23: 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. However, the ancients 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.