The Very Large Array, a radio interferometer in New Mexico, USA

Radio astronomy is a subfield of astronomy that studies celestial objects in the radio frequency portion of the electromagnetic spectrum. Radio astronomy techniques are similar to optical techniques but radio telescopes have to be much larger due to the longer wavelengths being observed. The field originated from the discovery that most astronomical objects emit radiation in the radio wavelengths as well as optical ones. Very Large Array at Socorro, New Mexico, USA. Photo taken by Hajor, 08. ... Very Large Array at Socorro, New Mexico, USA. Photo taken by Hajor, 08. ... The Very Large Array (VLA) is a radio astronomy observatory located on the Plains of San Augustin, between the towns of Magdalena and Datil, some fifty miles (80 km) west of Socorro, New Mexico, USA. U.S. Route 60 passes through the complex. ... It has been suggested that Optical interferometry be merged into this article or section. ... Capital Santa Fe Largest city Albuquerque Area  Ranked 5th  - Total 121,665 sq mi (315,194 km²)  - Width 342 miles (550 km)  - Length 370 miles (595 km)  - % water 0. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant Astronomy is the science of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earths atmosphere (such as auroras and cosmic background radiation). ... See also Lists of astronomical objects Category: ... It has been suggested that this article or section be merged with Radio waves. ... Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... An optical telescope is a telescope which is used to gather, and focus light, for directly viewing a magnified image, making a photograph, etc. ... In contrast to an ordinary telescope, which produces visible light images, a radio telescope sees radio waves emitted by radio sources, typically by means of a large parabolic (dish) antenna, or arrays of them. ...

History

The idea that celestial bodies may be emitting radio waves had been suspected some time before its discovery. In the 1860's James Clerk Maxwell's equations had shown that electromagnetic radiation from stellar sources could exist with any wavelength, not just optical. Several notable scientists and experimenters such as Thomas Edison, Oliver Lodge, and Max Planck predicted that the sun should be emitting radio waves. Lodge tried to observe solar signals but was unable to detect them due to technical limitations of his apparatus^[1]. James Clerk Maxwell (13 June 1831 – 5 November 1879) was a Scottish mathematician and theoretical physicist. ... In electromagnetism, Maxwells equations are a set of equations first presented as a distinct group in the later half of the nineteenth century by James Clerk Maxwell. ... Thomas Alva Edison (February 11, 1847 – October 18, 1931) was an American inventor and businessman who developed many devices which greatly influenced life around the world, including the phonograph and a long lasting light bulb. ... Vanity Fair cartoon. ... Max Karl Ernst Ludwig Planck (April 23, 1858 – October 4, 1947 in Göttingen, Germany) was a German physicist. ...

The first identified astronomical radio source was one discovered serendipitously in the early 1930s when Karl Guthe Jansky, an engineer with Bell Telephone Laboratories, was investigating static that interfered with short wave transatlantic voice transmissions. Using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. Since the signal peaked once a day, Jansky original suspected the source of the interference was the sun. Continued analysis showed that the source was not following the rising and setting of the sun exactly but instead repeating on a cycle of 23 hours and 56 minutes, typical of an astronomical source "fixed" on the celestial sphere rotating in sync with sidereal time. By comparing his observations with optical astronomical maps, Jansky concluded that the radiation was coming from the Milky Way and was strongest in the direction of the center the galaxy, in the constellation of Sagittarius ^[2]. He announced his discovery in 1933. Jansky wanted to investigate the radio waves from the Milky Way in further detail but Bell Labs re-assigned Jansky to another project, so he did no further work in the field of astronomy. Look up Serendipity in Wiktionary, the free dictionary. ... Karl Guthe Jansky (October 22, 1905 – February 14, 1950), was an American physicist and radio engineer who in August 1931 first discovered radio waves emanating from the Milky Way. ... Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) was the main research and development arm of the United States Bell System. ... Shortwave radio operates between the frequencies of 3,000 kHz and 30 MHz (30,000 kHz) and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than those commonly in use at that time. ... Log-periodic dipole array A directional antenna is an antenna which transmits or receives maximum power in a particular direction. ... An analog or analogue signal is an allergy continuous in both time and amplitude. ... The celestial sphere is divided by the celestial equator. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... It has been suggested that Andromeda-Milky Way collision be merged into this article or section. ... This article or section does not adequately cite its references or sources. ... For other uses, see Sagittarius. ... 1933 (MCMXXXIII) was a common year starting on Sunday. ...

