| William Herschel | |
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| Born | 15 November 1738 Hanover, Brunswick-Lüneburg, Holy Roman Empire |
| Died | 25 August 1822 (aged 83) Slough, Berkshire, England |
| Nationality | German; later British |
| Fields | Astronomy and Music |
| Known for | Discovery of Uranus, discovery of infrared radiation, deep sky surveys |
| Notable awards | Copley Medal |
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Sir Frederick William Herschel,[1] KH, FRS, German: Friedrich Wilhelm Herschel (15 November 1738 – 25 August 1822) was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19. Herschel became most famous for the discovery of Uranus in addition to two of its major moons, Titania and Oberon. He also discovered two moons of Saturn and infrared radiation. Herschel is also known for the twenty-four symphonies that he composed.
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Sir William Herschel lived most of his life in Slough and is a man very much respected in the Berkshire town. He died in Slough and was also buried there. A new Bus Station was built in the centre of Slough in 2011 and the design was inspired by the infrared experiment of Sir William Herschel. He was buried under the tower of St Laurences Church, Upton, Slough. The Shopping centre in the town, 'The Observatory', also comes in memory of him.
Herschel was born in Hanover, Electorate of Hanover one of ten children of Isaak and Anna Ilse, née Moritzen, Herschel. His father was of Jewish descent[2] and an oboist in the Hannover Military Band. In 1755 the Hannoverian Guards regiment, in whose band Wilhelm and his brother Jakob were engaged as oboists, was ordered to England. At the time the crowns of Great Britain and Hannover were united under George II. As the threat of war with France loomed, the Hannoverian Guard was recalled from England to defend Hannover. After the Hannoverian guard was defeated at the Battle of Hastenbeck, Herschel's father Isaak sent his two sons to seek refuge in England in late 1757. Although his older brother Jakob had received his dismissal from the Hannoverian Guard, Wilhelm was accused of desertion,[3] (for which he was pardoned by George III in 1782).[4] Wilhelm, nineteen years old at this time, was a quick student of the English language. In England he went by the English rendition of his name, Frederick William Herschel.
He played the cello and harpsichord in addition to the oboe and later the organ. He composed numerous musical works, including 24 symphonies and many concertos, as well as some church music. Six of his symphonies are available in excellent recordings made in 2003 by the London Mozart Players, conducted by Matthias Bamert (Chandos 10048).
Herschel moved to Sunderland in 1761 when Charles Avison immediately engaged him as first violin and soloist for his Newcastle orchestra, where he played for one season. In ‘Sunderland in the County of Durham 20 April 1761’ he wrote his symphony no. 8 in C minor. He was head of the Durham Militia band 1760–61 and visited the home of Sir Ralph Milbanke at Halnaby Hall in 1760, where he wrote two symphonies, as well as giving performances himself.
After Newcastle he moved to Leeds and Halifax where he was the first organist at St John the Baptist church. He became organist of the Octagon Chapel, Bath, a fashionable chapel in a well-known spa, in which town he was also Director of Public Concerts. He was appointed as the organist in 1766 and gave his introductory concert on 1 January 1767. As the organ was still incomplete he showed off his versatility by performing his own compositions including a violin concerto, an oboe concerto and a harpsichord sonata. The organ was completed in October 1767.[5] His sister Caroline came to England in 1772 and lived with him there in New King Street. His brothers Dietrich, Alexander and Jakob (1734–1792) also appeared as musicians of Bath. In 1780, Herschel was appointed director of the Bath orchestra, with his sister often appearing as soprano soloist.
Herschel's music led him to an interest in mathematics and lenses. His interest in astronomy grew stronger after he made the acquaintance of the English Astronomer Royal Nevil Maskelyne. He started building his own reflecting telescopes and would spend up to 16 hours a day grinding and polishing the speculum metal primary mirrors.[6] He "began to look at the planets and the stars" in May, 1773 and on 1 March 1774 began an astronomical journal by noting his observations of Saturn's rings and the Great Orion Nebula (M 42).
