Radio astronomy

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The Karl G. Jansky Very Large Array, a radio interferometer in New Mexico, United States USA.NM.VeryLargeArray.02.jpg
The Karl G. Jansky Very Large Array, a radio interferometer in New Mexico, United States

Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an astronomical object was in 1933, when Karl Jansky at Bell Telephone Laboratories reported radiation coming from the Milky Way. Subsequent observations have identified a number of different sources of radio emission. These include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the cosmic microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy.

Contents

Radio astronomy is conducted using large radio antennas referred to as radio telescopes, that are either used singularly, or with multiple linked telescopes utilizing the techniques of radio interferometry and aperture synthesis. The use of interferometry allows radio astronomy to achieve high angular resolution, as the resolving power of an interferometer is set by the distance between its components, rather than the size of its components.

Radio astronomy differs from radar astronomy in that the former is a passive observation (i.e., receiving only) and the latter an active one (transmitting and receiving).

History

Karl Jansky and his rotating directional antenna (early 1930s) in Holmdel, New Jersey, the world's first radio telescope, which was used to discover radio emissions from the Milky Way JanskyatAntenna hi.tif
Karl Jansky and his rotating directional antenna (early 1930s) in Holmdel, New Jersey, the world's first radio telescope, which was used to discover radio emissions from the Milky Way

Before Jansky observed the Milky Way in the 1930s, physicists speculated that radio waves could be observed from astronomical sources. In the 1860s, James Clerk Maxwell's equations had shown that electromagnetic radiation is associated with electricity and magnetism, and could exist at any wavelength. Several attempts were made to detect radio emission from the Sun including an experiment by German astrophysicists Johannes Wilsing and Julius Scheiner in 1896 and a centimeter wave radiation apparatus set up by Oliver Lodge between 1897 and 1900. These attempts were unable to detect any emission due to technical limitations of the instruments. The discovery of the radio reflecting ionosphere in 1902, led physicists to conclude that the layer would bounce any astronomical radio transmission back into space, making them undetectable. [1]

Karl Jansky made the discovery of the first astronomical radio source serendipitously in the early 1930s. As a newly hired radio engineer with Bell Telephone Laboratories, he was assigned the task to investigate static that might interfere with short wave transatlantic voice transmissions. Using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a persistent repeating signal or "hiss" of unknown origin. Since the signal peaked about every 24 hours, Jansky first suspected the source of the interference was the Sun crossing the view of his directional antenna. Continued analysis, however, showed that the source was not following the 24-hour daily cycle of the Sun exactly, but instead repeating on a cycle of 23 hours and 56 minutes. Jansky discussed the puzzling phenomena with his friend, astrophysicist Albert Melvin Skellett, who pointed out that the observed time between the signal peaks was the exact length of a sidereal day; the time it took for "fixed" astronomical objects, such as a star, to pass in front of the antenna every time the Earth rotated. [2] By comparing his observations with optical astronomical maps, Jansky eventually concluded that the radiation source peaked when his antenna was aimed at the densest part of the Milky Way in the constellation of Sagittarius. [3]

Jansky announced his discovery at a meeting in Washington, D.C., in April 1933 and the field of radio astronomy was born. [4] In October 1933, his discovery was published in a journal article entitled "Electrical disturbances apparently of extraterrestrial origin" in the Proceedings of the Institute of Radio Engineers . [5] Jansky concluded that since the Sun (and therefore other stars) were not large emitters of radio noise, the strange radio interference may be generated by interstellar gas and dust in the galaxy, in particular, by "thermal agitation of charged particles." [2] [6] (Jansky's peak radio source, one of the brightest in the sky, was designated Sagittarius A in the 1950s and was later hypothesized to be emitted by electrons in a strong magnetic field. Current thinking is that these are ions in orbit around a massive Black hole at the center of the galaxy at a point now designated as Sagittarius A*. The asterisk indicates that the particles at Sagittarius A are ionized.) [7] [8] [9] [10]

After 1935, Jansky wanted to investigate the radio waves from the Milky Way in further detail, but Bell Labs reassigned him to another project, so he did no further work in the field of astronomy. His pioneering efforts in the field of radio astronomy have been recognized by the naming of the fundamental unit of flux density, the jansky (Jy), after him. [11]

Grote Reber's Antenna at Wheaton, Illinois, world's first parabolic radio telescope Grote Antenna Wheaton.gif
Grote Reber's Antenna at Wheaton, Illinois, world's first parabolic radio telescope

