Saturday, March 7, 2009

March 7: John Herschel

Sir John Frederick William Herschel
March 7, 1792 – May 11, 1871

Sir John Frederick William Herschel, 1st Baronet KH, FRS, was an English mathematician, astronomer, chemist, and experimental photographer/inventor, who in some years also did valuable botanical work. He was the son of astronomer Sir William Herschel and the father of 12 children.

Herschel originated the use of the Julian day system in astronomy. He named seven moons of Saturn and four moons of Uranus. He made many contributions to the science of photography, and investigated colour blindness and the chemical power of ultraviolet rays.

Herschel studied at Eton College and St John's College, Cambridge. It was during his time as an undergraduate that he became friends with Charles Babbage and George Peacock. He took up astronomy in 1816, building a reflecting telescope with a mirror 18 inches (460 mm) in diameter and with a 20-foot (6.1 m) focal length. Between 1821 and 1823 he re-examined, with James South, the double stars catalogued by his father. For this work he was presented in 1826 with the Gold Medal of the Royal Astronomical Society (which he won again in 1836), and with the Lalande Medal of the French Institute in 1825, while in 1821 the Royal Society bestowed upon him the Copley Medal for his mathematical contributions to their Transactions. Herschel was made a Knight of the Royal Guelphic Order in 1831.

Declining an offer from the Duke of Sussex that they travel to South Africa on a Navy ship, Herschel and his wife paid ₤500 for passage on the 'S.S. Mountstuart Elphinstone', a ship of 611 tons, which departed from Portsmouth on 13 November 1833. The voyage to South Africa was made in order to catalogue the stars, nebulae, and other objects of the southern skies. This was to be a completion as well as extension of the survey of the northern heavens undertaken initially by his father William Herschel. He arrived in Cape Town on 15 January 1834 and set up a private 21 ft (6.4 m) telescope at Feldhausen at Wynberg. Amongst his other observations during this time was that of the return of Comet Halley. Herschel collaborated with Thomas Maclear, the Astronomer Royal at the Cape of Good Hope, and the two families became close friends.

Herschel wrote many papers and articles, including entries on meteorology, physical geography and the telescope for the eighth edition of the Encyclopædia Britannica. He also translated The Iliad of Homer.

He proposed a correction to the Gregorian calendar, making years that are multiples of 4,000 not leap years, thus reducing the average length of the calendar year from 365.2425 days to 365.24225. Although this is closer to the mean tropical year of 365.24219 days, his proposal has never been adopted because the Gregorian calendar is based on the mean time between vernal equinoxes (currently 365.2424 days).

In 1835, the New York Sun newspaper wrote a series of satiric articles that came to be known as the Great Moon Hoax, with statements falsely attributed to Herschel about his supposed discoveries of animals living on the Moon, including batlike winged humanoids.

Herschel Island (in the Arctic Ocean, north of the Yukon Territory), Mount Herschel (in Antarctica) and the crater J. Herschel on the Moon are named in his honor.

1 comment:

  1. At the time, telescopes were described by length,not diameter as became popular in the 20th century. The 21 ft Hershel telescope rebuilt by John Hershel in South Afica was essentially similar to the favorite telescope of John's father, William Hershel. Its mirror was about 19 inches in diameter.