Re: how did the ancient greeks know that the sun (or earth's) orbitwas not circular?

canopus56 wrote:
>

> To measure the position of the Sun, it's declination could be
> determined at noon by measuring the angle that the shadow cast by the
> Sun against a vertical stick.

got it.

> At night when the Moon is at it's first
> and second quarters, the position of the Sun can be ascertained by
> determining the nighttime right ascension of the Moon.

If I put a bit of time into it, I can by looking at the fuzzy
terminator against blue sky just after sunset, differentiate
a full moon from a moon 24 hours away from a full moon,
but that's about as good as I can get. Presumably the Greeks
had much better accuracy than that. How did they do it?

How do you tell that the moon is at 1st or 3rd quarter? Holding
up a ruler to compare the size of the dark and light halves?
Looking at the curvature of the terminator?

Presumably any of these measurements would be confounded by
parallax?


> - dioptra << http://members.tripod.com/Bluestar_4/Dioptra.html >>
> << http://members.tripod.com/Bluestar_4/Dioptra.html >>

I didn't get how this worked. Will need to spend a bit of time on it.

> - equatorial ring
> <<
> http://www.fas.harvard.edu/~scdiroff/lds/AstronomyAstrophysics/EquatorialRing/EquatorialRing.html
> >>

so how do you set this to the plane of the celestial equator
in the first place? Do you watch stars near to the equator and
see that they move parallel to the ring. Presumably you could
set up an armillary sphere and get your north pole from that.
Still they'd need an accuracy of at least a degree to detect
a difference of 2-3 days in the seasons.

> http://en.wikipedia.org/wiki/Hipparchus_%28astronomer%29

smart fellow. I would have trouble reproducing his work with
a PC.

Joe

--
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
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Homepage http://www.austintek.com/ It's GNU/Linux!
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