Uranus and Ariel. Hubble Space Telescope image of the moon Ariel (white dot) orbiting its planet Uranus (blue and green). The shadow of the moon (black dot) is seen to the moon's right. This is a rare event. Because Uranus is tipped on its side, rotating with its poles parallel to the plane of its orbit around the Sun, its moons rarely pass between it and the Sun. Ariel only does so every 42 years during the equinoxes of Uranus. Ariel is 600 kilometers in diameter and takes 2.5 days to orbit Uranus at a distance of 190,000 kilometers. Uranus is 51,000 kilometers in diameter. This image was obtained in infrared light on 26 July 2006 by Hubble's Advanced Camera for Surveys instrument.