Jordmåne

Jordmåne, the Norwegian term for Earth's Moon, is Earth's natural satellite. It orbits about 384,400 kilometers from Earth and completes a sidereal month in 27.3 days; its phases repeat roughly every 29.5 days. The Moon is tidally locked, presenting the same face to Earth.

Diameter 3,474 kilometers; mass about 7.35×10^22 kilograms. It has no substantial atmosphere, only a very thin exosphere. The surface consists of heavily cratered highlands and basaltic maria formed by ancient volcanism. The interior is differentiated with a small iron-rich core.

Formation is best explained by the giant-impact hypothesis: a Mars-sized body collided with early Earth around 4.5 billion years ago, ejecting material that formed the Moon. Isotopic similarities between Earth and lunar rocks support this scenario.

Geologic features include craters, rilles, and mare basins. The far side is more heavily cratered than the near side due to crustal differences. The Moon lacks a substantial atmosphere and currently shows no global magnetic field, though some evidence of ancient magnetism has been proposed.

Exploration began with NASA's Apollo 11 in 1969, when humans first walked on the surface. Twelve astronauts conducted walks and collected samples through 1972. Robotic missions have mapped the surface and detected water ice in permanently shadowed polar craters, informing plans for future missions.

The jordmåne influences Earth's tides and, over long timescales, stabilizes its axial tilt. It remains a primary target for studies of planetary formation, early solar-system history, and future space exploration.