|Alternative names||Great Forty-Foot telescope |
|Location(s)|| Slough, United Kingdom |
|Coordinates|| Coordinates: |
|First light||19 February 1787 |
|Telescope style|| Altazimuth mount |
|Diameter||48 in (1.2 m) |
|Focal length||40 ft (12 m) |
William Herschel's 40-foot telescope, also known as the Great Forty-Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a 48-inch (120 cm) diameter primary mirror with a 40-foot-long (12 m) focal length (hence its name "Forty-Foot"). It was the largest telescope in the world for 50 years. It may have been used to discover Enceladus and Mimas, the 6th and 7th moons of Saturn. It was dismantled in 1840; today the original mirror and a 10-foot (3.0 m) section of the tube remain.
Frederick William Herschel, was a German-born British astronomer, composer and brother of fellow astronomer Caroline Herschel, with whom he worked. Born in the Electorate of Hanover, Herschel followed his father into the Military Band of Hanover, before migrating to Great Britain in 1757 at the age of nineteen.
A reflecting telescope is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century, by Isaac Newton, as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Reflecting telescopes come in many design variations and may employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a "catoptric" telescope.
Observatory House was an observatory in Slough, England. It was built, run and used by the astronomer William Herschel, and his sister Caroline. The famous '40-foot telescope' - at that time the largest in the world - was housed there in the late 18th century and early 19th century.
The telescope was constructed by Sir William Herschel, with the assistance of his sister Caroline Herschel, between 1785 and 1789 in Slough, with components made in Clay Hall near Windsor. The 40 ft (12 m) tube was made of iron. The telescope was mounted on a fully rotatable alt-azimuth mount. It was paid for by King George III, who granted £4,000 for it to be made. During construction, whilst the telescope tube lay on the ground, the King as well as the Archbishop of Canterbury visited the telescope. Just prior to them entering the open mouth of the tube, the King commented "Come, my Lord Bishop, I will show you the way to Heaven!"
Caroline Lucretia Herschel was a German astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigollet, which bears her name. She was the younger sister of astronomer William Herschel, with whom she worked throughout her career.
Slough is a large town in Berkshire, England, on the western fringes of the Greater London Urban Area, 20 miles (32 km) west of Charing Cross, central London, 2 miles (3 km) north of Windsor, 5 miles (8 km) east of Maidenhead, 11 miles (18 km) south-east of High Wycombe and 17 miles (27 km) north-east of the county town of Reading. It is between the Thames Valley and London and at the intersection of the M4, M40 and M25 motorways.
Clay Hall is a mid-twentieth century women's dormitory located on the campus of Northern Oklahoma College in Enid, Oklahoma that has been listed on the National Register of Historic Places since 2012. Architect Roy W. Shaw designed it for Phillips University in 1941. The building was named after Robert Henry Clay, the husband of Sadie Clay, who had given a $25,000 donation to the project. A cornerstone ceremony was held on October 9, 1941. Mefford construction had completed the exterior by 1942, and the interior was completed in 1946, having been delayed by the onset of World War II. The dormitory cost $175,000 to build, and the University held a dedication ceremony on October 11, 1946. In 1951 and 1959, a north and a south wing were added to the building in order to accommodate an expanding student population. These additional wings increased Clay Hall's residential space from 150 women to 258, and its building size to 59,000 square feet. Phillips University's enrollment peaked in the 1970s, and the dormitory closed briefly in 1985, was reopened in 1986, and then permanently shut down in 1987. Clay Hall is the oldest dormitory on the campus. Its predecessor, Athenian Hall, was demolished in 1952, and a men's dormitory, Earl Butts Hall, was completed in 1955.
Two 48-inch (120 cm) concave metal mirrors were made for the telescope, each with a focal ratio of f/10. The first was cast in a London foundry on 31 October 1785, and was made of speculum (an alloy of mostly copper and tin) with arsenic to improve the finish. It weighed 1023 lb after being cast, but it was found to be 0.9 inches thinner at the centre than at the edge (where it was around 2 inches thick). Over a year was spent grinding and polishing the mirror; however, Herschel found it to be "much too thin to keep its figure when put into the telescope" (despite weighing half a ton). A second mirror with twice the thickness of the original was cast a few years later, and this was used rather than the original. However, this required more frequent polishing due to the fast tarnishing nature of the metal, and the original mirror was used when the second was being polished. The mirrors remained the largest in the world until 1845.
A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex or concave. Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images.
Speculum metal is a mixture of around two-thirds copper and one-third tin making a white brittle alloy that can be polished to make a highly reflective surface. It was used historically to make different kinds of mirrors from personal grooming aids to reflecting telescope optical mirrors until it was replaced by more modern materials.
Copper is a chemical element with symbol Cu and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orange color. Copper is used as a conductor of heat and electricity, as a building material, and as a constituent of various metal alloys, such as sterling silver used in jewelry, cupronickel used to make marine hardware and coins, and constantan used in strain gauges and thermocouples for temperature measurement.
