Re: [Humour]: People actually said these things

Paul S. Walsh wrote:
> Speaking of which, here is a very nice primer on Kepler's laws for those who
> are unfamiliar with them or, like me, who might need to brush up on the
> third one :-)
>
> http://csep10.phys.utk.edu/astr161/lect/history/kepler.html

That's quite a nice page.

Here's one additional tidbit: The orbit of Mars does confirm Kepler's
laws, but only barely. Despite using circular orbits, Ptolemy's model
nevertheless incorporated some features of the elliptical orbits of
Kepler's laws, such as that the Earth is not at the precise center of
the Sun's orbit (reversed, of course, in the heliocentric model), but
is off-center; and that the revolving object moves faster when closer
to the central body and slower when further away. Provided that we
put the Sun at the center of the solar system and not the Earth, this
model of circular orbits would explain Mars's path across the skies
very well. The error is probably measured in arcminutes--beyond the
accuracy achievable in Ptolemy's time (and long afterward).

Brian Tung <brian@xxxxxxx>
The Astronomy Corner at http://astro.isi.edu/
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.

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