3753 Cruithne ( /ˈkrɪnjə/, from Old Irish ; Modern or ) is an asteroid in orbit around the Sun in 1:1 orbital resonance with the Earth. It is a minor planet that orbits the Sun in a horseshoe orbit relative to Earth. It has been incorrectly called "Earth's second moon", but it is a quasi-satellite, not a moon. Cruithne does not orbit Earth, and at times it is on the other side of the Sun. Its orbit takes it inwards towards the orbit of Mercury, and outside the orbit of Mars. Cruithne orbits the Sun in about 1 year, but it takes 770 years for the series to complete a horseshoe-shaped movement, with the Earth in the gap of the horseshoe.
The name Cruithne is from Old Irish, the Celtic term for the Picts, as well as the name of a people of eastern Ulster.
Read more about 3753 Cruithne: Discovery, Dimensions and Orbit, Similar Minor Planets, Cruithne in Popular Culture