Page 196 - 89 history of astronomy_opt

Ptolemaic, the Copernican, and the Tychonic.
The two latter placed all of the planetary
orbits concentric with one another, the sun
being placed a little away from their com-
mon centre, and having no apparent rela-
tion to them, and being actually outside
the planes in which they move. Kepler’s
first great discovery was that the planes of
all the orbits pass through the sun; his sec-
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