Grote Reber was inspired by Jansky's work, and built a parabolic radio telescope 9m in diameter in his backyard in 1937. He began by repeating Jansky's observations, and then conducted the first sky survey in the radio frequencies. [12] On February 27, 1942, James Stanley Hey, a British Army research officer, made the first detection of radio waves emitted by the Sun. [13] Later that year George Clark Southworth, [14] at Bell Labs like Jansky, also detected radiowaves from the Sun. Both researchers were bound by wartime security surrounding radar, so Reber, who was not, published his 1944 findings first. [15] Several other people independently discovered solar radio waves, including E. Schott in Denmark [16] and Elizabeth Alexander working on Norfolk Island. [17] [18] [19] [20]

Chart on which Jocelyn Bell Burnell first recognised evidence of a pulsar, in 1967 (exhibited at Cambridge University Library) Chart Showing Radio Signal of First Identified Pulsar.jpg
Chart on which Jocelyn Bell Burnell first recognised evidence of a pulsar, in 1967 (exhibited at Cambridge University Library)

At Cambridge University, where ionospheric research had taken place during World War II, J. A. Ratcliffe along with other members of the Telecommunications Research Establishment that had carried out wartime research into radar, created a radiophysics group at the university where radio wave emissions from the Sun were observed and studied. This early research soon branched out into the observation of other celestial radio sources and interferometry techniques were pioneered to isolate the angular source of the detected emissions. Martin Ryle and Antony Hewish at the Cavendish Astrophysics Group developed the technique of Earth-rotation aperture synthesis. The radio astronomy group in Cambridge went on to found the Mullard Radio Astronomy Observatory near Cambridge in the 1950s. During the late 1960s and early 1970s, as computers (such as the Titan) became capable of handling the computationally intensive Fourier transform inversions required, they used aperture synthesis to create a 'One-Mile' and later a '5 km' effective aperture using the One-Mile and Ryle telescopes, respectively. They used the Cambridge Interferometer to map the radio sky, producing the Second (2C) and Third (3C) Cambridge Catalogues of Radio Sources. [21]

Techniques

Window of radio waves observable from Earth, on rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation Atmospheric electromagnetic opacity.svg
Window of radio waves observable from Earth, on rough plot of Earth's atmospheric absorption and scattering (or opacity) of various wavelengths of electromagnetic radiation

Radio astronomers use different techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze its emission. To "image" a region of the sky in more detail, multiple overlapping scans can be recorded and pieced together in a mosaic image. The type of instrument used depends on the strength of the signal and the amount of detail needed.

Observations from the Earth's surface are limited to wavelengths that can pass through the atmosphere. At low frequencies or long wavelengths, transmission is limited by the ionosphere, which reflects waves with frequencies less than its characteristic plasma frequency. Water vapor interferes with radio astronomy at higher frequencies, which has led to building radio observatories that conduct observations at millimeter wavelengths at very high and dry sites, in order to minimize the water vapor content in the line of sight. Finally, transmitting devices on Earth may cause radio-frequency interference. Because of this, many radio observatories are built at remote places.

Radio telescopes

Radio telescopes may need to be extremely large in order to receive signals with low signal-to-noise ratio. Also since angular resolution is a function of the diameter of the "objective" in proportion to the wavelength of the electromagnetic radiation being observed, radio telescopes have to be much larger in comparison to their optical counterparts. For example, a 1-meter diameter optical telescope is two million times bigger than the wavelength of light observed giving it a resolution of roughly 0.3 arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, only be able to resolve an object the size of the full moon (30 minutes of arc).

Radio interferometry

The Atacama Large Millimeter Array (ALMA), many antennas linked together in a radio interferometer The Atacama Compact Array.jpg
The Atacama Large Millimeter Array (ALMA), many antennas linked together in a radio interferometer
M87 optical image.jpg
An optical image of the galaxy M87 (HST), a radio image of same galaxy using Interferometry (Very Large Array - VLA), and an image of the center section (VLBA) using a Very Long Baseline Array (Global VLBI) consisting of antennas in the US, Germany, Italy, Finland, Sweden and Spain. The jet of particles is suspected to be powered by a black hole in the center of the galaxy. M87 VLA VLBA radio astronomy.jpg
An optical image of the galaxy M87 (HST), a radio image of same galaxy using Interferometry (Very Large ArrayVLA), and an image of the center section (VLBA) using a Very Long Baseline Array (Global VLBI) consisting of antennas in the US, Germany, Italy, Finland, Sweden and Spain. The jet of particles is suspected to be powered by a black hole in the center of the galaxy.

