Compilation album

A compilation album comprises tracks which are compiled from other recordings, usually previously released, but sometimes unreleased. The tracks may be from one or several performers; if from several performers there may be a theme, topic or genre which links the tracks. When the tracks are by the same recording artist, the album may be referred to as a retrospective album. Compilation albums may employ traditional product bundling strategies.

Common types

Common types of compilation include:

MusicBrainz

MusicBrainz is a project that aims to create an open content music database. Similar to the freedb project, it was founded in response to the restrictions placed on the CDDB. However, MusicBrainz has expanded its goals to reach beyond a compact disc metadata storehouse to become a structured open online database for music.

MusicBrainz captures information about artists, their recorded works, and the relationships between them. Recorded works entries capture at a minimum the album title, track titles, and the length of each track. These entries are maintained by volunteer editors who follow community written style guidelines. Recorded works can also store information about the release date and country, the CD ID, cover art, acoustic fingerprint, free-form annotation text and other metadata. As of 25 October 2015, MusicBrainz contained information about roughly one million artists, 1.5 million releases, and 15 million recordings.

End-users can use software that communicates with MusicBrainz to add metadata tags to their digital media files, such as MP3, Ogg Vorbis or AAC.

Moon landing

A Moon landing is the arrival of a spacecraft on the surface of the Moon. This includes both manned and unmanned (robotic) missions. The first human-made object to reach the surface of the Moon was the Soviet Union's Luna 2 mission, on 13 September 1959.

The United States' Apollo 11 was the first manned mission to land on the Moon, on 20 July 1969. There have been six manned U.S. landings (between 1969 and 1972) and numerous unmanned landings, with no soft landings happening from 22 August 1976 until 14 December 2013.

To date, the United States is the only country to have successfully conducted manned missions to the Moon, with the last departing the lunar surface in December, 1972.

Unmanned landings

After the unsuccessful attempt by the Luna 1 to land on the moon in 1959, the Soviet Union performed the first hard (unpowered) moon landing later that same year with the Luna 2 spacecraft, a feat the U.S. duplicated in 1962 with Ranger 4. Since then, twelve Soviet and U.S. spacecraft have used braking rockets to make soft landings and perform scientific operations on the lunar surface, between 1966 and 1976. In 1966 the USSR accomplished the first soft landings and took the first pictures from the lunar surface during the Luna 9 and Luna 13 missions. The U.S. followed with five unmanned Surveyor soft landings.