october: another moon

The asteroid Cruithne, discovered in 1986 but only properly understood in 1997, has been called "Earth's second Moon". This is not really an accurate term as it does not strictly orbit the Earth, but follows a complex orbit around the Sun that is linked to that of the Earth. At magnitude 15.5 it is also extremely faint: a very challenging telescope object, and much too dim to see with the naked eye.

A better candidate in some ways is the artificial moon being built above us: the International Space Station. The 130+ ton construction curently has a maximum magnitude of about -1, and may often be seen silently slipping through the dark morning or evening sky.

Image: NASA.