Space and Time
Size: Diameter 3476km
Mass: 7.35x10(exp25)kg
Mean temperature: 107°c by day, -153°c by night
Distance from Earth: 384,401km
Atmosphere/weather: None
Moon/satellites: None
Orbital period: 27.3 days
The Moon is Earth's only natural satellite. It is also the only other body in the solar system that humans have actually visited themselves. The Moon was first visited by the Soviet spacecraft Luna 2 in 1959. The American 'Apollo' missions carried a total of 12 astronauts to the Moon's surface. The first landing was on July 20, 1969, when Neil Armstrong and Buzz Aldrin became the first people to walk on the Moon. The last was in December 1972 and the last man on the Moon, so far, was Eugene Cernan of the Apollo 17 mission.
The most popular theory as to how the Moon was created is that a Mars-sized body once hit Earth and the resulting debris (from both Earth and the impacting body) accumulated to form the Moon. Scientists believe that the Moon was formed approximately 4.5 billion years ago (the age of the oldest collected lunar rocks). When the Moon formed, its outer layers melted under very high temperatures. These formed the lunar crust, probably from a global 'magma ocean.' |
Buzz Aldrin photographed on the Moon in 1969
From Earth, we see the same face of the Moon all the time because the Moon rotates just once on its own axis in very nearly the same time that it travels once around Earth. This is known as 'synchronous rotation.' Patterns of dark and light features on the nearside have given rise to the romantic 'Man in the Moon' or 'Moon Rabbit' descriptions. The light areas are lunar highlands. The dark features, called maria, are impact basins that were filled with dark lava between 4 and 2.5 billion years ago.
The Moon's surface is charcoal grey and sandy, with much fine soil. This powdery blanket is called the lunar regolith, a term for mechanically produced debris layers on planetary surfaces. The regolith is thin, ranging from about 2 metres on the youngest maria to perhaps 20 meters on the oldest surfaces in the highlands.
An astronaut's footprint in the Moon's fine soil.
The gravitational forces between the Earth and the Moon cause the tides. The Moon's gravitational attraction is stronger on the side of the Earth nearest to the Moon and weaker on the opposite side. Since the Earth, and particularly the oceans, is not perfectly rigid it is stretched out along the line toward the Moon. From our perspective on the Earth's surface we see two small bulges, one in the direction of the Moon and one directly opposite. The effect is much stronger in the ocean water than in the solid crust so the water bulges are higher. And because the Earth rotates much faster than the Moon moves in its orbit, the bulges move around the Earth about once a day giving two high tides per day.
Images, information and videos courtesy of NASA.