William Herschel Telescope
Encyclopedia
The William Herschel Telescope (WHT) is a 4.2 m (165.4 in) optical/near-infrared
reflecting telescope
located at the Observatorio del Roque de los Muchachos on the island of La Palma
in the Canary Islands
, Spain. The telescope, which is named after William Herschel
, is part of the Isaac Newton Group of Telescopes
. 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
(6.0m) and Hale telescope
(5.1m) were both larger; the Multiple Mirror Telescope also had a larger collecting area but did not have a single primary mirror It is currently the second largest in Europe,The GTC
(10.4m) overtook the WHT in 2009 to become the largest in Europe and was the final telescope constructed by Grubb Parsons in their 150 year history.
The WHT is equipped with a wide range of instruments operating over the optical and near-infrared
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
(Sgr A*) at the centre of the Milky Way
, and made the first optical observation of a gamma-ray burst.
(AAT) was being designed. The British astronomical community saw the need for telescopes of comparable power in the northern hemisphere
. In particular, there was a need for optical follow-up of interesting sources in the radio surveys
being conducted at the Jodrell Bank and Mullard
observatories, both located in the UK.
The AAT was completed in 1974, at which point the British Science and Engineering Research Council
began planning for a group of three telescopes located in the northern hemisphere (now known as the Isaac Newton Group of Telescopes
, ING). The telescopes were to be a 1 m (39.4 in) (which became the Jacobus Kapteyn Telescope
), the 2.5 m (98.4 in) Isaac Newton Telescope
which was to be moved from its existing site at Herstmonceux Castle
, and a 4m class telescope, initially planned as a 4.5 m (177.2 in). A new site was chosen at an altitude of 2344 m (7,690.3 ft) on the island of La Palma
in the Canary Islands
, that is now the Observatorio del Roque de los Muchachos. 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 4.2 m (165.4 in). 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
of the telescope – which allowed the use of a smaller dome – and relocating non-essential functions outside the dome to a simpler (and thus cheaper) rectangular annexe. In the same year, the Isaac Newton Telescope
was moved to Roque de los Muchachos Observatory
, becoming the first of the Isaac Newton Group of Telescopes
. In 1981 the Nederlandse Organisatie voor Wetenschappelijk Onderzoek
(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
, and it was decided to name the telescope in his honour.
Construction of the telescope was by Grubb Parsons, the last telescope that company produced in its 150 year history. Work began at their workshop in Newcastle-upon-Tyne in 1983, and the telescope was shipped to La Palma
in 1985 (the two other telescopes of the Isaac Newton Group began operating in 1984). The WHT saw first light on 1st 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.
from Cervit, a zero-expansion glass-ceramic
material, and ground by Grubb Parsons. The mirror blank was produced in 1969 as one of a set of four, along with those for the AAT
, CFHT and Blanco 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
system is required, despite its weight of 16.5 tonne. Support for the main mirror is provided by a set of 60 pneumatic cylinder
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 50 nanometre (5E-08 m); during normal operation the deformation is much smaller.
In its most usual configuration, a 1 m (39.4 in) hyperbolic
secondary mirror made of Zerodur
is used to form a Ritchey Chretien f/11 Cassegrain
system with a 15 arcmin field of view
. 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 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 was planned as a later addition, to feed an optical interferometer with another telescope, but this was never built. A chopping f/35 secondary mirror was planned for infrared
observations, but was placed on hold by the cost-saving re-design and never implemented.
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
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
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 160 long ton assembly by hand. During closed loop guiding
, the mount is capable of an absolute pointing accuracy of 0.03 arcseconds.
The telescope is housed in an onion-shaped
steel dome with an internal diameter of 21 m (68.9 ft), manufactured by Brittain Steel. The telescope mount is located on a cylindrical concrete pier so that the centre of rotation is 13.4 m (44 ft) above ground level, which lifts the telescope above ground-layer
air turbulence
for better seeing. A conventional up-down 6m-wide shutter with wind-blind, several large vents with extractor fans for thermal control, and a 35 tonne 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
, which corresponds to an airmass
of 4.8. The total moving mass of the dome is 320 tonne, which is mounted on top of a three-storey
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 (driven 20 metres (65.6 ft) 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
laboratory and a realuminising plant. Because the WHT has the largest single mirror at the Observatorio del Roque de los Muchachos, 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
, which has its own plant).
