The Moon
The Moon is Earth’s only natural satellite—a rocky, cratered body about one‑quarter the diameter of Earth, orbiting at an average distance of approximately 384,400 km. It influences tides, stabilizes Earth’s axial tilt, and was formed about 4.5 billion years ago following a collision between Earth and a Mars-sized object.
Source: science.nasa.gov
APODs including "The Moon"
Lunar Close-Up
12/02/1999
Late last month, NASA's Lunar Prospector spacecraft moved in for a closer look at the Moon. Now entering an extended mission phase, controllers have reduced the altitude of this polar lunar orbiter from 100 kilometers to about 30 kilometers (18 miles). Having mapped global properties and recorded evidence for water-ice at the lunar poles, the lower orbit allows Prospector's instruments to gather valuable confirming data at higher resolutions. The new orbit is not without some risk, though, and maneuvers are required every 28 days to maintain it. Should the maneuvers fail to be performed, the spacecraft would impact the surface only two days later. This lunar close-up was recorded by the European Southern Observatory's new WFI camera. It shows dramatic shadows and contrasting terrain near the prominent Gassendi crater at the northern edge of the Moon's Mare Humorum.