Herschel's early observational work soon focused on the search for visually very close pairs of stars. Astronomers of the era expected that changes over time in the apparent separation and relative location of these stars would provide evidence both for the proper motion of stars and, by means of parallax shifts in their separation, for the distance of stars from the Earth (a method first suggested by Galileo Galilei).[7] From the back garden of his house in New King Street, Bath and using a 6.2-inch aperture (160 mm), 7-foot focal length (2.1 m) (f/13) Newtonian telescope "with a most capital speculum" of his own manufacture,[8] Herschel began a systematic search for these stars among "every star in the Heavens" in October, 1779 and continued listing discoveries through 1792. He soon discovered many more binary and multiple stars than expected, and compiled them with careful measurements of their relative positions in two catalogues presented to the Royal Society, London in 1782 (269 double or multiple systems) and 1784 (434 systems). A third catalogue of discoveries made after 1783 was published in 1821 (145 systems). In 1797 Herschel measured many of the systems again, and discovered changes in their relative positions that could not be attributed to the parallax caused by the Earth's orbit. He waited until 1802 (in Catalogue of 500 new Nebulae, nebulous Stars, planetary Nebulae, and Clusters of Stars; with Remarks on the Construction of the Heavens) to announce the hypothesis that the two stars might be "binary sidereal systems" orbiting under mutual gravitational attraction, a hypothesis he confirmed in 1803 in his Account of the Changes that have happened, during the last Twenty-five Years, in the relative Situation of Double-stars; with an Investigation of the Cause to which they are owing. In all, Herschel discovered over 800 confirmed[9] double or multiple star systems, almost all of them physical rather than virtual pairs. His theoretical and observational work provided the foundation for modern binary star astronomy; new catalogues adding to his work were not published until after 1820 by Friedrich Wilhelm Struve, James South and John Herschel.
In March, 1781, during his search for double stars, Herschel noticed an object appearing as a nonstellar disk.[10] Herschel originally thought it was a comet or a star. He made many more observations of it, and afterwards Russian Academician Anders Lexell computed the orbit and found it to be probably planetary.[11] Herschel determined in agreement that it must be a planet beyond the orbit of Saturn.[12] He called the new planet the 'Georgian star' (Georgium sidus) after King George III, which also brought him favour; the name didn't stick, however. In France, where reference to the British king was to be avoided if possible, the planet was known as 'Herschel' until the name 'Uranus' was universally adopted. The same year, Herschel was awarded the Copley Medal and elected a Fellow of the Royal Society. In 1782, he was appointed "The King’s Astronomer" (not to be confused with the Astronomer Royal). He and his sister subsequently moved to Datchet (then in Buckinghamshire but now in Berkshire) on 1 August 1782. He continued his work as a telescope maker and achieved an international reputation for their manufacture, profitably selling over 60 completed reflectors to British and Continental astronomers.[13]
From 1782 to 1802, and most intensively from 1783 to 1790, Herschel conducted systematic surveys in search of "deep sky" or nonstellar objects with two 20-foot focal length (610 cm), 12-inch aperture (30 cm) and 18.7-inch aperture (47 cm) telescopes (in combination with his favoured 6 inch aperture instrument). Excluding duplicated and "lost" entries, Herschel ultimately discovered over 2400 objects defined by him as nebulae. (At that time, nebula was the generic term for any visually extended or diffuse astronomical object, including galaxies beyond the Milky Way, until galaxies were confirmed as extragalactic systems by Edwin Hubble in 1924.) Herschel published his discoveries as three catalogues: Catalogue of One Thousand New Nebulae and Clusters of Stars (1786), Catalogue of a Second Thousand New Nebulae and Clusters of Stars (1789) and the previously cited Catalogue of 500 New Nebulae ... (1802). He arranged his discoveries under eight "classes": (I) bright nebulae, (II) faint nebulae, (III) very faint nebulae, (IV) planetary nebulae, (V) very large nebulae, (VI) very compressed and rich clusters of stars, (VII) compressed clusters of small and large [faint and bright] stars, and (VIII) coarsely scattered clusters of stars. Herschel's discoveries were supplemented by those of Caroline Herschel (11 objects) and his son John Herschel (1754 objects) and published by him as General Catalogue of Nebulae and Clusters in 1864. This catalogue was later edited by John Dreyer, supplemented with discoveries by many other 19th century astronomers, and published in 1888 as the New General Catalogue (abbreviated NGC) of over 6200 deep sky objects. The NGC numbering is still the most commonly used identifying label for these celestial landmarks.
In 1783 he gave Caroline a telescope, and she began to make astronomical discoveries in her own right, particularly comets. She discovered eight comets, eleven nebulae and, at her brother's suggestion, updated and corrected Flamsteed's work detailing the position of stars. This was published as the British Catalogue of Stars. She was honoured by the Royal Astronomical Society for this work. Caroline also continued to serve as his assistant, often taking notes while he observed at the telescope.
In June 1785, owing to damp conditions, he and Caroline moved to Clay Hall in Old Windsor. In 1786, the Herschels moved to a new residence on Windsor Road in Slough. He lived the rest of his life in this residence, which came to be known as Observatory House. It is no longer standing.
On 7 May 1788, he married the widow Mary Pitt (née Baldwin) at St Laurence's Church, Upton in Slough. His sister Caroline then moved to separate lodgings, but continued to work as his assistant.