Herschel eliminated the small diagonal mirror of a standard newtonian reflector from his design and instead tilted his primary mirror so he could view the formed image when he stood in an observing cage directly in front of the telescope. This saved on the severe light loss the image would suffer if he had used a speculum metal diagonal mirror. This design has come to be called a Herschelian telescope.
A primary mirror is the principal light-gathering surface of a reflecting telescope.
The telescope was located on the grounds of Observatory House, Herschel's house in Slough, between 1789 and 1840.The first observation with the telescope was on 19 February 1787, when Herschel pointed the then-incomplete telescope towards the Orion nebula, which he observed by crawling into the telescope and using a hand-held eyepiece: "The apparatus for the 40-foot telescope was by this time so far completed that I could put the mirror into the tube and direct it to a celestial object; but having no eye-glass fixed, not being acquainted with the focal length which was to be tried, I went into the tube, and laying down near the mouth of it I held the eye-glass in my hand, and soon found the place of the focus. The object I viewed was the nebula in the belt of Orion, and I found the figure of the mirror, though far from perfect, better than I had expected. It showed four small stars in the nebula and many more. The nebula was extremely bright."
In astronomy, first light is the first use of a telescope to take an astronomical image after it has been constructed. This is often not the first viewing using the telescope; optical tests will probably have been performed in daylight to adjust the components. The first light image is normally of little scientific interest and is of poor quality, since the various telescope elements are yet to be adjusted for optimum efficiency. Despite this, a first light is always a moment of great excitement, both for the people who design and build the telescope and for the astronomical community, who may have anticipated the moment for many years while the telescope was under construction. A well-known and spectacular astronomical object is usually chosen as a subject.
An eyepiece, or ocular lens, is a type of lens that is attached to a variety of optical devices such as telescopes and microscopes. It is so named because it is usually the lens that is closest to the eye when someone looks through the device. The objective lens or mirror collects light and brings it to focus creating an image. The eyepiece is placed near the focal point of the objective to magnify this image. The amount of magnification depends on the focal length of the eyepiece.
The one achievement of the telescope was to discover Enceladus and Mimas, the 6th and 7th moons of Saturn, although this is not certain, as Herschel used other telescopes at the same time.Herschel described the view of Sirius through the telescope: "... the appearance of Sirius announced itself, ... and came on by degrees, increasing in brightness, till this brilliant star at last entered the field of view of the telescope, with all the splendour of the rising sun, and forced me to take the eye from that beautiful sight."
Mimas, also designated Saturn I, is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology.
The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury. Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own. Seven Saturnian moons are large enough to be ellipsoidal in shape, yet only two of those, Titan and Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes found nowhere else in the solar system; and Enceladus since its chemical composition is similar to that of comets. In particular, Enceladus emits jets of gas and dust, which could indicate the presence of liquid water under its south pole region, and may have a global ocean below its surface.
Sirius is a binary star and the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The system has the Bayer designation α (Alpha) Canis Majoris. The binary system consists of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, designated Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.
As part of the funding deal with the telescope, Caroline Herschel was granted a pension of £50 per year to be William's assistant. As a result, she was the first woman in England to be paid to carry out astronomy.
The telescope was a local tourist attraction,visited by rich and famous people on their way to the nearby Windsor Castle to visit the King, and was featured on Ordnance Survey maps. It was the largest telescope in the world for 50 years. It was called the "40-foot telescope" as at the time telescopes were referred to by the length of their tube rather than the diameter of the mirror.
Due to problems with the mirrors and because the telescope was unwieldy, the telescope did not prove to be a substantial improvement over smaller telescopes.The weather was rarely suitable for the telescope, and most objects observed by Herschel were also visible in his smaller telescopes. The final observation made by the telescope was in 1815.
The telescope was featured in Herschel's coat of arms: "Argent on a mount vert a representation of the forty-feet reflecting telescope with its apparatus proper; a chief azure thereon the astronomical symbol of Uranus or Georgium Sidus irradiated Or."
The telescope's frame was dismantled at the end of 1839 by William Herschel's son, John Herschel,on his return from carrying out observations in South Africa. It was dismantled as it was feared that the frame might collapse due to rot, and John feared for the safety of his young children. A small ceremony was conducted to commemorate its dismantling.
The tube was left lying horizontally in the garden, supported by stone blocks at either end, where it was crushed in 1867 by a falling tree. 10-foot (3.0 m) length of the mirror end, which is 3,048 by 1,465 mm (120" x 57.7"). This was still located in the garden of Observatory House in 1955, but was subsequently moved and is now located in the Herschel Collection of the National Maritime Museum, in the Royal Observatory, Greenwich, London.The remaining piece is a
The first mirror was last polished in 1797, and was subsequently stored away and lost. When John Herschel moved from Observatory House to Hawkhurst in 1840, a number of items (including the 40-foot telescope) were left behind. In an inventory written at the time, he recorded "In the Observatory, beneath stair, one 40-foot mirror, with case and cover." A workman later reported that only a light metal cover of a 4-foot mirror was present, rather than the mirror itself. The mirror was rediscovered on 2 February 1927: "All that could be seen on a casual inspection was a somewhat rusty iron ring, about 4 feet in diameter and 5 inches thick ... covered in front with a close-fitting lid of thin metal. The iron ring, which was not unlike the tyre of a cart-wheel, was obviously the cell of a large mirror and was quite separate from the tin cover. On removing the latter, which was provided with six handles, the mirror itself was at once seen, occupying the front portion of the cell, close under the cover."
