The first planet discovered with the aid of a telescope was Uranus.
Astronomer William Herschel spotted Uranus on March 13, 1781, from Bath, England, while surveying faint stars with a reflecting telescope. He initially thought the moving object was a comet, because its motion showed it was not a fixed star.
Further observations revealed that its orbit was nearly circular, indicating that it was a planet beyond Saturn. Herschel briefly proposed naming it Georgium Sidus, or “George’s Star,” after King George III. The name Uranus, suggested by Johann Elert Bode, eventually became standard.
Mercury, Venus, Mars, Jupiter, and Saturn had all been visible to ancient observers without telescopes. Uranus is therefore often described as the first planet discovered in modern times and the first found telescopically. It is the seventh planet from the Sun and is classified as an ice giant.