August 5, 2004

           Here is a photo of retrograde motion. All skywatchers are familiar with this. It happens when the Earth's orbit catches up to Mars and makes that planet appear to be moving backwards. This is an illusion against the distant background starts.
           You experience this effect looking out a car window at speed. The trees on the horizon appear to be moving forward compared to telephone poles or fence posts nearby. But why this photo is unique (and better than the rest) is Uranus. Just above Mars, you can see Uranus also in retrograde motion.