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William Herschel Telescope

Frederick William Herschel
(1738-1822)

Frederick William Herschel was born in Hanover, Germany on 15th November 1738. At the age of 14 he joined the local regimental band as an oboist, and 4 years later he visited England with his band. He emigrated to England in 1757, and earned his living as a musician, including a stint of 16 years as organist at the Octagon chapel in Bath.

During this period he became fascinated by astronomy. In 1772 he brought his sister Caroline to England; she shared his interest in astronomy and they worked closely together thereafter.

The Herschels started work constructing telescopes and grinding mirrors in 1773. The first large telescope to be constructed was a 1.8-m Gregorian reflector built in 1774.

He had for some nine years been carrying out increasingly thorough sky surveys, where his purpose was the investigation of double stars. Catalogues of double stars were published in 1782, 1785 and 1821, listing 848 stars in total. The resolving power of the Herschel telescopes revealed that the nebulae in the Messier catalogue were in fact clusters of stars. Catalogues of nebulae were published in 1802 (2,500 objects) and 1820 (5,000 objects). These subsequently formed the bulk of the New General Catalogue, published by Johan Dreyer in 1888, the nomenclature of which is still widely used.

In the course of an observation he realized that one celestial body he had observed was not a star at all, but a planet. Uranus was the first planet to be discovered since antiquity and Herschel and his sister and assistant Caroline became famous overnight. The sky survey revealed this as a disk, only 4 arcseconds in diameter. It was initially named 'Georgium Sidum' in honour of King George III. As a result of this discovery George III appointed him 'Court Astronomer' and granted pensions to brother and sister. He was elected as a Fellow of the Royal Society and grants were provided for the construction of new telescopes.

This discovery is not, however, his only claim to pre-eminence; he was a great observational astrophysicist and it is for these achievements that the Herschel Telescope is named after him. Herschel's investigations into double stars enabled him to demonstrate statistically that these were not chance pairings due to a line-of-sight effect, but were physically linked binary star systems. The determination of their orbits was the first evidence that Newton's law of gravitation was universal, and was seen to be operating outside our own Solar System. Herschel also determined the motion of the Sun through space.

Herschel vastly increased the numbers of known nebulae, from Messier's famous list of 100 to the 5000 catalogued by Caroline and him by 1820, and his view that the nebulae were greatly distant aggregations of stars, which today we call galaxies, was more than a century before his time.

Herschel pioneered the use of astronomical spectrophotometry as a diagnostic tool, using prisms and temperature measuring equipment to measure the wavelength distribution of stellar spectra.

Other work included an improved determination of the rotation period of Mars, the discovery that the Martian polar caps vary seasonally, the discovery of Titania and Oberon (satellites of Uranus) and Enceladus and Minas (satellites of Saturn).

Herschel visited Paris in 1801 and met Laplace and Napoleon Bonaparte. He was knighted in 1816. He died on 26th August 1822, and his work was continued by his only son, John Frederick William Herschel.

More information on Sir William Herschel can be found on this web page at SEDS. The Herschel Astronomical Society provides useful information on William Herschel as well.



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Last modified: 13 December 2010