The WHT is operated by the Isaac Newton Group of Telescopes
(ING), together with the 2.5m Isaac Newton Telescope
and 1.0m Jacobus Kapteyn Telescope
. Offices and administration are located an hour's drive away in Santa Cruz de La Palma
, the island's capital. Funding is provided by the UK's Science and Technology Facilities Council
(STFC, 65%), the Netherland's Nederlandse Organisatie voor Wetenschappelijk Onderzoek
(NWO, 25%) and Spain's Instituto de Astrofísica de Canarias
(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.
ACAM
AF2
ISIS
LIRIS
NAOMI
PFIP
In addition the WHT is a popular telescope for single-purpose visitor instruments, which in recent years have included GHαFaS, INTEGRAL, PLANETPOL
, PNS, 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
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.
The ISIS and LIRIS are the workhorses of the WHT, and approximately two-thirds of all time awarded is for these two instruments.
Astronomers use the WHT to conduct scientific research across most branches of observational astronomy
, including solar system
science, galactic astronomy
, extragalactic astronomy
and cosmology
. 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
(Sgr A*) at the centre of the Milky Way
(in 1995) and the first optical observation of a gamma-ray burst (GRB 970228
) (in 1997).
Since the mid-1990s the WHT has faced increasing competition from newer 8 to 10 m (315 to 393.7 in) telescopes. Nevertheless, a wide range of research continues to be done with the telescope. In recent years this has included:
s (ELTs) will require sophisticated adaptive optics
in order to be used to their full capability. Because the WHT has an advanced adaptive optics system already operating, it is receiving attention from the various ELT programs. The European Southern Observatory
's European-ELT (E-ELT) project has begun a programme to utilise the WHT as a test-bed for its adaptive optics system, and will receive 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. UK funding will continue until at least May 2012, but at a reduced level. As a result, the shares of observing time will become UK 33%, Netherlands 28%, Spain 34% and 5% for any nationality.
Infrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
located at the Observatorio del Roque de los Muchachos on the island of La Palma
La Palma
La Palma is the most north-westerly of the Canary Islands. La Palma has an area of 706 km2 making it the fifth largest of the seven main Canary Islands...
in the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
, Spain. The telescope, which is named after William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel 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...
, is part of the Isaac Newton Group of Telescopes
Isaac Newton Group of Telescopes
The Isaac Newton Group of Telescopes or ING operates the William Herschel Telescope, Isaac Newton Telescope and Jacobus Kapteyn Telescope optical telescopes for the Science and Technology Facilities Council , the NWO and the IAC...
. 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
BTA-6
The BTA-6 is a 6 m aperture optical telescope at the Special Astrophysical Observatory located in the Zelenchuksky District on the north side of the Caucasus Mountains in southern Russia...
(6.0m) and Hale telescope
Hale telescope
The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...
(5.1m) were both larger; the Multiple Mirror Telescope also had a larger collecting area but did not have a single primary mirror It is currently the second largest in Europe,The GTC
Gran Telescopio Canarias
The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
(10.4m) overtook the WHT in 2009 to become the largest in Europe and was the final telescope constructed by Grubb Parsons in their 150 year history.
The WHT is equipped with a wide range of instruments operating over the optical and near-infrared
Infrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
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
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
(Sgr A*) at the centre of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
, and made the first optical observation of a gamma-ray burst.
History
The WHT was first conceived in the late 1960s, when the 3.9 m (153.5 in) Anglo-Australian TelescopeAnglo-Australian Telescope
The Anglo-Australian Telescope is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m...
(AAT) was being designed. The British astronomical community saw the need for telescopes of comparable power in the northern hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
. In particular, there was a need for optical follow-up of interesting sources in the radio surveys
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
being conducted at the Jodrell Bank and Mullard
Mullard Radio Astronomy Observatory
Mullard Radio Astronomy Observatory is home to a number of large aperture synthesis radio telescopes, including the One-Mile Telescope, 5-km Ryle Telescope, and the Arcminute Microkelvin Imager...
observatories, both located in the UK.