On 4 March 1927 the mirror was moved to the Cottage library, and was once more polished some 130 years after the mirror was last properly polished.The original mirror now resides in the Science Museum, London. The second mirror was left in place in the telescope when it was dismantled, but was removed when the tube was crushed. In 1871 it was moved into the hall of Observatory House.
A scale model of the telescope, as well as an early photo of it that is framed in wood from the telescope, is on display at the Herschel Museum of Astronomy in Bath.
The 40-foot (12 m) telescope was surpassed in 1845 as the largest ever built by Lord Rosse's great 72-inch (1.8 m) reflecting telescope. The image of the 40-foot telescope remains as one of the great icons of astronomy.
|Wikimedia Commons has media related to 40-foot telescope .|
The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 1,740-metre (5,710-foot) peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles.
The earliest known telescope appeared in 1608 in the Netherlands when an eyeglass maker named Hans Lippershey tried to obtain a patent on one. Although Lippershey did not receive his patent, news of the new invention soon spread across Europe. The design of these early refracting telescopes consisted of a convex objective lens and a concave eyepiece. Galileo improved on this design the following year and applied it to astronomy. In 1611, Johannes Kepler described how a far more useful telescope could be made with a convex objective lens and a convex eyepiece lens and by 1655 astronomers such as Christiaan Huygens were building powerful but unwieldy Keplerian telescopes with compound eyepieces.
William Lassell, was an English merchant and astronomer. He is remembered for his improvements to the reflecting telescope and his ensuing discoveries of four planetary satellites.
William Parsons, 3rd Earl of Rosse HFRSE, was an Anglo-Irish astronomer who had several telescopes built. His 72-inch telescope, built in 1845 and colloquially known as the "Leviathan of Parsonstown", was the world's largest telescope, in terms of aperture size, until the early 20th century. From April 1807 until February 1841, he was styled as Baron Oxmantown.
The Hale Telescope is a 200-inch (5.1 m), f/3.3 reflecting telescope at the Palomar Observatory in California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, design, and construction of the observatory, but with the project ending up taking 20 years he did not live to see its commissioning. The Hale was groundbreaking for its time, with double the diameter of the second-largest telescope, and pioneered many new technologies in telescope mount design and in the design and fabrication of its large aluminum coated "honeycomb" low thermal expansion Pyrex mirror. It was completed in 1948 and is still in active use.
Leviathan of Parsonstown, or Rosse six-foot telescope, is a historic reflecting telescope of 72 in (1.8 m) aperture, which was the largest telescope in the world from 1845 until the construction of the 100-inch (2.5 m) Hooker Telescope in California in 1917. The Rosse six-foot telescope was built by William Parsons, 3rd Earl of Rosse on his estate, Birr Castle, at Parsonstown.
Stull Observatory is an astronomical observatory owned and operated by Alfred University. Named after Dr. John Stull, who helped establish the observatory in 1966, it is located in Alfred, New York (USA). It is notable for housing seven independently housed telescopes ranging in size from 8 to 32 inches. The largest, the Austin-Fellows 32 inch Newtonian Reflector is tied with the Vassar College Class of 1951 Observatory for the rank of second largest optical telescope in New York state after the 40 inch telescope at SUNY Oneonta College Observatory. Telescopes at the observatory are regularly opened to the public. The observatory is also used for those pursuing a minor in astronomy or a concentration in astrophysics.
Sir Howard Grubb, Parsons and Co. Ltd. was a telescope manufacturer, more commonly known as Grubb Parsons. It was based in Newcastle upon Tyne.
The Crossley telescope is a 36-inch (910 mm) reflecting telescope located at Lick Observatory in the U.S. state of California.
The first reflecting telescope built by Sir Isaac Newton in 1668 is a landmark in the history of telescopes, being the first known successful reflecting telescope. It was the prototype for a design that later came to be called a newtonian telescope.
Great refractor refers to a large telescope with a lens, usually the largest refractor at an observatory with an equatorial mount. The preeminence and success of this style in observational astronomy was an era in telescope use in the 19th and early 20th century. Great refractors were large refracting telescopes using achromatic lenses. They were often the largest in the world, or largest in a region. Despite typical designs having smaller apertures than reflectors, Great refractors offered a number of advantages and were favored for astronomy.
The Great Melbourne Telescope was built by Thomas Grubb in Dublin, Ireland in 1868, and installed at the Melbourne Observatory in Melbourne, Australia in 1869. In 1945 that Observatory closed and the telescope was sold and moved to the Mount Stromlo Observatory near Canberra. It was rebuilt in the late 1950s. In 2003 the telescope was practically destroyed in a severe bushfire, but a project to restore it to working condition is under way.