Earth-Moon system
Quick Summary
The Earth-Moon system consists of our planet and its natural satellite, the Moon. The Moon is a rocky sphere with a radius of about 1,738 kilometers (1,080 miles). It is relatively massive for a satellite, exerting a significant gravitational influence on Earth, which causes tides and affects the length of our days.1
The Moon and Earth orbit a common center of mass, known as the barycenter, which is located within Earth. The gravitational pull of the Moon, along with the Sun, is the primary cause of ocean tides. The Moon's phases, such as new moon and full moon, are a result of its orbital geometry with Earth and the Sun. Eclipses, both solar and lunar, also occur due to the alignment of these three celestial bodies.123
The origin of the Moon is still a subject of scientific theories, including coaccretion, fission, capture, and impact hypotheses involving a Mars-sized body named Theia.4
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