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The William Herschel Telescope (WHT) is a
optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
/
near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
reflecting telescope A reflecting telescope (also called a reflector) 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 alternati ...
located at the
Roque de los Muchachos Observatory Roque de los Muchachos Observatory ( es, Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated ...
on the island of
La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...
in the
Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...
, Spain. The telescope, which is named after
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
, the discoverer of the planet
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
, is part of the
Isaac Newton Group of Telescopes The Isaac Newton Group of Telescopes or ING consists of three optical telescopes: the William Herschel Telescope, the Isaac Newton Telescope, and the Jacobus Kapteyn Telescope, operated by a collaboration between the UK Science and Technology Fac ...
. It is funded by research councils from the United Kingdom, the Netherlands and Spain. At the time of construction in 1987, the WHT was the third largest single optical telescope in the world.The
BTA-6 The BTA-6 (russian: Большой Телескоп Альт-азимутальный, translit=Bolshoi Teleskop Alt-azimutalnyi, translation=Large Altazimuth Telescope) is a aperture optical telescope at the Special Astrophysical Observatory lo ...
(6.0 m) and
Hale telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, de ...
(5.1 m) were both larger; the
Multiple Mirror Telescope The MMT Observatory (MMTO) is an astronomical observatory on the site of Fred Lawrence Whipple Observatory (IAU observatory code 696). The Whipple observatory complex is located on Mount Hopkins, Arizona, US (55 km south of Tucson) in the S ...
also had a larger collecting area but did not have a single primary mirror
It is currently the second largest in Europe,The neighbouring
Gran Telescopio Canarias The Gran Telescopio Canarias (GranTeCan or GTC) is a reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain. It is the world's largest single-aperture optical telescope. Constr ...
(10.4 m) overtook the WHT in 2009 to become the largest in Europe
and was the last telescope constructed by
Grubb Parsons Sir Howard Grubb, Parsons and Co. Ltd. was a telescope manufacturer, more commonly known as Grubb Parsons. It was based in Newcastle upon Tyne, in England. They were a noted telescope maker throughout the 19th and 20th century, making telescope th ...
in their 150-year history. The WHT is equipped with a wide range of instruments operating over the
optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
and
near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
regimes. These are used by professional astronomers to conduct a wide range of astronomical research. Astronomers using the telescope discovered the first evidence for a
supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...
(
Sgr A* Sagittarius A* ( ), abbreviated Sgr A* ( ), is the supermassive black hole at the Galactic Center of the Milky Way. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, vi ...
) at the centre of the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
, and made the first
optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
observation of a
gamma-ray burst In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milli ...
. The telescope has 75% clear nights, with a median seeing of 0.7 ".


