Frederick William Herschel ( ; ; 15 November 1738 – 25 August 1822) was a German–British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline Herschel. Born in the Electorate of Hanover, he followed his father into the military band of Hanover, before emigrating to Britain in 1757 at the age of 19.
Taking an interest in astronomy in 1766, Herschel constructed his first large telescope in 1774, after which he spent nine years carrying out sky surveys to investigate double stars. Herschel published catalogues of nebulae in 1802 (2,500 objects) and in 1820 (5,000 objects). The resolving power of the Herschel telescopes revealed that many objects called nebulae in the Messier catalogue were actually clusters of stars. On 13 March 1781 while making observations he made note of a new object in the constellation of Gemini. This would, after several weeks of verification and consultation with other astronomers, be confirmed to be a new planet, eventually given the name of Uranus. This was the first planet to be discovered since antiquity, and Herschel became famous overnight. As a result of this discovery, George III appointed him Court Astronomer. He was elected a Fellow of the Royal Society and grants were provided for the construction of new telescopes.
Herschel pioneered the use of astronomical spectrophotometry, using prisms and temperature measuring equipment to measure the wavelength distribution of stellar spectra. In the course of these investigations, Herschel discovered infrared radiation. 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 (moons of Uranus) and Enceladus and Mimas (moons of Saturn). Herschel was made a Knight of the Royal Guelphic Order in 1816. He was the first President of the Royal Astronomical Society when it was founded in 1820. He died in August 1822, and his work was continued by his only son, John Herschel.
Early life and musical activities Herschel was born in the Electorate of Hanover in Germany, then part of the Holy Roman Empire, one of ten children of Isaak Herschel and his wife, Anna Ilse Moritzen, of German Lutheran ancestry. His ancestors came from Pirna, in Saxony. Theories that they were Protestants from Bohemia have been questioned by Hamel as the surname Herschel already occurred a century earlier in the very same area in which the family lived.
Herschel's father was an oboist in the Hanover Military Band. In 1755 the Hanoverian 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 Hanover were united under King George II. As the threat of war with France loomed, the Hanoverian Guards were recalled from England to defend Hanover.
After they were 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 Hanoverian Guards, Wilhelm was accused of desertion (for which he was pardoned by George III in 1782). Wilhelm, nineteen years old at this time, was a quick student of English. In England, he anglicised his name to Frederick William Herschel.
In addition to the oboe, he played the violin and harpsichord 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 were recorded in April 2002 by the London Mozart Players, conducted by Matthias Bamert (Chandos 10048).
He was head of the Durham Militia band from 1760 to 1761. Herschel moved to Sunderland in 1761; Charles Avison engaged him as the first violin and soloist for his Newcastle orchestra, where he played for one season. In "Sunderland in the County of Durh: apprill 20th 1761" he wrote his Symphony No. 8 in C Minor. He visited the home of Sir Ralph Milbanke at Halnaby Hall near Darlington 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 (now Halifax Minster).
In 1766, Herschel became organist of the Octagon Chapel, Bath, a fashionable chapel in a well-known spa, in which city 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. On 4 October 1767, he performed on the organ for the official opening of the Octagon Chapel.
His sister Caroline arrived in England on 24 August 1772 to live with William in New King Street, Bath. The house they shared is now the location of the Herschel Museum of Astronomy. Herschel's brothers Dietrich, Alexander and Jakob also appeared as musicians of Bath. In 1780, Herschel was appointed director of the Bath orchestra, with his sister often appearing as soprano soloist.
Astronomy
Herschel's reading in natural philosophy during the 1770s not only indicates his personal interests, but also suggests an intention to be upwardly mobile, both socially and professionally. He was well-positioned to engage with eighteenth-century "philosophical gentlemen" or philomaths, of wide-ranging logical and practical tastes.
Herschel's intellectual curiosity and interest in music eventually led him to astronomy, making his first recorded observation in 1766. After reading Robert Smith's Harmonics, or the Philosophy of Musical Sounds (1749), he took up Smith's A Compleat System of Opticks (1738), which described techniques of telescope construction. He also read James Ferguson's Astronomy explained upon Sir Isaac Newton's principles and made easy to those who have not studied mathematics (1756) and William Emerson's The elements of trigonometry (1749), The elements of optics (1768) and The principles of mechanics (1754).
Herschel took lessons from a local mirror-builder and having obtained both tools and a level of expertise, started building his own reflecting telescopes. He would spend up to 16 hours a day grinding and polishing the speculum metal primary mirrors. He relied on the assistance of other family members, particularly his sister Caroline and his brother Alexander, a skilled mechanical craftsperson.
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 (M42). The English Astronomer Royal, Nevil Maskelyne, visited the Herschels while they were at Walcot (which they left on 29 September 1777). By 1779, Herschel had also made the acquaintance of Sir William Watson, who invited him to join the Bath Philosophical Society. Herschel became an active member, and through Watson would greatly enlarge his circle of contacts. A few years later, in 1785, Herschel was elected an international member of the American Philosophical Society in Philadelphia.
Double stars Herschel's early observational work soon focused on the search for pairs of stars that were very close together visually. Astronomers of the era expected that changes over time in the apparent separation and relative location of these stars would provide evidence for both the proper motion of stars and, by means of parallax shifts in their separation, for the distance of stars from the Earth. The latter was a method first suggested by Galileo Galilei. From the back garden of his house in New King Street, Bath, and using a , (f/13) Newtonian telescope "with a most capital speculum" of his own manufacture, in October 1779, Herschel began a systematic search for such stars among "every star in the Heavens", with new discoveries listed 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 in 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).
The Rev. John Michell of Thornhill published work in 1767 on the distribution of double stars, and in 1783 on "dark stars", that may have influenced Herschel. After Michell's death in 1793, Herschel bought a ten-foot-long, 30-inch reflecting telescope from Michell's estate.
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 were "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 confirmedWilliam Herschel's Double Star Catalog. Handprint.com (5 January 2011). Retrieved on 5 June 2011. double or multiple star systems, almost all of them physical rather than optical 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.
Uranus
In March 1781, during his search for double stars, Herschel noticed an object appearing as a disk. Herschel originally thought it was a comet or a stellar disc, which he believed he might actually resolve. He reported the sighting to Nevil Maskelyne the Astronomer Royal. He made many more observations of it, and afterwards Finnish-Swedish astronomer Anders Lexell computed the orbit and found it to be probably planetary.
Herschel agreed, determining that it must be a planet beyond the orbit of Saturn.Astronomical League National – Herschel Club – Friedrich Wilhelm Herschel. Astroleague.org. Retrieved on 5 June 2011. He called the new planet the "Georgian star" (Georgium sidus) after King George III, which also brought him favour; the name did not stick. 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).
On 1 August 1782 Herschel and his sister Caroline moved to Datchet (then in Buckinghamshire but now in Berkshire). There, he continued his work as an astronomer and telescope maker. He achieved an international reputation for their manufacture, profitably selling over 60 completed reflectors to British and Continental astronomers.
Deep sky surveys
From 1782 to 1802, and most intensively from 1783 to 1790, Herschel conducted systematic surveys in search of "deep-sky" or non-stellar objects with two , telescopes (in combination with his favoured 6-inch-aperture instrument). Excluding duplicated and "lost" entries, Herschel ultimately discovered over 2,400 objects defined by him as nebulae. (At that time, nebula was the generic term for any visually diffuse astronomical object, including galaxies beyond the Milky Way, until galaxies were confirmed as extragalactic systems by Edwin Hubble in 1924.)