The difficulty in achieving high resolutions with single radio telescopes led to radio interferometry, developed by British radio astronomer Martin Ryle and Australian engineer, radiophysicist, and radio astronomer Joseph Lade Pawsey and Ruby Payne-Scott in 1946. The first use of a radio interferometer for an astronomical observation was carried out by Payne-Scott, Pawsey and Lindsay McCready on 26 January 1946 using a single converted radar antenna (broadside array) at 200 MHz near Sydney, Australia. This group used the principle of a sea-cliff interferometer in which the antenna (formerly a World War II radar) observed the Sun at sunrise with interference arising from the direct radiation from the Sun and the reflected radiation from the sea. With this baseline of almost 200 meters, the authors determined that the solar radiation during the burst phase was much smaller than the solar disk and arose from a region associated with a large sunspot group. The Australia group laid out the principles of aperture synthesis in a ground-breaking paper published in 1947. The use of a sea-cliff interferometer had been demonstrated by numerous groups in Australia, Iran and the UK during World War II, who had observed interference fringes (the direct radar return radiation and the reflected signal from the sea) from incoming aircraft.

The Cambridge group of Ryle and Vonberg observed the Sun at 175 MHz for the first time in mid July 1946 with a Michelson interferometer consisting of two radio antennas with spacings of some tens of meters up to 240 meters. They showed that the radio radiation was smaller than 10 arc minutes in size and also detected circular polarization in the Type I bursts. Two other groups had also detected circular polarization at about the same time (David Martyn in Australia and Edward Appleton with James Stanley Hey in the UK).

Modern radio interferometers consist of widely separated radio telescopes observing the same object that are connected together using coaxial cable, waveguide, optical fiber, or other type of transmission line. This not only increases the total signal collected, it can also be used in a process called aperture synthesis to vastly increase resolution. This technique works by superposing ("interfering") the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is the size of the antennas furthest apart in the array. In order to produce a high quality image, a large number of different separations between different telescopes are required (the projected separation between any two telescopes as seen from the radio source is called a "baseline") – as many different baselines as possible are required in order to get a good quality image. For example, the Very Large Array has 27 telescopes giving 351 independent baselines at once.

Very-long-baseline interferometry

Beginning in the 1970s, improvements in the stability of radio telescope receivers permitted telescopes from all over the world (and even in Earth orbit) to be combined to perform very-long-baseline interferometry. Instead of physically connecting the antennas, data received at each antenna is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. At that later time, the data is correlated with data from other antennas similarly recorded, to produce the resulting image. Using this method it is possible to synthesise an antenna that is effectively the size of the Earth. The large distances between the telescopes enable very high angular resolutions to be achieved, much greater in fact than in any other field of astronomy. At the highest frequencies, synthesised beams less than 1 milliarcsecond are possible.

The pre-eminent VLBI arrays operating today are the Very Long Baseline Array (with telescopes located across North America) and the European VLBI Network (telescopes in Europe, China, South Africa and Puerto Rico). Each array usually operates separately, but occasional projects are observed together producing increased sensitivity. This is referred to as Global VLBI. There are also a VLBI networks, operating in Australia and New Zealand called the LBA (Long Baseline Array), [22] and arrays in Japan, China and South Korea which observe together to form the East-Asian VLBI Network (EAVN). [23]

Since its inception, recording data onto hard media was the only way to bring the data recorded at each telescope together for later correlation. However, the availability today of worldwide, high-bandwidth networks makes it possible to do VLBI in real time. This technique (referred to as e-VLBI) was originally pioneered in Japan, and more recently adopted in Australia and in Europe by the EVN (European VLBI Network) who perform an increasing number of scientific e-VLBI projects per year. [24]

Astronomical sources

A radio image of the central region of the Milky Way galaxy. The arrow indicates a supernova remnant which is the location of a newly discovered transient, bursting low-frequency radio source GCRT J1745-3009. GCRT J1745-3009 2.jpg
A radio image of the central region of the Milky Way galaxy. The arrow indicates a supernova remnant which is the location of a newly discovered transient, bursting low-frequency radio source GCRT J1745-3009.

Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars [25] and radio galaxies. This is because radio astronomy allows us to see things that are not detectable in optical astronomy. Such objects represent some of the most extreme and energetic physical processes in the universe.

The cosmic microwave background radiation was also first detected using radio telescopes. However, radio telescopes have also been used to investigate objects much closer to home, including observations of the Sun and solar activity, and radar mapping of the planets.