History

The WHT was first conceived in the late 1960s, when the
Anglo-Australian Telescope The Anglo-Australian Telescope (AAT) is a 3.9-metre equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia, at an altitude of a little over 1,100 m. In 2 ...
(AAT) was being designed. The British astronomical community saw the need for telescopes of comparable power in the
northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
. In particular, there was a need for optical follow-up of interesting sources in the radio surveys being conducted at the
Jodrell Bank Jodrell Bank Observatory () in Cheshire, England, hosts a number of radio telescopes as part of the Jodrell Bank Centre for Astrophysics at the University of Manchester. The observatory was established in 1945 by Bernard Lovell, a radio astron ...
and
Mullard Mullard Limited was a British manufacturer of electronic components. The Mullard Radio Valve Co. Ltd. of Southfields, London, was founded in 1920 by Captain Stanley R. Mullard, who had previously designed thermionic valves for the Admir ...
observatories (both located in the UK), which could not be done from the southern hemisphere location of the AAT. The AAT was completed in 1974, at which point the British
Science and Engineering Research Council The Science and Engineering Research Council (SERC) and its predecessor the Science Research Council (SRC) were the UK agencies in charge of publicly funded scientific and engineering research activities, including astronomy, biotechnology and bi ...
began planning for a group of three telescopes located in the northern hemisphere (now known as the
Isaac Newton Group of Telescopes The Isaac Newton Group of Telescopes or ING consists of three optical telescopes: the William Herschel Telescope, the Isaac Newton Telescope, and the Jacobus Kapteyn Telescope, operated by a collaboration between the UK Science and Technology Fac ...
, ING). The telescopes were to be a (which became the
Jacobus Kapteyn Telescope The Jacobus Kapteyn Telescope or JKT is a 1-metre optical telescope named for the Dutch astronomer Jacobus Kapteyn (1851-1922) of the Isaac Newton Group of Telescopes at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Sp ...
), the
Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984. Originally the INT was situated at He ...
which was to be moved from its existing site at
Herstmonceux Castle Herstmonceux Castle is a brick-built castle, dating from the 15th century, near Herstmonceux, East Sussex, England. It is one of the oldest significant brick buildings still standing in England. The castle was renowned for being one of the fir ...
, and a 4m class telescope, initially planned as a . A new site was chosen at an altitude of on the island of
La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...
in the
Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...
, that is now the
Roque de los Muchachos Observatory Roque de los Muchachos Observatory ( es, Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated ...
. The project was led by the Royal Greenwich Observatory (RGO), who also operated the telescopes until control passed to an independent ING when the RGO closed in 1998. By 1979 the 4 m was on the verge of being scrapped due to a ballooning budget, whilst the aperture had been reduced to . A panel known as the Tiger Team was convened to reduce the cost; a re-design cut the price-tag by 45%. Savings were primarily made by reducing the
focal length The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative foca ...
of the telescope – which allowed the use of a smaller
dome A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...
– and relocating non-essential functions outside the dome to a simpler (and thus cheaper) rectangular annexe. In the same year, the
Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984. Originally the INT was situated at He ...
was moved to
Roque de los Muchachos Observatory Roque de los Muchachos Observatory ( es, Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated ...
, becoming the first of the
Isaac Newton Group of Telescopes The Isaac Newton Group of Telescopes or ING consists of three optical telescopes: the William Herschel Telescope, the Isaac Newton Telescope, and the Jacobus Kapteyn Telescope, operated by a collaboration between the UK Science and Technology Fac ...
. In 1981 the
Nederlandse Organisatie voor Wetenschappelijk Onderzoek The Dutch Research Council (NWO, Dutch: Nederlandse Organisatie voor Wetenschappelijk Onderzoek) is the national research council of the Netherlands. NWO funds thousands of top researchers at universities and institutes and steers the course o ...
(Netherlands Organization for Scientific Research, NWO) bought a 20% stake in the project, allowing the WHT to be given the go-ahead. That year was the 200th anniversary of the discovery of Uranus by
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
, and it was decided to name the telescope in his honour. Construction of the telescope was by
Grubb Parsons Sir Howard Grubb, Parsons and Co. Ltd. was a telescope manufacturer, more commonly known as Grubb Parsons. It was based in Newcastle upon Tyne, in England. They were a noted telescope maker throughout the 19th and 20th century, making telescope th ...
, the last telescope that company produced in its 150-year history. Work began at their factory in
Newcastle upon Tyne Newcastle upon Tyne ( RP: , ), or simply Newcastle, is a city and metropolitan borough in Tyne and Wear, England. The city is located on the River Tyne's northern bank and forms the largest part of the Tyneside built-up area. Newcastle is ...
in 1983, and the telescope was shipped to
La Palma La Palma (, ), also known as ''La isla bonita'' () and officially San Miguel de La Palma, is the most north-westerly island of the Canary Islands, Spain. La Palma has an area of making it the fifth largest of the eight main Canary Islands. The ...
in 1985 (the two other telescopes of the Isaac Newton Group began operating in 1984). The WHT saw first light on 1 June 1987; it was the third largest optical telescope in the world at the time. The total cost of the telescope, including the dome and the full initial suite of instruments, was £15M (in 1984, equivalent to £M in ); within budget once inflation is taken into account.