Grote Reber helped pioneer radio astronomy when he built a large parabolic "dish" radio telescope (9m in diameter) in 1937. He was instrumental in repeating Karl Guthe Jansky's pioneering but somewhat simple work, and went on to conduct the first sky survey in the radio frequencies ^[3]. On February 27, 1942, J.S. Hey, a British Army research officer, helped progress radio astronomy further, when he discovered that the sun emitted radio waves ^[4]. By the early 1950s Martin Ryle and Antony Hewish at Cambridge University had used the Cambridge Interferometer to map the radio sky, producing the famous 2C and 3C surveys of radio sources. Grote Reber (December 22, 1911 – December 20, 2002) was one of the pioneers of radio astronomy. ... February 27 is the 58th day of the year in the Gregorian calendar. ... 1942 (MCMXLII) was a common year starting on Thursday (the link is to a full 1942 calendar). ... The British Army is the land armed forces branch of the British Armed Forces. ... Sir Martin Ryle (September 27, 1918 – October 14, 1984) was a British radio astronomer who developed revolutionary radio telescope systems (see e. ... Antony Hewish (born Fowey, Cornwall, May 11, 1924) is a British radio astronomer who won the Nobel Prize for Physics in 1974 (together with fellow radio-astronomer Martin Ryle) for his work on the development of radio aperture synthesis and its role in the discovery of pulsars. ... The University of Cambridge (often Cambridge University), located in Cambridge, England, is the second-oldest university in the English-speaking world and has a reputation as one of the worlds most prestigious universities. ... The Cambridge Interferometer was a radio telescope interferometer built by Martin Ryle and Antony Hewish in the early 1950s to the west of Cambridge (between the Grange Road football ground and the current Cavendish Laboratory). ... The Second Cambridge Catalogue of Radio Sources (2C) was published in 1955 by John R Shakeshaft and colleagues. ... The Third Cambridge Catalogue of Radio Sources (3C) is an astronomical catalogue of celestial radio sources detected originally at 159 MHz, and subsequently at 178 MHz. ...

Techniques

Radio astronomers use different types of techniques to observe objects in the radio spectrum. Instruments may simply be pointed at an energetic radio source to analyze what type of emissions it makes. To “image” a region of the sky in more detail, multiple overlapping scans can be recorded and piece together in an image ('mosaicing'). The types of instruments being used depends on the weakness of the signal and the amount of detail needed. Mosaic is the art of decoration with small pieces of colored glass, stone or other material. ...

Radio telescopes

Main article: Radio telescope

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 using Very Long Baseline Interferometry (Very Long Baseline Array-VLBA) 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.

Radio telescopes may need to be extremely large in order to receive signals with large 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 a few arc seconds, whereas a radio telescope "dish" many times that size may, depending on the wavelength observed, may only be able to resolve an object the size of the full moon (30 minutes of arc). The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna most often used in radio astronomy and in tracking and collecting data from satellites and space probes (see Deep Space Network), and are also used in the SETI project. ... Image File history File linksMetadata Size of this preview: 800 × 441 pixelsFull resolution (807 × 445 pixel, file size: 43 KB, MIME type: image/jpeg)Messier 87 (M87), a giant elliptical galaxy in the Virgo Cluster as imaged in a wide field veiw from the Hubble Space Telescope (detail of center... Image File history File linksMetadata Size of this preview: 800 × 441 pixelsFull resolution (807 × 445 pixel, file size: 43 KB, MIME type: image/jpeg)Messier 87 (M87), a giant elliptical galaxy in the Virgo Cluster as imaged in a wide field veiw from the Hubble Space Telescope (detail of center... Image File history File linksMetadata Size of this preview: 427 × 599 pixelsFull resolution (812 × 1139 pixel, file size: 139 KB, MIME type: image/jpeg)A radio image of Messier 87 (M87), a giant elliptical galaxy in the Virgo Cluster by the Very Large Array (VLA), and an image of the... Image File history File linksMetadata Size of this preview: 427 × 599 pixelsFull resolution (812 × 1139 pixel, file size: 139 KB, MIME type: image/jpeg)A radio image of Messier 87 (M87), a giant elliptical galaxy in the Virgo Cluster by the Very Large Array (VLA), and an image of the... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... The Very Large Array (VLA) is a radio astronomy observatory located on the Plains of San Augustin, between the towns of Magdalena and Datil, some fifty miles (80 km) west of Socorro, New Mexico, USA. U.S. Route 60 passes through the complex. ... Simulated view of a black hole in front of the Milky Way. ... Signal-to-noise ratio (often abbreviated SNR or S/N) is an electrical engineering concept defined as the ratio of a signal power to the noise power corrupting the signal. ... Angular resolution describes the resolving power of any optical device such as a telescope, a microscope, a camera, or an eye. ... Several objective lenses on a microscope. ... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna most often used in radio astronomy and in tracking and collecting data from satellites and space probes (see Deep Space Network), and are also used in the SETI project. ... An optical telescope is a telescope which is used to gather, and focus light, for directly viewing a magnified image, making a photograph, etc. ... A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ...

