The Moon is made up of solid rock. The surface consists of mountains, peaks and craters, deep valleys and plains. The plains of the Moon are also called maria. The Moon does not have water or atmosphere, and is not suitable for existence of life. Although seen at night, the moon may also be present in the sky during the daytime, but the Sun is generally bright enough to hide it. The Moon takes about 27 days to rotate once on its axis, and about the same time to revolve around the Earth. As a result, the same side of the Moon always faces the Earth. The Moon is the only celestial body ever visited by humans. In July 1969, the American Astronauts Neil Armstrong and Edwin Aldrin became the first men to land on the surface of a celestial body. As their spacecraft Apollo 11 descended onto the Moon’s surface, they saw the beautiful sight of the Earth rising above the horizon of the moon. Neil Armstrong became the first man to step onto the surface of the Moon.