Design


Optics

The telescope consists of a f/2.5 primary mirror made by
Owens-Illinois O-I Glass, Inc. is an American company that specializes in container glass products. It is one of the world's leading manufacturers of packaging products, holding the position of largest manufacturer of glass containers in North America, South A ...
from Cervit, a zero-expansion
glass-ceramic Glass-ceramics are polycrystalline materials produced through controlled crystallization of base glass, producing a fine uniform dispersion of crystals throughout the bulk material. Crystallization is accomplished by subjecting suitable glasses to ...
material, and ground by
Grubb Parsons Sir Howard Grubb, Parsons and Co. Ltd. was a telescope manufacturer, more commonly known as Grubb Parsons. It was based in Newcastle upon Tyne, in England. They were a noted telescope maker throughout the 19th and 20th century, making telescope th ...
. The mirror blank was produced in 1969 as one of a set of four, along with those for the AAT, CFHT and
Blanco Blanco (''white'' or ''blank'' in Spanish) or Los Blancos may refer to: People *Blanco (surname) Fictional characters *Blanco, a hobbit in J. R. R. Tolkien's Middle-earth * Blanco Webb, character in the BBC sitcom ''Porridge'' * El Blanco, albin ...
telescopes, and was purchased for the WHT in 1979, ten years after it was made. The primary is solid and un-thinned, so no
active optics Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, and mechanical stress. Without active op ...
system is required, despite its weight of . The
mirror support cell In astronomy, a mirror support cell - more commonly mirror cell - is a component of a reflecting telescope that supports the mirror in place to hold optical alignment, allow collimation adjustment, and protect it from falling out. The common usa ...
holds the main mirror on a set of 60
pneumatic cylinder Pneumatic cylinders (sometimes known as air cylinders) are mechanical devices which use the power of compressed gas to produce a force in a reciprocating linear motion. Like hydraulic cylinders, something forces a piston to move in the desire ...
s. Even under the most extreme loading (with the telescope pointing at the horizon, so the mirror is vertical) the shape of the mirror changes by only ; during normal operation the deformation is much smaller. In its most usual configuration, a
hyperbolic Hyperbolic is an adjective describing something that resembles or pertains to a hyperbola (a curve), to hyperbole (an overstatement or exaggeration), or to hyperbolic geometry. The following phenomena are described as ''hyperbolic'' because they ...
secondary mirror made of
Zerodur Zerodur (notation of the manufacturer: ZERODUR®), registered trademarkof Schott AG, is a lithium-aluminosilicate glass-ceramic produced by Schott AG since 1968. It has been used for a number of very large telescope mirrors including GTC, Keck ...
is used to form a Ritchey Chretien f/11 Cassegrain system with a 15
arcmin A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...
field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...
. An additional flat fold mirror allows the use of any one of two Nasmyth platforms or two folded Cassegrain stations, each with 5 arcmin fields of view. The telescope sometimes operates in a wide-field
prime focus A reflecting telescope (also called a reflector) 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 alternat ...
configuration, in which case the secondary is removed and a three element field-correcting lens inserted, which provides an effective f/2.8 focus with a 60 arcmin field of view (40 arcmin unvignetted). Changing between the Cassegrain and Nasmyth foci takes a matter of seconds and may be done during the night; switching to and from prime focus requires replacing the secondary mirror with a prime focus assembly during daytime (the two are mounted back-to-back) which takes around 30 minutes. A
Coudé focus A reflecting telescope (also called a reflector) 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 alternat ...
was planned as a later addition, to feed an
optical interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...
with another telescope, but this was never built. A chopping f/35 secondary mirror was planned for
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
observations, but was placed on hold by the cost-saving re-design and never implemented.


Mount

The optical system weighs and is manoeuvred on an alt-azimuth mount, with a total moving mass of (plus instruments). The
BTA-6 The BTA-6 (russian: Большой Телескоп Альт-азимутальный, translit=Bolshoi Teleskop Alt-azimutalnyi, translation=Large Altazimuth Telescope) is a aperture optical telescope at the Special Astrophysical Observatory lo ...
and Multi Mirror Telescope had demonstrated during the 1970s the significant weight (and therefore cost) savings which could be achieved by the alt-azimuth design compared to the traditional
equatorial mount An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, the polar axis, parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras. The ...
for large telescopes. However, the alt-azimuth design requires continuous computer control, compensation for field rotation at each focus, and results in a 0.2 degree radius blind spot at
zenith The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" ...
where the drive motors cannot keep up with sidereal motion (the drives have a maximum speed of one degree per second in each axis). The mount is so smooth and finely balanced that before the drive motors were installed it was possible to move the then assembly by hand. During closed loop guiding, the mount is capable of an absolute pointing accuracy of 0.03 arcseconds.


