The document discusses the relationships between the Earth, moon, and sun. It explains that the moon's rotation is synchronized such that the same side always faces Earth. The moon affects Earth's tides and orbital motion. While the sun gravitationally influences Earth and the moon as a single system, Earth's elliptical orbit and changing rotation rate mean the sun's position is not uniform from Earth's perspective. Therefore, mean solar time uses a theoretical mean sun point that moves at a constant rate instead of the real sun's position.