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Object: Common Name: Object Type: Constellation: Discoverer:   Catalogue Identification:   Messier:   NGC:   IC:   Caldwell:   Herschel:   X:   Features:    Bright 7th magnitude star enveloped in purple-blue coloured nebulosity. Long exposure colour photographs of NGC 7023 reveal why it is named the Iris Nebula. It bears an uncanny resemblance to the flower and in particular the ‘Dutch Blue’ Iris.   NGC7023/C4. Cepheus   Discovery: William Herschel discovered NGC 7023 on the 18th October 1794. He described it as: “A star of 7th magnitude. Very much affected by nebulosity, which more than fills the field. It seems to extend to at least a degree all around; fainter stars, such as 9th or 10th magnitude, of which there are many, are perfectly free from this appearance (H IV-74)."         Description: The Iris Nebula, also known as NGC 7023 and Caldwell 4, is a bright reflection nebula in the constellation of Cepheus. There has been much confusion over the exact nature of NGC 7023. Some sources list NGC 7023 as an open cluster with nebulosity. This is incorrect. NGC 7023 is in fact a reflection nebula with the star cluster ‘Collinder 429 involved’. The nebula shines at magnitude 7.7 and is lit by the magnitude +6.8 star, SAO 19158. NGC 7023 and its associated nebulosity were discovered by William Herschel on the 18th October 1794. It is located near the Mira-type variable star T Cephei, and near the bright magnitude +3.23 variable star Beta Cephei (Alphirk). It lies 1,300 light-years away and is six light-years across.         Important Data:           RA:   Size (w):   Size (h):     Dec:   Distance:   Magnitude:         Composition: The bright star HD 200775 shines through the nebula NGC 7023 like a beacon through a celestial fog. The illuminating star of the nebula is designated HD 200775, a 10 solar mass star centrally imbedded in a region surrounded by ambient molecular cloud material. Optically the light we see from reflection nebulae such as NGC 7023 is starlight reflected from the surface of innumerable small dust particles. Historically this was proven by showing the similarity of the spectra of the central illuminating star and its nebula. Aside from the reflected light of its central star, the microscopic dust particles also emit radiation in the infrared. We see the optical counterpart of this emission in the low level light of the dark dust clouds surrounding the bright nebula on its south and west side, respectively catalogued as L 1172 and L1174. Recent infrared studies of NGC 7023 indicate the presence of complex molecules such as polyaromatic hydrocarbons formed within the dust cloud. Images The Iris Nebula is so called because of its close resemblance to the flower of the same name. One of the earliest photographs of NGC 7023 was taken by Isaac Roberts in 1898 with a 20 inch Reflector. However it is the image taken by Charles Dillon Perrine in 1903 that shows for the very first time the tremendous amount of detail that can be seen in this magnificent reflection nebula. The series of photographs taken by James Edward Keeler and Charles Dillon Perrine during the period 1898 to 1903 using the 36” Crossley Reflector firmly established the supremacy of large silvered mirrored telescopes over the large refractor for DSO astrophotography. It was not until much later that colour photographs were taken that illustrated how close this nebula looks to the blue iris.       'The Discoverer'   Sir Frederick William Herschel, KH, FRS was a German-born English astronomer and composer who became famous for discovering the planet Uranus. He also discovered infrared radiation and made many other discoveries in astronomy. He was born Friedrich Wilhelm Herschel on the15th November 1738 in Hanover, Germany; one of ten children (of whom four died very young). Both his grandfather, who was named Abraham, and his father, Isaac Herschel (1708-1768), an oboist of the Hanover Military Band, were Jewish. However, his mother, Anna Ilse Moritzen, does not appear to have been Jewish. In 1755 the Hanoverian Guards regiment, in whose band William and his brother Jacob were engaged as oboists, was ordered to England. At the time, the crowns of England and Hannover were united under George II. This brief visit made an impression, and the next year the brothers resigned from the Guards band and moved to London. William learned English quickly and, at age nineteen, he changed his name to Frederick William Herschel. He played the cello besides the oboe and, later, the organ. During a concert in 1767, Herschel showed off his versatility by performing an oboe concerto, violin concerto and harpsichord sonata] He composed numerous musical works, including 24 symphonies and many concertos, as well as some church music. Apart from a few oboe concertos, his music is largely forgotten today. In 1761, Herschel moved to Sunderland, 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 April 20 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 organist at St John the Baptist church. He became organist of the Octagon Chapel, Bath, in which town he was also Director of Public Concerts. He was appointed as the organist in 1766 and gave his introductory concert on January 1, 1767. As the organ was still incomplete he performed his own compositions including a violin concerto, an oboe concerto and a harpsichord sonata. The organ was completed in October 1767. His sister Caroline came to England in 1772 and lived with him there in New King Street. His brothers Dietrich, Alexander and Jacob (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 thence to astronomy. This interest grew stronger after 1773, and he built some telescopes and made the acquaintance of Nevil Maskelyne. In the spring of 1781, William Herschel discovered the planet Uranus, using a homemade telescope in the back garden of his house in New King Street, in Bath. He called the new planet the 'Georgian star' 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" and 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, selling a number of them to other astronomers. In 1783 he gave Caroline a telescope and she began to make astronomical discoveries in her own right, particularly comets. She discovered eight comets, three 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 Academy 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. On 3 April 1786, William Herschel moved his family 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, having been demolished in 1963 to make way for a high-rise office building. 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. 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; rather, they were named by his son John in 1847 and 1852, respectively, well after his death. He worked on creating an extensive catalogue of nebulae. He continued to work on double stars, and was the first to discover that most double stars are not mere optical doubles as had been supposed previously, but are true binary stars, thus providing the first evidence that Newton's laws of gravitation apply outside the solar system. He also had a part in discovering the ice caps on Mars. From studying the proper motion of stars, he was the first to realize 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 from 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. Despite his numerous important scientific discoveries, Herschel was not averse to wild speculation. In particular, he believed every planet was inhabited, 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 February 11, 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 by passing sunlight 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. 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. On August 25, 1822, Herschel died at Observatory House, Windsor Road, Slough, and is buried at nearby St Laurence's Church, Upton. Coincidentally, he died in his 84th year, which is the same number of years which Uranus takes to orbit the Sun. His sister Caroline returned to Hanover, Germany after the death of her brother. She died on 9 January 1848. 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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