The AAT was completed in 1974, at which point the British Science and Engineering Research Council
Science and Engineering Research Council
The Science and Engineering Research Council used to be the UK agency in charge of publicly funded scientific and engineering research activities including astronomy, biotechnology and biological sciences, space research and particle physics...
began planning for a group of three telescopes located in the northern hemisphere (now known as the Isaac Newton Group of Telescopes
Isaac Newton Group of Telescopes
The Isaac Newton Group of Telescopes or ING operates the William Herschel Telescope, Isaac Newton Telescope and Jacobus Kapteyn Telescope optical telescopes for the Science and Technology Facilities Council , the NWO and the IAC...
, ING). The telescopes were to be a 1 m (39.4 in) (which became the Jacobus Kapteyn Telescope
Jacobus Kapteyn Telescope
The Jacobus Kapteyn Telescope or JKT is a 1m optical telescope of the Isaac Newton Group of Telescopes on La Palma in the Canary Islands. It was funded by Netherlands and the United Kingdom and completed in the early 1980s. Planning procceded throughout the 1970s and it came online in 1983-1984...
), the 2.5 m (98.4 in) Isaac Newton Telescope
Isaac Newton Telescope
The Isaac Newton Telescope or INT is a 2.54 m optical telescope run by the ING at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984....
which was to be moved from its existing site at Herstmonceux Castle
Herstmonceux Castle
Herstmonceux Castle is a brick-built Tudor castle near Herstmonceux, East Sussex, United Kingdom. From 1957 to 1988 its grounds were the home of the Royal Greenwich Observatory...
, and a 4m class telescope, initially planned as a 4.5 m (177.2 in). A new site was chosen at an altitude of 2344 m (7,690.3 ft) on the island of La Palma
La Palma
La Palma is the most north-westerly of the Canary Islands. La Palma has an area of 706 km2 making it the fifth largest of the seven main Canary Islands...
in the Canary Islands
Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
, that is now the Observatorio del Roque de los Muchachos. 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 4.2 m (165.4 in). 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
Focal length
The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...
of the telescope – which allowed the use of a smaller dome – and relocating non-essential functions outside the dome to a simpler (and thus cheaper) rectangular annexe. In the same year, the Isaac Newton Telescope
Isaac Newton Telescope
The Isaac Newton Telescope or INT is a 2.54 m optical telescope run by the ING at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984....
was moved to Roque de los Muchachos Observatory
Roque de los Muchachos Observatory
Roque de los Muchachos Observatory is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands...
, becoming the first of the Isaac Newton Group of Telescopes
Isaac Newton Group of Telescopes
The Isaac Newton Group of Telescopes or ING operates the William Herschel Telescope, Isaac Newton Telescope and Jacobus Kapteyn Telescope optical telescopes for the Science and Technology Facilities Council , the NWO and the IAC...
. In 1981 the Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
The Nederlandse Organisatie voor Wetenschappelijk Onderzoek is a scientific research organization in the Netherlands....
(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
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel 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...
, and it was decided to name the telescope in his honour.
Construction of the telescope was by Grubb Parsons, the last telescope that company produced in its 150 year history. Work began at their workshop in Newcastle-upon-Tyne in 1983, and the telescope was shipped to La Palma
La Palma
La Palma is the most north-westerly of the Canary Islands. La Palma has an area of 706 km2 making it the fifth largest of the seven main Canary Islands...
in 1985 (the two other telescopes of the Isaac Newton Group began operating in 1984). The WHT saw first light on 1st 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 4.2 m (165.4 in) f/2.5 primary mirror made by Owens-IllinoisOwens-Illinois
Owens-Illinois Inc. is a Fortune 500 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 America, Asia-Pacific and Europe...
from Cervit, a zero-expansion glass-ceramic
Glass-ceramic
Glass-ceramics are polycrystalline material produced through controlled crystallization of base glass. Glass-ceramic materials share many properties with both glasses and ceramics...
material, and ground by Grubb Parsons. The mirror blank was produced in 1969 as one of a set of four, along with those for the AAT
Anglo-Australian Telescope
The Anglo-Australian Telescope is a 3.9 m equatorially mounted telescope operated by the Australian Astronomical Observatory and situated at the Siding Spring Observatory, Australia at an altitude of a little over 1100 m...
, CFHT and Blanco 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
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, mechanical stress...
system is required, despite its weight of 16.5 tonne. Support for the main mirror is provided by a set of 60 pneumatic cylinder
Pneumatic cylinder
Pneumatic cylinders are mechanical devices which utilize the power of compressed gas to produce a force in a reciprocating linear motion....
