The seventh planet in the solar system and more than 19 times as far from the Sun as Earth, Uranus has proved inscrutable even to the planetary expedition Voyager 2, which captured these images. The planet, although sometimes visible to the naked eye, was not discovered until 1781 when amateur astronomer William Herschel saw it through a telescope he had made himself. Uranus appears distinctly planetary through Earth-based telescopes; even so, it remains an almost featureless blue-green. (The coloring is caused by methane in the planetΓÇÖs atmosphere, which absorbs red light and reflects blue-green.) In 1977 a thin Saturn- like ring was discovered by an airborne NASA observatory.
