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Why was Uranus the first planet discovered with a telescope?

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Images obtained by Voyager 2. — Uranus Two views of the southern hemisphere of Uranus, produced from images obtained by Voyager 2 on Jan. 17, 1986. In colours visible to the unaided human eye, Uranus is a bland, nearly featureless sphere (left). In a colour-enhanced view processed to bring out low-contrast details, Uranus shows the banded cloud structure common to the four giant planets (right). From the polar perspective of Voyager at the time, the bands appear concentric around the planet's rotational axis, which is pointing nearly toward the Sun. Small ring-shaped features in the right image are artifacts arising from dust in the spacecraft's camera.

Uranus was the first planet discovered with a telescope because it is the first planet to be identified that had not been recognized in prehistoric times. While the five planets known to the ancients—Mercury, Venus, Mars, Jupiter, and Saturn—are visible to the naked eye, Uranus is significantly more distant and appears only as a faint point of light, making it difficult to distinguish from a star without optical aid.123

Although Uranus had been observed several times over the century preceding its formal discovery, those earlier observers dismissed it as a star. It was not until March 13, 1781, that the English astronomer William Herschel identified the object while conducting a systematic survey of stars. Herschel noted that the object possessed a clearly visible disk, which distinguished it from the surrounding stars. After further observation revealed its motion in a nearly circular orbit around the Sun, the scientific community concluded that the object was a planet rather than a comet or a star.1245