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Today in science: Discovery of Uranus

It was the first planet found since ancient times. William Herschel noticed it in 1781 during a routine survey of the stars.

Pale blue Uranus as seen by Voyager 2 in 1986. Voyager 2 is the only spacecraft ever to have glimpsed Uranus up close. Image via NASA.

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 stars of at least magnitude 8 – from slightly too faint to see with the eye, in other words. That’s when he noticed a very faint object – only barely within the limit for viewing with the eye – that that moved in front of the fixed stars. This movement clearly demonstrated it was closer to us than the stars. At first he thought he had found a comet. Later, he and others realized it was a new planet in orbit around our sun, the first new planet discovered since ancient times.

Astronomers later learned they had observed Uranus as far back as 1690. They’d just never really noticed it before. 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 (12-meter) 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 pleased, whatever the name. 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.

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.

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.

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

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

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