Re: Astronomy - History

[palmer@sfu.ca (Leigh Palmer)]

> Are you sure you have indeed produced an ellipse, in the mathematical
> sense, or just a shape which is generally elliptical.  Kepler's problem
> what that try as he may, he could not account for the appearance of the
> orbit of Mars with sets of circles, and in the end had to use a
> non-circular device, the ellipse.  This suggests that ellipses cannot be
> made from constructions of circles...but as has happened the the past, I
> could be wrong.

Al did indeed produce an ellipse, but of course an ellipse was *not* the
goal (known or unknown) of the ancient astronomers. They were modelling
a geocentric cosmology. They had to produce a trajectory which looped
back on itself to model the appearances. Al's construction (which is an
ellipse by my reckoning) does not do that because his angular speeds are
equal and opposite in sign, two attributes which differ freom Ptolemy's.

Leigh