Illustration of Discovery of Uranus

1781 Discovery of Uranus

The book of science

Tom Sharp

William Herschel astronomy Illustration of Discovery of Uranus

Discovery of Uranus

When William Herschel was cataloging double stars in the constellation of Gemini that astronomers might determine, by parallax, their distances from Earth, he discovered an object without a tail brighter and larger than a star that appeared as a disk and grew in diameter as he zoomed in on it, which could not be a star because stars always appear as points of light. So Herschel wrote to other astronomers, and Anders Lexell calculated that its orbit was nearly circular, meaning it had to be a planet.


Herschel made more than four hundred telescopes, including a reflecting telescope with a forty-nine-and-a-half-inch-diameter mirror and a forty-foot focal length. The telescope with which he discovered Uranus he made of wood with an altazimuth mount and a reflecting mirror of speculum that he had made and polished himself. This telescope had a diameter of six and a half inches and a focal length of seven feet.


If I cannot peer with a better instrument which for a better reason I cannot find then bless my intuition which seems to be blunted before it can cut.

William Herschel was a musician and composer of church music, many concertos, and twenty-four symphonies.

Speculum is an alloy of about two-thirds copper and one-third tin. Isaac Newton made a 1.3-inch speculum mirror for the first successful reflecting telescope in 1668.

An altazimuth mount lets the telescope move on two perpendicular axes, one vertical and the other horizontal.

Herschel discovered two moons of Uranus, Titania and Oberon, and two moons of Saturn, Mimas and Enceladus. William’s son John named these moons after William died.

Although he did not discover the first asteroid, Herschel coin the term “asteroid” from the Greek for “star-shape.”

Herschel measured the tilt of Mars and discovered its ice caps. “He was the first to realize that the solar system is moving through space, and he determined the approximate direction of that movement. He also studied the structure of the Milky Way and concluded that it was in the shape of a disk.”

Herschel discovered the infrared spectrum in sunlight.

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