Other sources include:

International regulation

Antenna 70 m of the Goldstone Deep Space Communications Complex, California Goldstone DSN antenna.jpg
Antenna 70 m of the Goldstone Deep Space Communications Complex, California
Antenna 110m of the Green Bank radio telescope, US Green Bank Telescope.jpg
Antenna 110m of the Green Bank radio telescope, US
Jupiter radio-bursts

Radio astronomy service (also: radio astronomy radiocommunication service) is, according to Article 1.58 of the International Telecommunication Union's (ITU) Radio Regulations (RR), [27] defined as "A radiocommunication service involving the use of radio astronomy". Subject of this radiocommunication service is to receive radio waves transmitted by astronomical or celestial objects.

Frequency allocation

The allocation of radio frequencies is provided according to Article 5 of the ITU Radio Regulations (edition 2012). [28]

In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which is with-in the responsibility of the appropriate national administration. The allocation might be primary, secondary, exclusive, and shared.

In line to the appropriate ITU Region the frequency bands are allocated (primary or secondary) to the radio astronomy service as follows.

Allocation to services
     Region 1          Region 2          Region 3     
13 360–13 410 kHz  FIXED
     RADIO ASTRONOMY
25 550–25 650         RADIO ASTRONOMY
37.5–38.25 MHz  FIXED
MOBILE
Radio astronomy
322–328.6    FIXED
MOBILE
RADIO ASTRONOMY
406.1–410    FIXED
MOBILE except aeronautical mobile
RADIO ASTRONOMY
1 400–1 427   EARTH EXPLORATION-SATELLITE (passive)
RADIO ASTRONOMY
SPACE RESEARCH (passive)
1 610.6–1 613.8

MOBILE-SATELLITE

(Earth-to-space)

RADIO ASTRONOMY
AERONAUTICAL

RADIONAVIGATION



1 610.6–1 613.8

MOBILE-SATELLITE

(Earth-to-space)

RADIO ASTRONOMY
AERONAUTICAL

RADIONAVIGATION

RADIODETERMINATION-

SATELLITE (Earth-to-space)
1 610.6–1 613.8

MOBILE-SATELLITE

(Earth-to-space)

RADIO ASTRONOMY
AERONAUTICAL

RADIONAVIGATION

Radiodetermination-

satellite (Earth-to-space)
10.6–10.68 GHz RADIO ASTRONOMY and other services
10.68–10.7          RADIO ASTRONOMY and other services
14.47–14.5          RADIO ASTRONOMY and other services
15.35–15.4          RADIO ASTRONOMY and other services
22.21–22.5          RADIO ASTRONOMY and other services
23.6–24              RADIO ASTRONOMY and other services
31.3–31.5           RADIO ASTRONOMY and other services

See also

Related Research Articles

Cosmic noise, also known as galactic radio noise, is not actually sound, but a physical phenomenon derived from outside of the Earth's atmosphere. It can be detected through a radio receiver, which is an electronic device that receives radio waves and converts the information given by them to an audible form. Its characteristics are comparable to those of thermal noise. Cosmic noise occurs at frequencies above about 15 MHz when highly directional antennas are pointed toward the Sun or other regions of the sky, such as the center of the Milky Way Galaxy. Celestial objects like quasars, which are super dense objects far from Earth, emit electromagnetic waves in their full spectrum, including radio waves. The fall of a meteorite can also be heard through a radio receiver; the falling object burns from friction with the Earth's atmosphere, ionizing surrounding gases and producing radio waves. Cosmic microwave background radiation (CMBR) from outer space is also a form of cosmic noise. CMBR is thought to be a relic of the Big Bang, and pervades the space almost homogeneously over the entire celestial sphere. The bandwidth of the CMBR is wide, though the peak is in the microwave range.

<span class="mw-page-title-main">Radio telescope</span> Directional radio antenna used in radio astronomy

A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency portion of the electromagnetic spectrum emitted by astronomical objects, just as optical telescopes are the main observing instrument used in traditional optical astronomy which studies the light wave portion of the spectrum coming from astronomical objects. Unlike optical telescopes, radio telescopes can be used in the daytime as well as at night.

Infrared astronomy is a sub-discipline of astronomy which specializes in the observation and analysis of astronomical objects using infrared (IR) radiation. The wavelength of infrared light ranges from 0.75 to 300 micrometers, and falls in between visible radiation, which ranges from 380 to 750 nanometers, and submillimeter waves.

