february: galilean vista

This remarkable photograph contains quite a collection of astronomical phenomena with a recurring theme. The Moon, although behind cloud, is very obvious. It is a waning crescent, but earthshine - light reflected from the Earth - has made the dark side visible. This phenomenon is known as the old moon in the new moon's arms or, as in this case, the new moon in the old moon's arms. It was Galileo who first realised what caused it.

The bright object in the opposite corner is Jupiter, and close to it are another four moons: Callisto and Europa below and Io (almost lost in Jupiter's glare) and Ganymede above. They were discovered by Galileo using an early telescope. He tracked their movements and recognised them as satellites of Jupiter, and they are known as the Galilean moons in his honour.

The open cluster of stars to the left of Jupiter is M44 (the 4^th item in Messier's catalogue of deep sky objects) also known as the Beehive Cluster. It was thought to be a nebula until Galileo again used his telescope to resolve its bright blue stars.

Image: Russell Croman.