1986 - Cruithne discovered.

Sonia Keys

Sometimes referred to as Earth's second moon, the 5 km wide asteroid 3753 Cruithne was discovered by Duncan Waldron, a Scottish ameteur astronomer. It orbits the sun in an even orbital resonance with the Earth. From the Earth, the orbit looks like a horseshoe orbit that passes closest to Earth every November at a distance 30 times the distance from the Earth to the Moon.