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13 March 1781Reputable source · 2 sourcesWell documented

William Herschel Discovers Uranus and Doubles the Solar System

A working musician scanning double stars from his backyard finds the first new planet in recorded history

On the timeline · around 13 March 1781 · The Telescopic and Classical EraThe Telescopic and Classical EraWilliam Herschel Discovers Uranus and Doubles the Solar System172517501775180018251850

Quick facts

Discoverer
William Herschel
Date
13 March 1781
Location
Bath, England
Recognition
Copley Medal (Nov. 1781); Royal Society Fellowship (Dec. 1781); royal pension (1782)

What happened

On 13 March 1781, William Herschel, using a telescope he had built himself after finding a commercial Gregorian instrument's performance inadequate, discovered the planet Uranus, the first planet to be discovered in historic times. Herschel had been surveying double stars from Bath, England, when he noticed an object near Eta Geminorum that showed a visible disk rather than the point of light typical of a star; three days later he observed that it had moved, but was initially unsure whether it was a planet or a comet. Even the Astronomer Royal shared the uncertainty at first, writing that it was as likely to be a regular planet moving in an orbit nearly circular round the sun as a comet moving in a very eccentric ellipse. Herschel received the Copley Medal in November 1781 and was elected to the Royal Society that December; the discovery's fame brought him a royal pension of 200 pounds a year, letting him give up his career as a professional musician by May 1782 to become a full-time astronomer.

Why it matters

Uranus was the first planet found that had been unknown to every earlier civilization, instantly extending the known boundaries of the solar system for the first time since antiquity and proving that the ancient tally of five visible planets was not the full picture. Herschel's success with a self-built reflecting telescope also demonstrated that dedicated amateur instrument-making could produce discoveries that rivaled or exceeded the capability of state-funded observatories.

How we know

Herschel's own observing logs and correspondence documenting the discovery and the initial confusion over whether the object was a planet or comet survive, along with the contemporary reactions of the Astronomer Royal and the Royal Society, which awarded Herschel the Copley Medal within months of the discovery.

Sources

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