Section 2: The Moon – Earth’s Satellite
The gravitational pull of Earth on the moon causes the moon to move in an orbit around the Earth. The changing relative positions of the moon, Earth, and sun cause the phases of the moon, eclipses, and tides. The different forms of the moon you see from Earth are called phases. The sequence of phases is the lunar cycle, which lasts 295 days. The phase of the moon you see depends on how much of the sunlit side of the moon faces Earth.
An eclipse is when the Earth or the moon casts a shadow on the other. A solar eclipse is when the moon’s shadow appears on the Earth’s surface. A lunar eclipse occurs when the moon moves into Earth’s shadow.
The moon has unique features on its surface, including craters, maria, and highlands. Craters are large, round pits caused by impacts of meteoroids, which are chunks of rocks from space. The dark, flat areas that formed from lava billions of years ago are called maria. It also has highlands, which are old and the most highly cratered regions on the moon.