Dome

The telescope is housed in an onion-shaped steel dome with an internal diameter of , manufactured by
Brittain Steel Brittain may refer to: * Brittain (surname) * Brittain, West Virginia, United States * Brittain, Ohio, United States * Brittain Creek, a stream in North Carolina * Brittain Dining Hall * Brittain Speaker, a historical name for the Leslie speaker ...
. The telescope mount is located on a cylindrical concrete pier so that the centre of rotation is above ground level, which lifts the telescope above ground-layer air
turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
for better seeing. A conventional up-down 6m-wide shutter with wind-blind, several large vents with extractor fans for thermal control, and a capacity crane (used for moving the primary mirror e.g. for aluminising) are all incorporated. The size and shape of the shutter allow observations down to 12° above the
horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...
, which corresponds to an
airmass In astronomy, air mass or airmass is a measure of the amount of air along the line of sight when observing a star or other celestial source from below Earth's atmosphere ( Green 1992). It is formulated as the integral of air density along the lig ...
of 4.8. The total moving mass of the dome is , which is mounted on top of a three-
storey A storey (British English) or story (American English) is any level part of a building with a floor that could be used by people (for living, work, storage, recreation, etc.). Plurals for the word are ''storeys'' (UK) and ''stories'' (US). T ...
cylindrical building. The dome was designed to minimise wind stresses and can support up to its own weight again in ice during inclement weather. The dome and telescope rest on separate sets of
foundations Foundation may refer to: * Foundation (nonprofit), a type of charitable organization ** Foundation (United States law), a type of charitable organization in the U.S. ** Private foundation, a charitable organization that, while serving a good cause ...
(driven down into the volcanic basalt), to prevent vibrations caused by dome rotation or wind stresses on the building affecting the telescope pointing. Attached to the dome is a three-storey rectangular building which houses the telescope control room, computer room, kitchen etc. Almost no human presence is required inside the dome, which means the environmental conditions can be kept very stable. As a result, the WHT obtains perfect dome seeing. This building also houses a
detector A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
laboratory and a re aluminising plant. Because the WHT has the largest single mirror at the
Roque de los Muchachos Observatory Roque de los Muchachos Observatory ( es, Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated ...
, its realuminising plant has a vacuum vessel large enough to accommodate the mirrors from any other telescope on the mountain. As a result, all of the other telescopes at the observatory contract to use the WHT plant for their realuminising (with the exception of the
Gran Telescopio Canarias The Gran Telescopio Canarias (GranTeCan or GTC) is a reflecting telescope located at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain. It is the world's largest single-aperture optical telescope. Constr ...
, which has its own plant).


Operations

The WHT is operated by the
Isaac Newton Group of Telescopes The Isaac Newton Group of Telescopes or ING consists of three optical telescopes: the William Herschel Telescope, the Isaac Newton Telescope, and the Jacobus Kapteyn Telescope, operated by a collaboration between the UK Science and Technology Fac ...
(ING), together with the 2.5m
Isaac Newton Telescope The Isaac Newton Telescope or INT is a 2.54 m (100 in) optical telescope run by the Isaac Newton Group of Telescopes at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984. Originally the INT was situated at He ...
and 1.0m
Jacobus Kapteyn Telescope The Jacobus Kapteyn Telescope or JKT is a 1-metre optical telescope named for the Dutch astronomer Jacobus Kapteyn (1851-1922) of the Isaac Newton Group of Telescopes at the Roque de los Muchachos Observatory on La Palma in the Canary Islands, Sp ...
. Offices and administration are located an hour's drive away in
Santa Cruz de La Palma Santa Cruz de la Palma (Spanish for ''Holy Cross of La Palma'') is a city and a municipality on the east coast of the island of La Palma in the province of Santa Cruz de Tenerife of the Canary Islands. Santa Cruz de la Palma is the second-large ...
, the island's capital. Funding is provided by the UK's
Science and Technology Facilities Council The Science and Technology Facilities Council (STFC) is a United Kingdom government agency that carries out research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astro ...
(STFC, 65%), the Netherlands'
Nederlandse Organisatie voor Wetenschappelijk Onderzoek The Dutch Research Council (NWO, Dutch: Nederlandse Organisatie voor Wetenschappelijk Onderzoek) is the national research council of the Netherlands. NWO funds thousands of top researchers at universities and institutes and steers the course o ...
(NWO, 25%) and Spain's
Instituto de Astrofísica de Canarias The Instituto de Astrofísica de Canarias (IAC) is an astrophysical research institute located in the Canary Islands, Spain. It was founded in 1975 at the University of La Laguna. It operates two astronomical observatories in the Canary Islands: ...
(IAC, 10%) (2008 values). Telescope time is distributed in proportion to this funding, although Spain receives an additional 20% allocation in return for use of the observatory site. Five percent of observing time is further reserved for astronomers of other nationalities. As a competitive research telescope, the WHT is heavily oversubscribed, typically receiving applications for three to four times as much observing time as is actually available. The vast majority of observations are carried out in visitor mode i.e. with the investigating astronomer physically present at the telescope. A shift to service mode operations (those carried out by observatory staff on behalf of astronomers who do not travel to the telescope) has been considered and rejected on scientific and operational grounds.


