Kepler

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CHAPTER I.

ASTRONOMY BEFORE KEPLER.


In order to emphasise the importance of the reforms introduced into
astronomy by Kepler, it will be well to sketch briefly the history of
the theories which he had to overthrow. In very early times it must have
been realised that the sun and moon were continually changing their
places among the stars. The day, the month, and the year were obvious
divisions of time, and longer periods were suggested by the tabulation
of eclipses. We can imagine the respect accorded to the Chaldaean sages
who first discovered that eclipses could be predicted, and how the
philosophers of Mesopotamia must have sought eagerly for evidence of
fresh periodic laws. Certain of the stars, which appeared to wander, and
were hence called planets, provided an extended field for these
speculations. Among the Chaldaeans and Babylonians the knowledge
gradually acquired was probably confined to the priests and utilised
mainly for astrological prediction or the fixing of religious
observances. Such speculations as were current among them, and also
among the Egyptians and others who came to share their knowledge, were
almost entirely devoted to mythology, assigning fanciful terrestrial
origins to constellations, with occasional controversies as to how the
earth is supported in space. The Greeks, too, had an elaborate mythology
largely adapted from their neighbours, but they were not satisfied with
this, and made persistent attempts to reduce the apparent motions of
celestial objects to geometrical laws. Some of the Pythagoreans, if not
Pythagoras himself, held that the earth is a sphere, and that the
apparent daily revolution of the sun and stars is really due to a motion
of the earth, though at first this motion of the ear