The Moon
The Moon is the only natural satellite of Earth, orbiting at an average distance of around 378,000 kilometers and completing one orbit every 29.5 days. With a diameter of 3,474 km, it is roughly one-quarter Earth's size. The Moon matters greatly because its gravity drives Earth's tides, which influence ocean currents and ecosystems. It is also the brightest object in Earth's night sky and has been crucial to human knowledge, mythology, and timekeeping throughout history. The Moon formed about 4.35 billion years ago from material ejected when a Mars-sized body collided with the early Earth. It remains the only celestial body beyond Earth that humans have visited, with twelve people landing on its surface during Apollo missions.
Sources
- en.wikipedia.org: “The Moon is the only natural satellite of Earth. It orbits Earth in an elliptical path, at a distance that varies over the year, averaging around 378,000 kilometers (235,000 mi).”
- en.wikipedia.org: “It completes an orbit (lunar month) in relation to Earth and the Sun (synodically) every 29.5 days.”
- en.wikipedia.org: “Its mass is 1.2% that of the Earth, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of Earth's (about as wide as the contiguous United States).”
- en.wikipedia.org: “The resulting tidal forces are the main driver of Earth's tides, and have pulled the Moon to always face Earth with the same near side.”
- en.wikipedia.org: “The Moon is the brightest celestial object in Earth's night sky because of its large apparent size, while the reflectance (albedo) of its surface is comparable to that of asphalt.”
- en.wikipedia.org: “Studies based on isotopic dating crystallization of the lunar magma ocean suggested that the Moon formed 4.35 billion years ago, late in the history of the Solar System.”
- en.wikipedia.org: “The Moon has been an important source of inspiration and knowledge in human history, having been crucial to cosmography, mythology, religion, art, time keeping, natural science and spaceflight.”
- en.wikipedia.org: “making the Moon the only celestial body beyond Earth that humans have visited.”
- en.wikipedia.org: “By 1972, six Apollo missions had landed twelve people on the Moon and stayed up to three days.”