Gian Domenico Cassini formulates Cassini’s Laws, three …

Years: 1695 - 1695

Gian Domenico Cassini formulates Cassini’s Laws, three empirical rules that accurately describe the rotation of the Moon, in 1693.

They are: (1) the Moon rotates uniformly about its own axis once in the same time that it takes to revolve around the Earth; (2) the Moon's equator is tilted at a constant angle (about 1°32¢ of arc) to the ecliptic, the plane of Earth's orbit around the Sun; and (3) the ascending node of the lunar orbit (i.e., the point where the lunar orbit passes from south to north on the ecliptic) always coincides with the descending node of the lunar equator (i.e., the point where the lunar equator passes from north to south on the ecliptic).

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