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. The Very Large Array ( VLA) is a Radio astronomy Observatory located on the Plains of San Augustin, between the towns of Magdalena Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of New Mexico ( is a state located in the southwestern region of the United States of America. The United States of America —commonly referred to as the Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study s are significant physical entities, associations or structures which current Science has confirmed to exist in Space. Radio frequency ( RF) is a Frequency or rate of Oscillation within the range of about 3 Hz to 300 GHz The electromagnetic (EM spectrum is the range of all possible Electromagnetic radiation frequencies Radio astronomy techniques are similar to optical techniques but radio telescopes have to be much larger due to the longer wavelengths being observed. An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites The field originated from the discovery that most astronomical objects emit radiation in the radio wavelengths as well as optical ones.

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. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric Several notable scientists and experimenters such as Thomas Edison, Oliver Lodge, and Max Planck predicted that the sun should be emitting radio waves. Sir Oliver Joseph Lodge, FRS ( June 12, 1851 - August 22, 1940) born at Penkhull in Stoke-on-Trent and educated Lodge tried to observe solar signals but was unable to detect them due to technical limitations of his apparatus^[1].

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. Serendipity is the effect by which one accidentally discovers something fortunate especially while looking for something else entirely Karl Guthe Jansky ( October 22, 1905 &ndash February 14, 1950) was an American Physicist and Radio Engineer Bell Laboratories (also known as Bell Labs and formerly known as AT&T Bell Laboratories and Bell Telephone Laboratories) is the Research organization Shortwave Radio operates between the frequencies of 3000 KHz (3 Using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive An analog or analogue signal is any continuous signal for which the time varying feature (variable of the signal is a representation of some other Since the signal peaked once a day, Jansky originally suspected the source of the interference was the sun. Continued analysis showed that the source was not following the 24 hour cycle for the rising and setting of the sun 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. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox 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 of the galaxy, in the constellation of Sagittarius ^[2]. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture He announced his discovery in 1933. Year 1933 ( MCMXXXIII) was a Common year starting on Sunday (link will display full calendar of the Gregorian calendar. 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.

Grote Reber helped pioneer radio astronomy when he built a large parabolic "dish" radio telescope (9m in diameter) in 1937. Grote Reber ( December 22, 1911 &ndash December 20, 2002) was an amateur astronomer and pioneer of Radio astronomy. 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. Events 1560 - The Treaty of Berwick, which would expel the French from Scotland, is signed by England and the Congregation Year 1942 ( MCMXLII) was a Common year starting on Thursday (the link will display the full 1942 calendar of the Gregorian calendar. S. Hey, a British Army research officer, helped progress radio astronomy further, when he discovered that the sun emitted radio waves ^[4]. The British Army is the land armed forces branch of the British Armed Forces. 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. Sir Martin Ryle ( September 27, 1918 - October 14, 1984) was an English radio astronomer who developed revolutionary Antony Hewish (born Fowey, Cornwall, May 11, 1924) is a British radio astronomer who won the Nobel Prize for The University of Cambridge (often Cambridge University) located in Cambridge, England, is the second-oldest university in the The Cambridge Interferometer was a Radio telescope interferometer built by Martin Ryle and Antony Hewish in the early 1950s to the west of 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

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'). Art History Mosaics of the 4th century BC are found in the Macedonian palace-city of Aegae, and they enriched the floors of Hellenistic The types of instruments being used depends on the weakness of the signal and the amount of detail needed.

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. A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into The Very Large Array ( VLA) is a Radio astronomy Observatory located on the Plains of San Augustin, between the towns of Magdalena The jet of particles is suspected to be powered by a black hole in the center of the galaxy. A black hole is a theoretical region of space in which the Gravitational field is so powerful that nothing not even Electromagnetic radiation (e

Radio telescopes may need to be extremely large in order to receive signals with low signal-to-noise ratio. Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements 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. Angular resolution describes the resolving power of any image forming device such as an optical or Radio telescope, a Microscope, a Camera An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum 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). A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree.

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. Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of Sir Martin Ryle ( September 27, 1918 - October 14, 1984) was an English radio astronomer who developed revolutionary Joseph Lade Pawsey (May 14 1908&ndashNovember 30 1962 was an Australian born Engineer, radiophysicist and radio Astronomer. Year 1946 ( MCMXLVI) was a Common year starting on Tuesday (link will display full 1946 calendar of the Gregorian calendar. 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. A radio telescope is a form of directional Radio antenna used in Radio astronomy and in tracking and collecting data from Satellites Coaxial cable is a cable consisting of an inner conductor surrounded by a tubular insulating layer typically made from a flexible material with a high Dielectric constant, all A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length 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 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. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. The phase of an oscillation or wave is the fraction of a complete cycle corresponding to an offset in the displacement from a specified reference point at time t = 0 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. The Very Large Array ( VLA) is a Radio astronomy Observatory located on the Plains of San Augustin, between the towns of Magdalena

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. Very Long Baseline Interferometry (VLBI is a type of astronomical interferometry used in Radio astronomy. 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. An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element 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.

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

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 is a newly-discovered transient bursting low-frequency radio source which lies in the direction of the Galactic center.

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. Pulsars are highly magnetized rotating Neutron stars that emit a beam of Electromagnetic radiation in the form of radio waves A quasar (contraction of QUASi-stellAR radio source) is an extremely powerful and distant Active galactic nucleus. Radio galaxies and their relatives radio-loud Quasars and Blazars, are types of Active galaxy that are very luminous at radio wavelengths (up 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.

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. In Physics and cosmology, dark matter is hypothetical Matter that does not interact with the electromagnetic force but whose presence can be inferred from A galaxy is a massive gravitationally bound system consisting of Stars an Interstellar medium of gas and dust, and Dark matter 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. The Sun (Sol is the Star at the center of the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity.

Other sources include:

• Sun
• Sagittarius A, the galactic center of the Milky Way
• 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

See also

• History of astronomical interferometry

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". This article is about the country For a topic outline on this subject see List of basic France topics. 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