South Pole Telescope
Encyclopedia
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Metre
The metre , symbol m, is the base unit of length in the International System of Units . Originally intended to be one ten-millionth of the distance from the Earth's equator to the North Pole , its definition has been periodically refined to reflect growing knowledge of metrology...
(394 in
Inch
An inch is the name of a unit of length in a number of different systems, including Imperial units, and United States customary units. There are 36 inches in a yard and 12 inches in a foot...
) diameter telescope located at the Amundsen-Scott South Pole Station
Amundsen-Scott South Pole Station
The Amundsen–Scott South Pole Station is the American scientific research station on the high plateau of Antarctica. This station is located at the southernmost place on the Earth, the Geographic South Pole, at an elevation of 2,835 meters above sea level.The original Amundsen-Scott Station was...
, Antarctica. It is a microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
/millimetre-wave
Extremely high frequency
Extremely high frequency is the highest radio frequency band. EHF runs the range of frequencies from 30 to 300 gigahertz, above which electromagnetic radiation is considered to be low infrared light, also referred to as terahertz radiation...
telescope that observes in a frequency range between 70 and 300 GHz. The primary science goal for SPT is to conduct a survey to find several thousand clusters of galaxies, which should allow interesting constraints on the Dark Energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
equation of state.
The project is a collaboration between the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
, the University of California-Berkeley, Case Western Reserve University
Case Western Reserve University
Case Western Reserve University is a private research university located in Cleveland, Ohio, USA...
, the University of Illinois at Urbana-Champaign
University of Illinois at Urbana-Champaign
The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...
, the Smithsonian Astrophysical Observatory
Smithsonian Astrophysical Observatory
The Smithsonian Astrophysical Observatory is a research institute of the Smithsonian Institution headquartered in Cambridge, Massachusetts, where it is joined with the Harvard College Observatory to form the Harvard-Smithsonian Center for Astrophysics .-History:The SAO was founded in 1890 by...
, the University of Colorado-Boulder, McGill University
McGill University
Mohammed Fathy is a public research university located in Montreal, Quebec, Canada. The university bears the name of James McGill, a prominent Montreal merchant from Glasgow, Scotland, whose bequest formed the beginning of the university...
, and University of California at Davis. It is funded by the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
.
Microwave/millimeter-wave observations at the South Pole
The South Pole is the premier observing site in the world for millimeter-wavelength observations. The Pole's high altitude (2.8 kmKM
KM, Km, or km may stand for:*Kilometre *Kernel methods*Kettle Moraine High School*Khmer language *Kuomintang , a centre-right political party in the Republic of China on Taiwan...
/1.7 mi
Mile
A mile is a unit of length, most commonly 5,280 feet . The mile of 5,280 feet is sometimes called the statute mile or land mile to distinguish it from the nautical mile...
above sea level) means the atmosphere is thin, and the extreme cold keeps the amount of water vapor in the air low. This is particularly important for observing at millimeter wavelengths, where incoming signals can be absorbed by water vapor
Water absorption
During the transmission of electromagnetic radiation through a medium containing water molecules, portions of the electromagnetic spectrum are absorbed by water molecules...
, and where water vapor emits radiation that can be confused with astronomical signals. Because the sun does not rise and set daily, the atmosphere at the pole is particularly stable. Further, there is no interference from the sun in the millimeter range during the months of polar night.
The telescope
The telescope is a 10 meter (394 in) off-axis Gregorian telescopeGregorian telescope
The Gregorian telescope is a type of reflecting telescope designed by Scottish mathematician and astronomer James Gregory in the 17th century, and first built in 1673 by Robert Hooke...
in an altazimuth mount
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
(at the poles, an altazimuth mount is effectively identical to an 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...
