23.0 The Planets

Most stars we observe form fixed constellations in the sky, undergoing daily motion (e.g. rising and setting) but maintaining fixed positions relative to each other --- like the stars of Orion, or the Big Dipper. The ancients however noted that 5 stars constantly moved --- all following close to the paths of the Sun and Moon across the heavens, i.e., close to the ecliptic. The Greeks called them planets, Greek for wanderers, a name still used.

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