Sliver

The Moon is Earth’s only natural satellite, with a mean radius of 1,737.4 km and an average distance of about 384,400 km. It is roughly 4.5 billion years old and is locked in synchronous rotation, meaning its rotation period matches its 27.3-day orbit around Earth and the same hemisphere usually faces us. Its angular diameter varies from about 29.3 to 34.1 arcminutes as its distance changes.

At 4% illumination, this is a very young waxing crescent. The terminator — the line dividing the lit and unlit halves — lies close to the Moon’s eastern near-side limb, where low solar illumination strongly emphasizes relief. Terrain visible at such phases commonly includes rugged highlands and limbward features such as Mare Crisium, a basalt-filled impact basin about 555 km across, along with nearby craters including Cleomedes, Langrenus, and Petavius depending on libration.

The Moon’s dark maria are ancient plains of solidified basalt, while the brighter highlands are older, heavily cratered anorthositic crust. With no substantial atmosphere, lunar surface temperatures vary widely, from roughly 100 K at night to nearly 390 K in direct sunlight near the equator.