Earth and Moon

Psalm 89:36-37

“His seed shall endure for ever, and his throne as the sun before me. It shall be established for ever as the moon, and as a faithful witness in heaven. Selah.”  

Strictly speaking, the Moon does not orbit the Earth. Let me explain. The Moon is actually a large body compared to the Earth. It is the fifth largest natural satellite in the Solar System. Only three moons of Jupiter (Ganymede, Callisto and Io) and one moon of Saturn (Titan) are larger. In fact, it is the 14^th largest object in the Solar System. Its volume is 2% that of the Earth, and its mass 1%. So it is a very significant size compared to the Earth. That means that the Moon doesn’t really orbit the Earth. Both Earth and Moon orbit a common center of gravity. However, that center of gravity is within the surface of the Earth.

This large size for the Moon, compared to its host planet, means that Earth and Moon affect each other greatly. The Earth’s gravitational pull on the Moon is such that it maintains a synchronous orbit, where its rotation on its axis occurs at the same rate as its orbital period. The practical result of this is that one side of the Moon is constantly facing the Earth, while the other constantly faces away.

The Moon’s gravity affects the Earth by pulling somewhat on the oceans, causing a bulge, which is what gives us our tides. These tidal forces also operate on the land but are not so noticeable.

God made the Moon special and caused it to be the faithful witness in the sky, “dying” for three days, then rising again.

Prayer: You have planned everything perfectly, Lord, even down to the details of creating the Moon just right to have the right sort of effects on the Earth. Amen.

Author: Paul F. Taylor

Ref: Encylopædia Britannica, < https://www.britannica.com/place/Moon >, accessed 12/27/2018. Image: NASA, Public Domain.

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