<span class="mw-page-title-main">Karl Guthe Jansky</span> American physicist and radio engineer

Karl Guthe Jansky was an American physicist and radio engineer who in April 1933 first announced his discovery of radio waves emanating from the Milky Way in the constellation Sagittarius. He is considered one of the founding figures of radio astronomy.

<span class="mw-page-title-main">Very-long-baseline interferometry</span> Comparing widely separated telescope wavefronts

Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy. In VLBI a signal from an astronomical radio source, such as a quasar, is collected at multiple radio telescopes on Earth or in space. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.

<span class="mw-page-title-main">Very Large Array</span> Radio astronomy observatory in New Mexico, US

The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory in the southwestern United States. It lies in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, approximately 50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes deployed in a Y-shaped array and all the equipment, instrumentation, and computing power to function as an interferometer. Each of the massive telescopes is mounted on double parallel railroad tracks, so the radius and density of the array can be transformed to adjust the balance between its angular resolution and its surface brightness sensitivity. Astronomers using the VLA have made key observations of black holes and protoplanetary disks around young stars, discovered magnetic filaments and traced complex gas motions at the Milky Way's center, probed the Universe's cosmological parameters, and provided new knowledge about the physical mechanisms that produce radio emission.

<span class="mw-page-title-main">Astronomical spectroscopy</span> Study of astronomy using spectroscopy to measure the spectrum of electromagnetic radiation

Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light, ultraviolet, X-ray, infrared and radio waves that radiate from stars and other celestial objects. A stellar spectrum can reveal many properties of stars, such as their chemical composition, temperature, density, mass, distance and luminosity. Spectroscopy can show the velocity of motion towards or away from the observer by measuring the Doppler shift. Spectroscopy is also used to study the physical properties of many other types of celestial objects such as planets, nebulae, galaxies, and active galactic nuclei.

<span class="mw-page-title-main">Observational astronomy</span> Division of 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 models. It is the practice and study of observing celestial objects with the use of telescopes and other astronomical instruments.

<span class="mw-page-title-main">John Gatenby Bolton</span> British-Australian astronomer

John Gatenby Bolton was a British-Australian astronomer who was fundamental to the development of radio astronomy. In particular, Bolton was integral in establishing that discrete radio sources were either galaxies or the remnants of supernovae, rather than stars. He also played a significant role in the discovery of quasars and the centre of the Milky Way. Bolton served as the inaugural director of the Parkes radio telescope in Australia and established the Owens Valley Radio Observatory in California. Bolton's students held directorships at most of the radio observatories in the world and one was a Nobel Prize winner. Bolton is considered a key figure in the development of astronomy in Australia.

Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection. At each separation and orientation, the lobe-pattern of the interferometer produces an output which is one component of the Fourier transform of the spatial distribution of the brightness of the observed object. The image of the source is produced from these measurements. Astronomical interferometers are commonly used for high-resolution optical, infrared, submillimetre and radio astronomy observations. For example, the Event Horizon Telescope project derived the first image of a black hole using aperture synthesis.

<span class="mw-page-title-main">Submillimeter Array</span> Astronomical radio interferometer in Hawaii, USA

The Submillimeter Array (SMA) consists of eight 6-meter (20 ft) diameter radio telescopes arranged as an interferometer for submillimeter wavelength observations. It is the first purpose-built submillimeter interferometer, constructed after successful interferometry experiments using the pre-existing 15-meter (49 ft) James Clerk Maxwell Telescope and 10.4-meter (34.1 ft) Caltech Submillimeter Observatory as an interferometer. All three of these observatories are located at Mauna Kea Observatory on Mauna Kea, Hawaii, and have been operated together as a ten element interferometer in the 230 and 345 GHz bands. The baseline lengths presently in use range from 16 to 508 meters. The radio frequencies accessible to this telescope range from 194–408 gigahertz (1.545–0.735 mm) which includes rotational transitions of dozens of molecular species as well as continuum emission from interstellar dust grains. Although the array is capable of operating both day and night, most of the observations take place at nighttime when the atmospheric phase stability is best.

<span class="mw-page-title-main">Submillimetre astronomy</span> Astronomy with terahertz (< 1 mm)-range light

Submillimetre astronomy or submillimeter astronomy is the branch of observational astronomy that is conducted at submillimetre wavelengths of the electromagnetic spectrum. Astronomers place the submillimetre waveband between the far-infrared and microwave wavebands, typically taken to be between a few hundred micrometres and a millimetre. It is still common in submillimetre astronomy to quote wavelengths in 'microns', the old name for micrometre.

