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William Herschel’s Discovery of Uranus

2020_04_07_kusu-fm_image_of_uranus_-_credit_-_nasa-jpl-caltech.jpg
NASA/JPL-Caltech

For most of the history of mankind there were only five known planets. These included the planets Mercury, Venus, Mars, Jupiter, and Saturn. The sixth planet Uranus was unknown until William Herschel observed it with a homemade telescope on the 13th of March in the year 1871. It had been observed several other times previously by other astronomers but it was William Hershel that realized that it was not a fixed star as others had thought.

When Herschel first saw the planet he thought it was a comet. It looked more like a fuzzy star and not a point of light that you would expect to see through a telescope when looking at a star. As he increased the magnification it grew in size. The fact that it changed its position against the starry background from night to night convinced him that it was not a fixed star. The movement of the object could only be explained by an object located much closer to earth than a star. Herschel continued to think that he had discovered a comet, but when others learned about Herschel’s discovery they determined its orbital motion as circular and not elliptical as most comet orbits are. It was soon calculated that this object was beyond the planet Saturn and so it was realized that a new planet had been discovered.

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