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| Space on Mar 13, 2015

This date in science: Uranus discovered, completely by accident

William Herschel noticed while surveying stars that one object moved apart from the star background. It was the first planet discovered since ancient times.

March 13, 1781. The 7th planet – Uranus – was discovered on this date, completely by accident. British astronomer William Herschel was performing a survey of all the stars that were of magnitude 8 – in other words, too faint to see with the eye – or brighter. That’s when he noticed an object that moved in front of the star background over time, clearly demonstrating it was closer to us than the distant stars. At first he thought he had found a comet, but later realized this object was a new planet in orbit around our sun – the first discovered since ancient times.

Later, it turned out, astronomers learned they had observed Uranus as far back as 1690. But it was Herschel who first realized the true nature of this distant light in our sky.

William Herschel's famous 40-foot telescope,  constructed between 1785 and 1789 at Observatory House in Slough, England. It was the largest telescope in the world for 50 years.   Image via Wikimedia Commons.

William Herschel’s famous 40-foot telescope, constructed between 1785 and 1789 at Observatory House in Slough, England. It was the largest telescope in the world for 50 years. Image via Wikimedia Commons.

Herschel proposed to name the object Georgium Sidus, after King George III, but those outside of Britain weren’t pleased with the idea. Instead, on the suggestion of astronomer Johann Elert Bode, astronomers decided to follow the convention of naming planets for the ancient gods. Uranus – an ancient sky god, and one of the earliest gods in Greek mythology – was sometimes called Father Sky and was considered to be the son and husband of Gaia, or Mother Earth.

King George III was still pleased, however. As a result of Herschel’s discovery, the king knighted him and appointed him to the position of court astronomer. The pension attached let Herschel quit his day job as a musician and focus his full attention on observing the heavens. He went on to discover several moons around other gas giant planets. He also compiled a catalog of 2,500 celestial objects that’s still in use today.

Voyager 2 gave us our first close-up image of the planet Uranus in 1986.  Its images showed a featureless gas giant world.

Voyager 2 gave us our first close-up image of the planet Uranus in 1986. Its images showed a featureless gas giant world.

Voyager 2 image showing Uranus in true and false color. Image via NASA

In 1977, astronomers using the Kuiper Airborne Observatory made another serendipitous discovery – of rings around the planet Uranus. That discovery made Uranus the second known ringed planet in our solar system.

The closest we humans have come to Uranus was in 1986, when the Voyager 2 spacecraft swung by the planet. At its closest, the spacecraft came within 81,500 kilometers (50,600 miles) of Uranus’s cloudtops on Jan. 24, 1986. Voyager 2 radioed thousands of images and voluminous amounts of other scientific data on the planet, its moons, rings, atmosphere, interior and the magnetic environment surrounding Uranus.

Today, Uranus is known to possess a complicated ring system (although nowhere near as complicated as that encircling Saturn).  This schematic of the Uranian rings is from Wikimedia Commons.

Today, Uranus is known to possess a complicated ring system (although nowhere near as complicated as that encircling Saturn). This schematic of the Uranian rings is from Wikimedia Commons.

Bottom line: British astronomer William Herschel discovered the planet Uranus – first planet to be discovered since ancient times – on March 13, 1781.