Because Uranus is so far away, it appears very small in the night sky, even when looking through a telescope. The first astronomers who saw the planet originally misclassified it as a star because of its dim and small appearance. In 1781, astronomer William Herschel, credited with Uranus’ discovery, realized it wasn’t a star after realizing it had moved positions after a few days. But he, like other astronomers, also misclassified it at first. Herschel originally mistook Uranus for a comet, knowing that it could not be a star due to its movement, but not expecting to find another planet.

Further investigation later revealed Uranus’ planet status, making Uranus the first planet discovered with a telescope. Technically, Uranus was the first planet ever “discovered” at all, as Mercury, Venus, Mars, Jupiter, and Saturn are all visible with the naked eye. These planets have been known as something other than stars since humanity began looking at the sky. Uranus was the first discovery of a planet that wasn’t visible to the unaided eye (via the Science Museum).

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