During the course of his career, he constructed more than four hundred telescopes. The largest and most famous of these was a reflecting telescope with a 491⁄2-inch-diameter (1.26 m) primary mirror and a 40-foot (12 m) focal length. Because of the poor reflectivity of the speculum mirrors of that day, Herschel eliminated the small diagonal mirror of a standard newtonian reflector from his design and tilted his primary mirror so he could view the formed image directly. This design has come to be called the Herschelian telescope. On 28 August 1789, his first night of observation using this instrument, he discovered a new moon of Saturn. A second moon followed within the first month of observation. The "40-foot telescope" proved very cumbersome, however, and most of his observations were done with a smaller 18.5-inch (47 cm) 20-foot-focal-length (6.1 m) reflector. Herschel discovered that unfilled telescope apertures can be used to obtain high angular resolution, something which became the essential basis for interferometric imaging in astronomy (in particular Aperture Masking Interferometry and hypertelescopes).
| Uranus | 13 March 1781 |
| Oberon | 11 January 1787 |
| Titania | 11 January 1787 |
| Enceladus | 28 August 1789 |
| Mimas | 17 September 1789 |
In his later career, Herschel discovered two moons of Saturn, Mimas and Enceladus; as well as two moons of Uranus, Titania and Oberon. He did not give these moons their names; they were named by his son John in 1847 and 1852, respectively, well after his death.
Recently, some evidence has been cited by Dr. Stuart Eves that Herschel might have discovered rings around Uranus.[14]
Herschel measured the axial tilt of the planet Mars and discovered that the martian ice caps, first observed by Giovanni Domenico Cassini (1666) and Christiaan Huygens (1672), changed size with the planet's seasons.
From studying the proper motion of stars, he was the first to realise 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.
He also coined the word "asteroid", meaning star-like (from the Greek asteroeides, aster "star" + -eidos "form, shape"), in 1802 (shortly after Olbers discovered the second minor planet, 2 Pallas, in late March of the same year), to describe the star-like appearance of the small moons of the giant planets and of the minor planets; the planets all show discs, by comparison. However, it was not until the 1850s that 'asteroid' became a standard term for describing certain minor planets.
As part of his attempts to determine if there was a link between solar activity and the terrestrial climate, Herschel also collected records of the price of wheat, as direct meteorological measurements were not available for a sufficient period. He theorised that the price of wheat would be linked to the harvest and hence to the weather over the year. This attempt was unsuccessful due to the lack of previous solar observations against which to compare the wheat prices, but similar techniques were used later with success.[15]
Despite his numerous important scientific discoveries, Herschel was not averse to wild speculation. In particular, he believed every planet was inhabited,[16] even the Sun: he believed that the Sun had a cool, solid surface protected from its hot atmosphere by an opaque layer of cloud, and that a race of beings adapted to their strange environment lived there and had enormous heads. He believed the creatures' heads must be exceptionally large because his calculations showed that under those conditions a normal sized head would effectively explode. The original belief of life-forms inhabiting the Sun came from the sight and movement of sunspots on the surface of the Sun.
On 11 February 1800, Herschel was testing filters for the sun so he could observe sun spots. When using a red filter he found there was a lot of heat produced. Herschel discovered infrared radiation in sunlight by passing it through a prism and holding a thermometer just beyond the red end of the visible spectrum. This thermometer was meant to be a control to measure the ambient air temperature in the room. He was shocked when it showed a higher temperature than the visible spectrum. Further experimentation led to Herschel's conclusion that there must be an invisible form of light beyond the visible spectrum.
Herschel used a microscope to establish that coral had the characteristic thin cell walls of an animal, instead of it being a plant, as many believed.[6]
William Herschel and Mary had one child, John, born at Observatory House on 7 March 1792. In 1816, William was made a Knight of the Royal Guelphic Order by the Prince Regent entitling him to the prefix 'Sir'. He helped to found the Astronomical Society of London in 1820, which in 1831 received a royal charter and became the Royal Astronomical Society. In 1813, he was elected a foreign member of the Royal Swedish Academy of Sciences.
On 25 August 1822, Herschel died at Observatory House, Windsor Road, Slough, and is buried at nearby St Laurence's Church, Upton. His son John Herschel also became a famous astronomer. One of William's brothers, Alexander Herschel, moved permanently to England, near Caroline and John. His sister Caroline returned to Hanover, Germany after the death of her brother. She died on 9 January 1848.[17]
His house at 19 New King Street in Bath, Somerset where he made many telescopes and first observed Uranus, is now home to the Herschel Museum of Astronomy.
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