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 50 nanometre (5E-08 m); during normal operation the deformation is much smaller.
In its most usual configuration, a 1 m (39.4 in) hyperbolic
Hyperbola
In mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...
secondary mirror made of Zerodur
Zerodur
Zerodur®, a registered trademark of Schott Glass Technologies, 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 Keck I and Keck II. With its very low coefficient of expansion it can be used to...
is used to form a Ritchey Chretien f/11 Cassegrain
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....
system with a 15 arcmin field of view
Field of view
The field of view is the extent of the observable world that is seen at any given moment....
. An additional flat fold mirror allows the use of any one of two Nasmyth
Nasmyth telescope
The Nasmyth telescope, also called Nasmyth-Cassegrain, is a reflecting telescope developed by James Nasmyth. It is a modified form of a Cassegrain telescope, mounted on an alt-azimuth mount.-Scheme:...
platforms or two folded Cassegrain stations, each with 5 arcmin fields of view. The telescope sometimes operates in a wide-field prime focus configuration, in which case the secondary is removed and a three element field-correcting lens
Field Flattener Lens
Field flattener lens is a type of lens used in modern binocular designs and in astronomic telescopes....
inserted, which provides an effective f/2.8 focus with a 60 arcmin field of view (40 arcmin unvignetted
Vignetting
In photography and optics, vignetting is a reduction of an image's brightness or saturation at the periphery compared to the image center. The word vignette, from the same root as vine, originally referred to a decorative border in a book. Later, the word came to be used for a photographic...
). 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 was planned as a later addition, to feed an optical interferometer with another telescope, but this was never built. A chopping f/35 secondary mirror was planned for infrared
Infrared astronomy
Infrared astronomy is the branch of astronomy and astrophysics that studies astronomical objects visible in infrared radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers...
observations, but was placed on hold by the cost-saving re-design and never implemented.
Mount
The optical system weighs 79513 kg (78.3 LT) and is manoeuvred on an alt-azimuth mount, with a total moving mass of 186250 kg (183.3 LT) (plus instruments). The BTA-6BTA-6
The BTA-6 is a 6 m aperture optical telescope at the Special Astrophysical Observatory located in the Zelenchuksky District on the north side of the Caucasus Mountains in southern Russia...
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
Equatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
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
Blind spot
Blind spot may refer to:In ophthalmology:*Scotoma, an obscuration of the visual field*Optic disc, also known as the anatomical blind spot, the specific region of the retina where the optic nerve and blood vessels pass through to connect to the back of the eye*Blind spot , also known as the...
at zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
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 160 long ton assembly by hand. During closed loop guiding
Guide star
In astronomy, a guide star is a reference star used to accurately maintain the tracking by a telescope of a heavenly body, whose motion across the sky is primarily due to the rotation of the Earth....
, the mount is capable of an absolute pointing accuracy of 0.03 arcseconds.
Dome
Onion dome
An onion dome is a dome whose shape resembles the onion, after which they are named. Such domes are often larger in diameter than the drum upon which they are set, and their height usually exceeds their width...
steel dome with an internal diameter of 21 m (68.9 ft), manufactured by Brittain Steel. The telescope mount is located on a cylindrical concrete pier so that the centre of rotation is 13.4 m (44 ft) above ground level, which lifts the telescope above ground-layer
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
air turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
for better seeing. A conventional up-down 6m-wide shutter with wind-blind, several large vents with extractor fans for thermal control, and a 35 tonne 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
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
, which corresponds to an airmass
Airmass
In astronomy, air mass is the optical path length through Earth’s atmosphere for light from a celestial source. As it passes through the atmosphere, light is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Consequently, celestial...
of 4.8. The total moving mass of the dome is 320 tonne, which is mounted on top of a three-storey
Storey
A storey or story is any level part of a building that could be used by people...
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 (driven 20 metres (65.6 ft) 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
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
laboratory and a realuminising plant. Because the WHT has the largest single mirror at the Observatorio del Roque de los Muchachos, 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
Gran Telescopio Canarias
The Gran Telescopio Canarias , also known as GranTeCan or GTC, is a reflecting telescope undertaking commissioning observations at the Roque de los Muchachos Observatory on the island of La Palma, in the Canary Islands of Spain, as of July 2009.Construction of the telescope, sited on a volcanic...
