The Galilean moons

Saturday, January 18th 2014

Jupiter was at its closest approach to Earth on January 5th, so during my shift I took a photo of it each night with a 400mm lens. With that, I could see its four largest moons, Io, Europa, Ganymede and Callisto. They orbit the planet in roughly 2, 4, 8 and 16 days, so over the course of my 11 day shift I could see them all moving around the planet. I worked out which one was which using Sky and Telescope's tool. On 15th January the Moon was very close to Jupiter, which is why the sky is murky grey on that day instead of the nice black the other times.

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