). It was designed to allow a large field of view (about 1 square degree) while minimizing systematic uncertainties from ground spill-over and scattering off the telescope optics. The surface of the telescope mirror is smooth down to roughly 25 micrometers (one one-thousandth of an inch), which allows sub-millimeter wavelength observations. The secondary mirror is cooled to 10°K, and metal mesh filters
Metal mesh optical filters
Metal-mesh optical filters are optical filters made from stacks of metal meshes and dielectric. They are used as part of an optical path to filter the incoming light to allow frequencies of interest to pass while reflecting other frequencies of light....
block excess high frequency radiation to keep the thermal loading on the camera down. A key advantage of the SPT observing strategy is that the entire telescope is scanned, so the beam does not move relative to the telescope mirrors. The fast scanning of the telescope and its large field of view makes SPT efficient at surveying large areas of sky, which is required to achieve the science goals of the SPT cluster survey.
Due to its location, only the southern celestial sky can be observed. The northern sky is permanently inaccessible.
The camera
The focal plane for SPT is a 960 element bolometerBolometer
A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance. It was invented in 1878 by the American astronomer Samuel Pierpont Langley...
array of superconducting transition edge sensors (TES), which makes it one of the largest TES bolometer arrays ever built. The focal plane for SPT is split up into six pie-shaped wedges, each with 160 detectors. These wedges observe at three different frequencies: 95 GHz, 150 GHz, and 220 GHz. The modularity of the focal plane allows it to be broken into many different frequency configurations. Currently (2009 season), the SPT focal plane has one wedge at 95 GHz, four at 150 GHz, and one at 220 GHz.
Science goals
The first key project for the SPT will be a >1000 square degreeSquare degree
A square degree is a non-SI unit measure of solid angle. It is denoted in various ways, including deg2, sq.deg. and ². Just as degrees are used to measure parts of a circle, square degrees are used to measure parts of a sphere. Analogous to one degree being equal to π /180 radians, a...
survey to search for clusters of galaxies using the Sunyaev-Zel'dovich effect
Sunyaev-Zel'dovich effect
The Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...
, a distortion of the cosmic microwave background radiation
Cosmic microwave background radiation
In cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
(CMB) due to interactions between CMB photons and the hot, ionized gas in clusters. Given three years of observing the South Pole Telescope should find several thousand clusters of galaxies over an extremely wide redshift range, which should allow interesting constraints on the Dark Energy
Dark energy
In physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
equation of state.
The Atacama Cosmology Telescope
Atacama Cosmology Telescope
The Atacama Cosmology Telescope is a six-metre telescope on Cerro Toco in the Atacama Desert in the north of Chile, near the Llano de Chajnantor Observatory. It is designed to make high-resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation...
has similar, but complementary, science objectives.
Current status
The South Pole Telescope achieved first light on February 16, 2007, and began science observations in March 2007. Commissioning observations and an initial small survey were completed in austral winter 2007 with winter-overs Stephen Padin and Zak Staniszewski at its helm. Larger survey fields were completed in 2008 with winter-overs Keith Vanderlinde and Dana Hrubes, and in 2009 with winter-overs Erik Shirokoff and Ross Williamson. The camera was upgraded again in December 2009 for the 2010 observing season, and survey fields are currently being observed with 2010 and 2011 winter-overs Dana Hrubes and Daniel Luong-Van.See also
- Cosmic microwave background radiationCosmic microwave background radiationIn cosmology, cosmic microwave background radiation is thermal radiation filling the observable universe almost uniformly....
- Cosmological constantCosmological constantIn physical cosmology, the cosmological constant was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe...
- Dark EnergyDark energyIn physical cosmology, astronomy and celestial mechanics, dark energy is a hypothetical form of energy that permeates all of space and tends to accelerate the expansion of the universe. Dark energy is the most accepted theory to explain recent observations that the universe appears to be expanding...
- Clusters of galaxies
External links
- http://pole.uchicago.edu/
- http://cosmology.berkeley.edu/group/swlh/sp_telescope/
- Life at the South Pole - Blog of Keith Vanderlinde, who operated the telescope during the 2008 season