Radio interferometry

The difficulty in achieving high resolutions with single radio telescopes led to radio interferometry, developed by British radio astronomer Martin Ryle and Australian-born engineer, radiophysicist, and radio astronomer Joseph Lade Pawsey in 1946. 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 combed 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. It has been suggested that Optical interferometry be merged into this article or section. ... Sir Martin Ryle (September 27, 1918 – October 14, 1984) was a British radio astronomer who developed revolutionary radio telescope systems (see e. ... Joseph Lade Pawsey (May 14, 1908–November 30, 1962) was an Australian-born engineer, radiophysicist, and radio astronomer. ... 1946 (MCMXLVI) was a common year starting on Tuesday. ... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna most often used in radio astronomy and in tracking and collecting data from satellites and space probes (see Deep Space Network), and are also used in the SETI project. ... Coaxial Cable Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer (jacket). ... Look up waveguide in Wiktionary, the free dictionary. ... Optical fibers An optical fiber (or fibre) is a glass or plastic fiber designed to guide light along its length by confining as much light as possible in a propagating form. ... A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy, such as electromagnetic waves or acoustic waves, as well as electric power transmission. ... Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ... This article is about waves in the most general scientific sense. ... This article is about waves in the most general scientific sense. ... This article is about a portion of a periodic process. ... The Very Large Array (VLA) is a radio astronomy observatory located on the Plains of San Augustin, between the towns of Magdalena and Datil, some fifty miles (80 km) west of Socorro, New Mexico, USA. U.S. Route 60 passes through the complex. ...

Very Long Baseline Interferometry

Since the 1970s telescopes from all over the world (and even in Earth orbit) have been combined to perform Very Long Baseline Interferometry. 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 create an antenna that is effectively the size of the Earth. Very Long Baseline Interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy, in which the data received at each antenna in the array is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. ... Chip-scale atomic clock unveiled by NIST An Atomic Clock is a type of clock that uses an atomic resonance frequency standard to feed its counter. ...

Using these techniques, radio telescopes are able to achieve much high angular resolution and image quality than instruments working in other wavelength band.

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.

Radio astronomy has led to substantial increases in astronomical knowledge, particularly with the discovery of several classes of new objects, including pulsars, quasars 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. Image File history File links Size of this preview: 481 × 599 pixelsFull resolution (577 × 719 pixel, file size: 271 KB, MIME type: image/jpeg)A radio image of the central region of the Milky Way galaxy. ... Image File history File links Size of this preview: 481 × 599 pixelsFull resolution (577 × 719 pixel, file size: 271 KB, MIME type: image/jpeg)A radio image of the central region of the Milky Way galaxy. ... GCRT J1745-3009 is a newly-discovered, bursting, transient radio source. ... It has been suggested that Radio pulsar be merged into this article or section. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ...

Radio astronomy is also partly responsible for the idea that dark matter is an important component of our universe; radio measurements of the rotation of galaxies suggest that there is much more mass in galaxies than has been directly observed (see Vera Rubin). 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. In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ... Vera (Cooper) Rubin (born 23 July 1928) is an astronomer who has done pioneering work on galaxy rotation rates. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ... Major features of the Solar System (not to scale; from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth and its Moon, and Mars. ...

Other sources include:

• Active galactic nuclei and pulsars have jets of charged particles which emit synchrotron radiation
• Merging galaxy clusters often show diffuse radio emission[1]
• Supernova remnants can also show diffuse radio emission
• The Cosmic microwave background is blackbody radio emission

An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... It has been suggested that Radio pulsar be merged into this article or section. ... General Electric synchrotron accelerator built in 1946, the origin of the discovery of synchrotron radiation. ... The galaxies of HCG 87, about four hundred million light-years distant. ... The Crab Nebula is an expanding cloud of gas created by the 1054 supernova. ... WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ...

See also

• History of astronomical interferometry

William Herschel knew as early as 1779 (Herschel 1805) that stars appeared much larger in telescopes than they really were but he did not know why. ...

Notes

References

• nrao.edu, How Radio Telescopes Work
• The Jet of Galaxy M87

Further reading

Journals

Books

External links

French History

• The History of the Nancay Radio Observatory - a history of French radio astronomy

History (America, Post 1930s)

• History of Radio Astronomy, National Radio Astronomy Observatory
• The History of Radio Astronomy - Haystack Observatory, MIT
• Hanes, Dave, "Physics 014: The Course Notes, Radio Astronomy". Astronomy Group and Department of Physics, Queen's University. 2000-2001.
• Reber Radio Telescope - National Park Services
• Radio Telescope Developed - a brief history from NASA Goddard Space Flight Center