Instruments

The WHT is equipped with a wide range of scientific instruments, providing a range of capabilities to astronomers. , the common-user instrumentation is: ;ACAM :Auxiliary-port CAMera – optical imager/spectrograph, with broad- and narrow-band imaging over an 8 ' field and low-
resolution Resolution(s) may refer to: Common meanings * Resolution (debate), the statement which is debated in policy debate * Resolution (law), a written motion adopted by a deliberative body * New Year's resolution, a commitment that an individual mak ...
(R < 900) spectroscopy. Permanently mounted at one of the broken-Cassegrain foci. ;ISIS :Intermediate dispersion Spectrograph and Imaging System – medium resolution (R = 1,800-20,000) long-slit dual-beam optical spectrograph. Mounted at Cassegrain focus. ISIS was one of the original first generation of WHT instruments. ;LIRIS :Long-slit Intermediate Resolution Infrared Spectrograph –
near-infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
imager/spectrograph, with imaging over a 4' field, spectral resolutions R = 700–2500,
spectropolarimetry Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or ha ...
, and long slit and multi-object slit-masks. Mounted at Cassegrain focus. ;WEAVE :WHT Enhanced Area Velocity Explorer - a multi-object optical spectrograph, which uses a robot positioner and
optical fibre An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means to ...
s to observe up to 1000 targets at a time. Beginning in 2022, 70% of the telescope's time will be dedicated to surveys with WEAVE. Prior to the installation of WEAVE (2020-22), ISIS and LIRIS were the workhorses of the WHT, with approximately two-thirds of all time awarded using those two instruments. In addition the WHT is a popular telescope for single-purpose visitor instruments, which in recent years have included PAUCam, GHαFaS, PNS, INTEGRAL,
PLANETPOL PlanetPol was a ground-based, high sensitivity polarimeter based at the William Herschel Telescope on the island of La Palma in the Canary Islands, Spain that has now been decommissioned. It was the most sensitive astronomical visual polarimeter e ...
, SAURON, FASTCAM and ULTRACAM. Visitor instruments can use either the Cassegrain focus or one of the Nasmyth foci. A common set of calibration lamps (Helium and Neon
arc lamp An arc lamp or arc light is a lamp that produces light by an electric arc (also called a voltaic arc). The carbon arc light, which consists of an arc between carbon electrodes in air, invented by Humphry Davy in the first decade of the 1800s, ...
s, and a Tungsten flat-field lamp) are permanently mounted at one of the broken-Cassegrain foci, and can be used for any of the other instruments.