, which has its own plant).
Operations
Isaac Newton Group of Telescopes
The Isaac Newton Group of Telescopes or ING operates the William Herschel Telescope, Isaac Newton Telescope and Jacobus Kapteyn Telescope optical telescopes for the Science and Technology Facilities Council , the NWO and the IAC...
(ING), together with the 2.5m Isaac Newton Telescope
Isaac Newton Telescope
The Isaac Newton Telescope or INT is a 2.54 m optical telescope run by the ING at Roque de los Muchachos Observatory on La Palma in the Canary Islands since 1984....
and 1.0m Jacobus Kapteyn Telescope
Jacobus Kapteyn Telescope
The Jacobus Kapteyn Telescope or JKT is a 1m optical telescope of the Isaac Newton Group of Telescopes on La Palma in the Canary Islands. It was funded by Netherlands and the United Kingdom and completed in the early 1980s. Planning procceded throughout the 1970s and it came online in 1983-1984...
. Offices and administration are located an hour's drive away in Santa Cruz de La Palma
Santa Cruz de La Palma
Santa Cruz de la Palma is located on the eastern part 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 largest city and is the capital of the island...
, the island's capital. Funding is provided by the UK's Science and Technology Facilities Council
Science and Technology Facilities Council
The Science and Technology Facilities Council is a UK government body that carries out civil research in science and engineering, and funds UK research in areas including particle physics, nuclear physics, space science and astronomy .-History:It was formed in April 2007 as a merger of the Particle...
(STFC, 65%), the Netherland's Nederlandse Organisatie voor Wetenschappelijk Onderzoek
Nederlandse Organisatie voor Wetenschappelijk Onderzoek
The Nederlandse Organisatie voor Wetenschappelijk Onderzoek is a scientific research organization in the Netherlands....
(NWO, 25%) and Spain's Instituto de Astrofísica de Canarias
Instituto de Astrofísica de Canarias
The Instituto de Astrofísica de Canarias is an astrophysical research institute located in Tenerife 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 astronomers with the capabilities to conduct a large variety of scientific investigations. The current common-user instrumentation is:ACAM
- Auxiliary-port CAMera - optical imager/spectrograph, with broad- and narrow-band imaging over a 8' field and low-resolutionSpectral resolutionThe spectral resolution of a spectrograph, or, more generally, of a frequency spectrum, is a measure of its ability to resolve features in the electromagnetic spectrum...
(R < 900) spectroscopy. Permanently mounted at one of the broken-Cassegrain foci.
AF2
- Autofib2 - robot fibre positioner, 150 science fibres and 10 fiducial bundles over a 1°Degree (angle)A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians...
field. Mounted at prime focus.- WYFFOS
- :Wide field Fibre Fed Optical Spectrograph - bench-mounted optical spectrograph fed from AF2, R = 200-11,000. Located in one of the Nasmyth enclosures, though it does not use the Nasmyth focus
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 imager/spectrograph, with imaging over a 4' field, spectral resolutions R = 700-2500, spectropolarimetry, and long slit and multi-object slit-masks. Mounted at Cassegrain focus.
NAOMI
- Natural-guide-star Adaptive Optics for Multi-purpose Instrumentation - an adaptive opticsAdaptive opticsAdaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
feed, operating over the entire optical and near-infrared wavelength regions. Permanently mounted at one of the Nasmyth foci.- GLAS
- :Ground-layer Laser Adaptive optics System - laser guide starLaser guide starLaser guide stars are a form of artificial star created for use in astronomical adaptive optics imaging.Adaptive optics systems require a wavefront reference source in order to correct atmospheric distortion of light...
for optional use with NAOM - INGRID
- :Isaac Newton Group Red Imaging Device - high spatial resolution near-infrared camera for use with NAOM
- ;OSCA
- ::Optimised Stellar Coronograph for Adaptive Optics - high-contrast coronograph for optional use with INGRI
- OASIS
- :Optically Adaptive System for Imaging Spectroscopy - optical integral field unit for use with NAOM
PFIP
- Prime Focus Imaging Platform - wide field optical camera, with broad- and narrow-band imaging over a 16' field. Mounted at prime focus.
