Radio astronomy

The Karl G. Jansky Very Large Array, a radio interferometer in New Mexico, United States
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.
Grote Reber's Antenna at Wheaton, Illinois, world's first parabolic radio telescope
Chart on which Jocelyn Bell Burnell first recognised evidence of a pulsar, in 1967 (exhibited at Cambridge University Library)
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.
The Atacama Large Millimeter Array (ALMA), many antennas linked together in a radio interferometer
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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.
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.
Antenna 70 m of the Goldstone Deep Space Communications Complex, California
Antenna 110m of the Green Bank radio telescope, USA

Subfield of astronomy that studies celestial objects at radio frequencies.

- Radio astronomy
The Karl G. Jansky Very Large Array, a radio interferometer in New Mexico, United States

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Karl Guthe Jansky

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.

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.

Jansky and his rotating directional radio antenna (early 1930s), the world's first radio telescope.
Karl G. Jansky Very Large Array, National Radio Astronomy Observatory, New Mexico
Full-size replica of Jansky's radio telescope, now at the Green Bank Observatory
Green Banks plaque: Jansky Antenna

He is considered one of the founding figures of radio astronomy.

Artist's rendering of the accretion disc in ULAS J1120+0641, a very distant quasar powered by a supermassive black hole with a mass two billion times that of the Sun

Quasar

Extremely luminous active galactic nucleus (AGN), powered by a supermassive black hole, with mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc.

Extremely luminous active galactic nucleus (AGN), powered by a supermassive black hole, with mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc.

Artist's rendering of the accretion disc in ULAS J1120+0641, a very distant quasar powered by a supermassive black hole with a mass two billion times that of the Sun
Sloan Digital Sky Survey image of quasar 3C 273, illustrating the object's star-like appearance. The quasar's jet can be seen extending downward and to the right from the quasar.
Hubble images of quasar 3C 273. At right, a coronagraph is used to block the quasar's light, making it easier to detect the surrounding host galaxy.
A cosmic mirage known as the Einstein Cross. Four apparent images are actually from the same quasar.
Cloud of gas around the distant quasar SDSS J102009.99+104002.7, taken by MUSE
Quasars in interacting galaxies
Bright halos around 18 distant quasars
The Chandra X-ray image is of the quasar PKS 1127-145, a highly luminous source of X-rays and visible light about 10 billion light-years from Earth. An enormous X-ray jet extends at least a million light-years from the quasar. Image is 60 arcseconds on a side. RA 11h 30m 7.10s Dec −14° 49' 27" in Crater. Observation date: May 28, 2000. Instrument: ACIS
Gravitationally lensed quasar HE 1104-1805
This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination.
Spectrum from quasar HE 0940-1050 after it has travelled through intergalactic medium
The energetic radiation of the quasar makes dark galaxies glow, helping astronomers to understand the obscure early stages of galaxy formation.
Illustration of Double Quasars in Merging Galaxies<ref>{{cite web|title=Black Hole Pairs Found in Distant Merging Galaxies|url=https://noirlab.edu/public/news/noirlab2113/|access-date=April 9, 2021}}</ref>
These two NASA/ESA Hubble Space Telescope images reveal two pairs of quasars that existed 10 billion years ago and reside at the hearts of merging galaxies.<ref>{{cite web|title=Hubble Resolves Two Pairs of Quasars|url=https://esahubble.org/images/opo2114a/|access-date=April 13, 2021}}</ref>

But when radio astronomy began in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation.

ESO’s VLT interferometer took the first detailed image of a disc around a young star.

Astronomical interferometer

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.

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.

ESO’s VLT interferometer took the first detailed image of a disc around a young star.
A 20-foot Michelson interferometer mounted on the frame of the 100-inch Hooker Telescope, 1920.
Aerial view of the ESO/NAOJ/NRAO ALMA construction site.
The Navy Precision Optical Interferometer (NPOI), a 437 ma baselined optical/near-infrared, 6-beam Michelson Interferometer at 2163 m elevation on Anderson Mesa in Northern Arizona, USA. Four additional 1.8-meter telescopes are being installed starting from 2013.
Light collected by three ESO VLT auxiliary telescopes, and combined using the technique of interferometry.
This image shows one of a series of sophisticated optical and mechanical systems called star separators for the Very Large Telescope Interferometer (VLTI).
Two of the Atacama Large Millimeter/submillimeter array (ALMA) 12-metre antennas gaze at the sky at the observatory's Array Operations Site (AOS), high on the Chajnantor plateau at an altitude of 5000 metres in the Chilean Andes.