Scientific research

Astronomers use the WHT to conduct scientific research across most branches of
observational astronomy Observational astronomy is a division of astronomy that is concerned with recording data about the observable universe, in contrast with theoretical astronomy, which is mainly concerned with calculating the measurable implications of physical m ...
, including
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
science,
galactic astronomy Galactic astronomy is the study of the Milky Way galaxy and all its contents. This is in contrast to extragalactic astronomy, which is the study of everything outside our galaxy, including all other galaxies. Galactic astronomy should not be co ...
, extragalactic astronomy and
cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...
. Most of the instruments are designed to be useful for a range of different research. The WHT has been used to make many significant new discoveries. Some of the more notable include the first evidence of a
supermassive black hole A supermassive black hole (SMBH or sometimes SBH) is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions of times the mass of the Sun (). Black holes are a class of astronomical obj ...
(
Sgr A* Sagittarius A* ( ), abbreviated Sgr A* ( ), is the supermassive black hole at the Galactic Center of the Milky Way. It is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic, vi ...
) at the
centre Center or centre may refer to: Mathematics * Center (geometry), the middle of an object * Center (algebra), used in various contexts ** Center (group theory) ** Center (ring theory) * Graph center, the set of all vertices of minimum eccentri ...
of the
Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...
(in 1995) and the first
optical Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
observation of a
gamma-ray burst In gamma-ray astronomy, gamma-ray bursts (GRBs) are immensely energetic explosions that have been observed in distant galaxies. They are the most energetic and luminous electromagnetic events since the Big Bang. Bursts can last from ten milli ...
(
GRB 970228 GRB 970228"GRB" indicates that the event was a gamma-ray burst, and the numbers follow a YYMMDD format corresponding to the date on which the burst occurred: 28 February 1997. was the first gamma-ray burst (GRB) for which an afterglow was observe ...
) (in 1997). Since the mid-1990s the WHT has faced increasing competition from newer telescopes. Nevertheless, a wide range of research continues to be done with the telescope. In recent years () this has included: * The SAURON project, an
integral field spectrograph Integral Field Spectrographs (IFS) combine spectrographic and imaging capabilities in the optical or infrared wavelength domains -from 0.32 μm to 24 μm- to get from a single exposure spatially resolved spectra in a bi-dimensional region. Develop ...
survey of nearby
elliptical Elliptical may mean: * having the shape of an ellipse, or more broadly, any oval shape ** in botany, having an elliptic leaf shape ** of aircraft wings, having an elliptical planform * characterised by ellipsis (the omission of words), or by conc ...
and
lenticular galaxies A lenticular galaxy (denoted S0) is a type of galaxy intermediate between an elliptical (denoted E) and a spiral galaxy in galaxy morphological classification schemes. It contains a large-scale disc but does not have large-scale spiral arms. ...
(2001–2010) * The first spectrum of an asteroid which subsequently hit Earth, (2009) * The first
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
of
Hanny's Voorwerp , (Dutch for ''Hanny's object'') is a rare type of astronomical object called a quasar ionization echo. It was discovered in 2007 by Dutch schoolteacher Hanny van Arkel while she was participating as a volunteer in the Galaxy Zoo project, part ...
(2009) * The discovery that
diffuse interstellar bands Diffuse interstellar bands (DIBs) are absorption features seen in the spectra of astronomical objects in the Milky Way and other galaxies. They are caused by the absorption of light by the interstellar medium. Circa 500 bands have now been se ...
do not originate in
circumstellar envelope A circumstellar envelope (CSE) is a part of a star that has a roughly spherical shape and is not gravitationally bound to the star core. Usually circumstellar envelopes are formed from the dense stellar wind, or they are present before the formatio ...
s (2008) * Confirmation that
WASP-3b WASP-3b is an extrasolar planet orbiting the star WASP-3 located approximately 800 light-years away in the constellation Lyra. It was discovered via the transit method by SuperWASP, and follow up radial velocity observations confirmed that WASP-3 ...
is an
extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
(2008) * High-resolution spectra of the first known double
supernova A supernova is a powerful and luminous explosion of a star. It has the plural form supernovae or supernovas, and is abbreviated SN or SNe. This transient astronomical event occurs during the last evolutionary stages of a massive star or when ...
,
SN 2006jc SN 2006jc was a supernova that was detected on October 9, 2006 in the galaxy UGC 4904, which is about 77 million light-years away in the constellation Lynx. It was first seen by Japanese amateur astronomer Koichi Itagaki, American amateur Tim Pu ...
(2007)


Future developments

The upcoming generation of
extremely large telescope The Extremely Large Telescope (ELT) is an astronomical observatory currently under construction. When completed, it is planned to be the world's largest optical/near-infrared extremely large telescope. Part of the European Southern Observator ...
s (ELTs) will require sophisticated
adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...
in order to be used to their full capability. Because the WHT had an advanced adaptive optics system operating, it has received attention from the various ELT programs. , the
European Southern Observatory The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental organization, intergovernmental research organisation made up of 16 mem ...
's European-ELT (E-ELT) project had a programme to utilise the WHT as a test-bed for its adaptive optics system, and received several nights per year for on-sky testing. The project involves construction of new optical experiments at one of the Nasmyth foci, and is called CANARY. CANARY will demonstrate the multi-object adaptive optics (MOAO) required for the EAGLE instrument on the E-ELT. The UK's STFC (originally the major financial contributor) has gradually reduced its funding for the ING telescopes over a number of years. Some of this funding shortfall has been made up by other partners increasing their contributions, and some by efficiency savings and cutbacks. As a result, the shares of observing time will become UK 33%, Netherlands 28%, Spain 34% and 5% for any nationality. A new development, started in 2010, is the development of a new wide-field multi-object spectroscopy facility (WEAVE), being developed by a UK-led consortium involving major contributions from the Netherlands, Spain, France, and Italy, the final installation of which was confirmed in August 2022. WEAVE will provide medium-high resolution spectroscopy in the visible (360–950 nm) range for up to 1000 simultaneous targets over a 2 degree field of view, and is currently expected to operate for several years.


See also

*
List of largest optical reflecting telescopes A ''list'' is any set of items in a row. List or lists may also refer to: People * List (surname) Organizations * List College, an undergraduate division of the Jewish Theological Seminary of America * SC Germania List, German rugby union ...


Notes


References


External links

*
WHT Homepage

Images of the WHT
* {{good article Astronomical observatories in La Palma Science and Technology Facilities Council Optical telescopes