In addition the WHT is a popular telescope for single-purpose visitor instruments, which in recent years have included GHαFaS, INTEGRAL, PLANETPOL
PlanetPol
PlanetPol is a ground based extrasolar planet search device. Based at William Herschel Telescope....
, PNS, 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
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...
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.
The ISIS and LIRIS are the workhorses of the WHT, and approximately two-thirds of all time awarded is for these two instruments.
Scientific research
Observational astronomy
Observational astronomy is a division of the astronomical science that is concerned with getting data, in contrast with theoretical astrophysics which is mainly concerned with finding out the measurable implications of physical models...
, including solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
science, galactic astronomy
Galactic astronomy
Galactic astronomy is the study of our own 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....
, extragalactic astronomy
Extragalactic astronomy
Extragalactic astronomy is the branch of astronomy concerned with objects outside our own Milky Way Galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy, the next level of galactic astronomy....
and cosmology
Cosmology
Cosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
. 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
Supermassive black hole
A supermassive black hole is the largest type of black hole in a galaxy, in the order of hundreds of thousands to billions of solar masses. Most, and possibly all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.Supermassive black holes have...
(Sgr A*) at the centre of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...
(in 1995) and the first optical observation of a gamma-ray burst (GRB 970228
GRB 970228
GRB 970228 was the first gamma-ray burst for which an afterglow was observed. It was detected on 28 February 1997 at 02:58 UTC. Since 1993, physicists had predicted GRBs to be followed by a lower-energy afterglow , but until this event, GRBs had only been observed in highly luminous bursts of...
) (in 1997).
Since the mid-1990s the WHT has faced increasing competition from newer 8 to 10 m (315 to 393.7 in) 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 spectrographIntegral field spectrographAn integral field spectrograph or a spectrograph equipped with an integral field unit is an optical instrument combining spectrographic and imaging capabilities, used to obtain spatially resolved spectra in astronomy and other fields of research such as bio-medical science and earth observation...
survey of nearby ellipticalElliptical galaxyAn elliptical galaxy is a galaxy having an approximately ellipsoidal shape and a smooth, nearly featureless brightness profile. They range in shape from nearly spherical to highly flat and in size from hundreds of millions to over one trillion stars...
and lenticular galaxiesLenticular galaxyA lenticular galaxy is a type of galaxy which is intermediate between an elliptical galaxy and a spiral galaxy in galaxy morphological classification schemes. Lenticular galaxies are disk galaxies which have used up or lost most of their interstellar matter and therefore have very little ongoing...
(2001–2010) - The first spectrum of an asteroid which subsequently hit the Earth, (2009)
- The first spectrumSpectrumA spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
of Hanny's VoorwerpHanny's Voorwerp' , Dutch for Hanny's object, is an astronomical object of unknown nature. It was discovered in 2007 by Dutch school teacher Hanny van Arkel, while she was participating as an amateur volunteer in the Galaxy Zoo project...
(2009) - The discovery that diffuse interstellar bands do not originate in circumstellar envelopeCircumstellar envelopeCircumstellar envelope is the part of the star,having roughly spherical shape and not gravitationally bound to the star core.Usually circumstellar envelopes are formed from the dense stellar wind or presentbefore formation of the star...
s (2008) - Confirmation that WASP-3bWASP-3bWASP-3b is an extrasolar planet orbiting the star WASP-3 located over 727 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-3b is a planet. The planet's mass and radius indicate that it...
is an extrasolar planetExtrasolar planetAn extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
(2008) - High-resolution spectraSpectrumA spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
of the first known double supernovaSupernovaA supernova is a stellar explosion that is more energetic than a nova. It is pronounced with the plural supernovae or supernovas. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months...
, SN 2006jc (2007)
Future developments
The upcoming generation of extremely large telescopeExtremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
s (ELTs) will require sophisticated adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
in order to be used to their full capability. Because the WHT has an advanced adaptive optics system already operating, it is receiving attention from the various ELT programs. The European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...
's European-ELT (E-ELT) project has begun a programme to utilise the WHT as a test-bed for its adaptive optics system, and will receive 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. UK funding will continue until at least May 2012, but at a reduced level. As a result, the shares of observing time will become UK 33%, Netherlands 28%, Spain 34% and 5% for any nationality.