A few years ago, I decided that I needed to know more about the
history of science, so naturally I volunteered to teach the
subject. In working up my lectures, I was struck with the fact
that in the ancient world, astronomy reached what from a modern
perspective was a much higher level of accuracy and
sophistication than any other science. One obvious reason for
this is that visible astronomical phenomena are much simpler and
easier to study than the things we can observe on the earth’s
surface. The ancients did not know it, but the earth and moon
and planets all spin at nearly constant rates, and they travel
in their orbits under the influence of a single dominant force,
that of gravitation. In consequence, the changes in what is seen
in the sky are simple and periodic: the moon regularly waxes and
wanes, the sun and moon and stars seem to revolve once a day
around the celestial pole, and the sun traces a path through the
same constellations of stars every year, those of the zodiac.
Even with crude instrumen