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Uranus. Optical image of the planet Uranus (blue- white, just to upper right of centre). It is the seventh planet from the Sun and lies approximately 3000 million kilometres from Earth. Bright enough to be seen with the naked eye, it is one of four gas giants in our Solar System. It is believed to be composed almost entirely of hydrogen and helium, having a small rocky core surrounded by frozen water, methane and ammonia. It has a system of nine rings and is orbited by at least 17 moons. (KEYSTONE/SCIENCE PHOTO LIBRARY/JOHN SANFORD)