Observation Of Uranus

Uranus Discovery Of Uranus

Like the classical planets, Uranus is visible to the naked eye, but it was never recognized as a planet by ancient observers because of its dimness and slow orbit.[1]

Viewing Uranus can be done using a telescope, but it must have enough power. With binoculars and at low magnification in a telescope, it will just appear ass just another star. At magnitude 5.7, Uranus is bright enough to be easily visible against the background stars. A 70-80 mm telescope at 100x-150x will start to show disk of the planet.

Sir William Herschel first observed Uranus on 13 March 1781, leading to its discovery as a planet, expanding the known boundaries of the Solar System for the first time in history and making Uranus the first planet classified as such with the aid of a telescope.

Uranus had been observed on many occasions before its recognition as a planet, but it was generally mistaken for a star. Possibly the earliest known observation was by Hipparchos, who in 128 BC might have recorded it as a star for his star catalogue that was later incorporated into Ptolemy’s Almagest.[2] The earliest definite sighting was in 1690, when John Flamsteed observed it at least six times, cataloguing it as 34 Tauri. The French astronomer Pierre Charles Le Monnier observed Uranus at least twelve times between 1750 and 1769,[3] including on four consecutive nights.

Sir William Herschel observed Uranus on 13 March 1781 from the garden of his house at 19 New King Street in Bath, Somerset, England (now the Herschel Museum of Astronomy),[4] and initially reported it (on 26 April 1781) as a comet.[5] With a telescope, Herschel “engaged in a series of observations on the parallax of the fixed stars.”[6]

Herschel recorded in his journal: “In the quartile near ζ Tauri … either [a] Nebulous star or perhaps a comet.”[7] On 17 March he noted: “I looked for the Comet or Nebulous Star and found that it is a Comet, for it has changed its place.”[8] When he presented his discovery to the Royal Society, he continued to assert that he had found a comet, but also implicitly compared it to a planet.

Herschel notified the Astronomer Royal Nevil Maskelyne of his discovery and received this flummoxed reply from him on 23 April 1781: “I don’t know what to call it. It is as likely to be a regular planet moving in an orbit nearly circular to the sun as a Comet moving in a very eccentric ellipsis. I have not yet seen any coma or tail to it.”[9]

Although Herschel continued to describe his new object as a comet, other astronomers had already begun to suspect otherwise. Finnish-Swedish astronomer Anders Johan Lexell, working in Russia, was the first to compute the orbit of the new object.[10] Its nearly circular orbit led him to a conclusion that it was a planet rather than a comet. Berlin astronomer Johann Elert Bode described Herschel’s discovery as “a moving star that can be deemed a hitherto unknown planet-like object circulating beyond the orbit of Saturn”.[11] Bode concluded that its near-circular orbit was more like a planet’s than a comet’s.[11]

The object was soon universally accepted as a new planet. By 1783, Herschel acknowledged this to Royal Society president Joseph Banks: “By the observation of the most eminent Astronomers in Europe it appears that the new star, which I had the honour of pointing out to them in March 1781, is a Primary Planet of our Solar System.”[12] In recognition of his achievement, King George III gave Herschel an annual stipend of £200 on condition that he move to Windsor so that the Royal Family could look through his telescopes.

Check out the Planetary Bodies Category for similar articles on the planets of solar system!

Sources And Further Reading

[1] = “MIRA’s Field Trips to the Stars Internet Education Program”Monterey Institute for Research in Astronomy. Archived from the original
[2] = René Bourtembourg (2013). “Was Uranus Observed by Hipparchos?”. Journal for the History of Astronomy44 (4): 377–387. Bibcode:2013JHA….44..377B. doi:10.1177/002182861304400401.
[3] = Dunkerson, Duane. “Uranus – About Saying, Finding, and Describing It”. thespaceguy.com. Archived from the original on 17 April 2003.
[4] = “Bath Preservation Trust”.
[5] = Herschel, William; Watson, Dr. (1781). “Account of a Comet, By Mr. Herschel, F. R. S.; Communicated by Dr. Watson, Jun. of Bath, F. R. S”. Philosophical Transactions of the Royal Society of London71: 492–501. Bibcode:1781RSPT…71..492H. doi:10.1098/rstl.1781.0056.
[6] = Journal of the Royal Society and Royal Astronomical Society 1, 30, quoted in Miner, p. 8.
[7] = Royal Astronomical Society MSS W.2/1.2, 23; quoted in Miner p. 8.
[8] = RAS MSS Herschel W.2/1.2, 24, quoted in Miner p. 8.
[9] = RAS MSS Herschel W1/13.M, 14 quoted in Miner p. 8.
[10] = Lexell, A. J. (1787). “Recherches sur la nouvelle Planète, découverte par M. Herschel & nommée par lui Georgium Sidus”. Nova Acta Academiae Scientiarum Imperialis Petropolitanae (1): 69–82.
[11] = Johann Elert Bode, Berliner Astronomisches Jahrbuch, p. 210, 1781, quoted in Miner, p. 11.
[12] = Dreyer, J. L. E. (1912). The Scientific Papers of Sir William Herschel1. Royal Society and Royal Astronomical Society. p. 100. ISBN 978-1-84371-022-6.

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