<span class="mw-page-title-main">Haystack Observatory</span> American microwave observatory owned by MIT

Haystack Observatory is a multidisciplinary radio science center, ionospheric observatory, and astronomical microwave observatory owned by Massachusetts Institute of Technology (MIT). It is in Westford, Massachusetts, in the United States, about 45 kilometers (28 mi) northwest of Boston. The observatory was built by MIT's Lincoln Laboratory for the United States Air Force and was called the Haystack Microwave Research Facility. Construction began in 1960, and the antenna began operating in 1964. In 1970 the facility was transferred to MIT, which then formed the Northeast Radio Observatory Corporation (NEROC) with other universities to operate the site as the Haystack Observatory. As of January 2012, a total of nine institutions participated in NEROC.

<span class="mw-page-title-main">Astronomical interferometer</span> Array used for astronomical observations

An astronomical interferometer or telescope array is a set of separate telescopes, mirror segments, or radio telescope antennas that work together as a single telescope to provide higher resolution images of astronomical objects such as stars, nebulas and galaxies by means of interferometry. The advantage of this technique is that it can theoretically produce images with the angular resolution of a huge telescope with an aperture equal to the separation, called baseline, between the component telescopes. The main drawback is that it does not collect as much light as the complete instrument's mirror. Thus it is mainly useful for fine resolution of more luminous astronomical objects, such as close binary stars. Another drawback is that the maximum angular size of a detectable emission source is limited by the minimum gap between detectors in the collector array.

<span class="mw-page-title-main">Telescope</span> Instrument that makes distant objects appear magnified

A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally it was an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects – an optical telescope. Nowadays, the word "telescope" is defined as wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.

<span class="mw-page-title-main">IRAM 30m telescope</span> Radio telescope in Spain

IRAM 30m telescope is a radio telescope, located in the Sierra Nevada mountain range, Spain. It is operated by the Institute for Radio Astronomy in the Millimetre Range (IRAM) for observing astronomical objects in the millimetre range of the electromagnetic spectrum. With its large surface and wide-angle camera, the telescope is capable of exploring large cosmic objects. It is one of the largest and most sensitive millimetre wavelength telescopes in the world, serving over 200 astronomers annually. The telescope is primarily used to study interstellar clouds, star birthplaces, galaxies, and black hole jets.

In optical astronomy, interferometry is used to combine signals from two or more telescopes to obtain measurements with higher resolution than could be obtained with either telescopes individually. This technique is the basis for astronomical interferometer arrays, which can make measurements of very small astronomical objects if the telescopes are spread out over a wide area. If a large number of telescopes are used a picture can be produced which has resolution similar to a single telescope with the diameter of the combined spread of telescopes. These include radio telescope arrays such as VLA, VLBI, SMA, astronomical optical interferometer arrays such as COAST, NPOI and IOTA, resulting in the highest resolution optical images ever achieved in astronomy. The VLT Interferometer is expected to produce its first images using aperture synthesis soon, followed by other interferometers such as the CHARA array and the Magdalena Ridge Observatory Interferometer which may consist of up to 10 optical telescopes. If outrigger telescopes are built at the Keck Interferometer, it will also become capable of interferometric imaging.

<span class="mw-page-title-main">Large Latin American Millimeter Array</span>

The Large Latin American Millimeter Array (LLAMA) is a single-dish 12 m Nasmyth optics antenna which is under construction in the Puna de Atacama desert in the Province of Salta, Argentina, next to the Qubic experiment. The primary mirror accuracy will allow observation from 40 GHz up to 900 GHz. After installation it will be able to join other similar instruments to perform Very Large Base Line Interferometry or to work in standalone mode. Financial support is provided by the Argentinian and Brazilian governments. The total cost of construction, around US$20 million, and operation as well as the telescope time use will be shared equally by the two countries. Construction planning started in July 2014 after the formal signature of an agreement between the main institutions involved.

<span class="mw-page-title-main">Nançay Radio Observatory</span> Radio observatory in France

The Nançay Radio Observatory, opened in 1956, is part of Paris Observatory, and also associated with the University of Orléans. It is located in the department of Cher in the Sologne region of France. The station consists of several instruments. Most iconic of these is the large decimetric radio telescope, which is one of the largest radio telescopes in the world. Long established are also the radio heliograph, a T-shaped array, and the decametric array operating at wavelengths between 3 m and 30 m.

References

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