15. The Zodiac

Yesodei HaTorah 3:5

The total number of spheres that surround the Earth is 18; the number of smaller spheres that do not surround the Earth is eight. The number of spheres and their orbits are calculated by observing the movement of the planets combined with our knowledge of their revolutions, their position in the sky, and their distance from Earth. This is the science of astronomy, about which the Greeks wrote many works.

Yesodei HaTorah 3:6

The ninth sphere - the outermost sphere - was divided by the Sages into twelve sections. Each of these sections was given a name suggested by shapes formed by the stars that appear in that section. These are the constellations: Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces.

Editor’s note: I am not able to explain the Rambam’s astronomy. In Hilchos Kiddush HaChodesh (17:24), he says that it is based on the science of Greek astronomers. In Moreh Nevuchim, he is willing to disregard Talmudic dicta (3:14) and even Biblical verses (2:25) in favor of observable science when necessary. Readers are free to assume either that the Rambam was sharing the best science of his day, or that he is describing spiritual rather than physical phenomena.