote:
When was precession of the equinoxes first observed and how was the
observation made? When was it verified?

The discovery is attributed by Ptolemy to Hipparchus, ca. 135 BC.
Hipparchus must have had access to the measurements of an earlier
observer.
...
Leigh


This is how Claud of Ptolemy describes it in the Almagest, book 3:

"Since finding the year's time-length is the first of all the things
demonstrated concerning the Sun, we shall first learn from the treatises
of the ancients the disagreements and difficulties concerning their
statement on this, and especially from that of Hipparchus, a diligent
and truth-loving man. For he is brought to a difficulty of this kind
especially by the fact that, for the apparent returns of the Sun with
respect to the tropics and equinoxes, the length of the year is found
to be less than 365 1/4 days, but for its returns observed with respect
to the fixed stars it is found to be more. And from that he conjectures
that the sphere of the fixed stars also has a very slow movement, and
like that of the planets is in the direction contrary to that of the
prime movement which revolves the circle that passes through the poles
of the equator and the ecliptic..."

Later Ptolemy writes in book 7:

"...And Hipparchus first, from the appearances he had, [...] for the most
part conjectured rather than affirmed them because of the very few
observations on the fixed stars that had been made before him, which were
only those recorded by Aristyllus and Timocharis and which were uncertain
and not worked over. And we, from a comparison of what is observed now
with what was observed then, have come to the same conclusion "
[with a longer timebase and using Hipparchus' records bw]

(Translated from the German Heiberg edition of Manitius by Taliaferro.)


I have no copy of Hipparchus, but can finally provide this direct
quotation from "On The Precession Of The Tropic And Equinoctal Points"
by that author:
"If then, for example, Spica was formerly 8 degrees in longitude
west of the autumnal equinox and is now 6 degrees west..."

Sincerely,
Brian
brian whatcott <inet@intellisys.net>
Altus OK