Interferometry is most widely used in radio astronomy, in which signals from separate radio telescopes are combined.

Bell Labs

Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),

Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984),

Bell's 1893 Volta Bureau building in Washington, D.C.
The original home of Bell Laboratories beginning in 1925, 463 West Street, New York.
Old Bell Labs Holmdel Complex. Located in New Jersey, about 20 miles south of New York.
Bell Laboratories logo, used from 1969 until 1983
Reconstruction of the directional antenna used in the discovery of radio emission of extraterrestrial origin by Karl Guthe Jansky at Bell Telephone Laboratories in 1932
The first transistor, a point-contact germanium device, was invented at Bell Laboratories in 1947. This image shows a replica.
The charge-coupled device was invented by George E. Smith and Willard Boyle
The C programming language was developed in 1972.
Bell Laboratories logo, used from 1984 until 1995
Lucent Logo bearing the "Bell Labs Innovations" tagline
Pre-2013 logo of Alcatel-Lucent, parent company of Bell Labs
Nokia Bell Labs entrance sign at New Jersey headquarters in 2016

Researchers working at Bell Laboratories are credited with the development of radio astronomy, the transistor, the laser, the photovoltaic cell, the charge-coupled device (CCD), information theory, the Unix operating system, and the programming languages B, C, C++, S, SNOBOL, AWK, AMPL, and others.

Most aperture synthesis interferometers use the rotation of the Earth to increase the number of baseline orientations included in an observation. In this example with the Earth represented as a grey sphere, the baseline between telescope A and telescope B changes angle with time as viewed from the radio source as the Earth rotates. Taking data at different times thus provides measurements with different telescope separations.

Aperture synthesis

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.

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.

Most aperture synthesis interferometers use the rotation of the Earth to increase the number of baseline orientations included in an observation. In this example with the Earth represented as a grey sphere, the baseline between telescope A and telescope B changes angle with time as viewed from the radio source as the Earth rotates. Taking data at different times thus provides measurements with different telescope separations.

Astronomical interferometers are commonly used for high-resolution optical, infrared, submillimetre and radio astronomy observations.

Electromagnetic interference in analog TV signal

Electromagnetic interference

Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.

Disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrostatic coupling, or conduction.

Electromagnetic interference in analog TV signal
Interference by 5 GHz Wi-Fi seen on Doppler weather radar

It can also affect mobile phones, FM radios, and televisions, as well as observations for radio astronomy and atmospheric science.

One of the two known surviving sidereal angle clocks in the world, made by John Arnold & Son. It was previously owned by Sir George Shuckburgh-Evelyn. It is on display in the Royal Observatory, Greenwich, London.

Sidereal time

Timekeeping system that astronomers use to locate celestial objects.

Timekeeping system that astronomers use to locate celestial objects.

One of the two known surviving sidereal angle clocks in the world, made by John Arnold & Son. It was previously owned by Sir George Shuckburgh-Evelyn. It is on display in the Royal Observatory, Greenwich, London.
Sidereal time vs solar time. Above left: a distant star (the small orange star) and the Sun are at culmination, on the local meridian m. Centre: only the distant star is at culmination (a mean sidereal day). Right: a few minutes later the Sun is on the local meridian again. A solar day is complete.
Photo of the face of the other surviving Sidereal Angle clock in the Royal Observatory in Greenwich, England, made by Thomas Tompion. The dial has been ornately inscribed with the name J Flamsteed, who was the Astronomer Royal, and the date 1691.
This astronomical clock uses dials showing both sidereal and solar time.

Beginning in the 1970s the radio astronomy methods very long baseline interferometry (VLBI) and pulsar timing overtook optical instruments for the most precise astrometry.

The 64-meter radio telescope at Parkes Observatory as seen in 1969, when it was used to receive live televised video from Apollo 11

Radio telescope

Specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky.

Specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky.

The 64-meter radio telescope at Parkes Observatory as seen in 1969, when it was used to receive live televised video from Apollo 11
Antenna of UTR-2 low frequency radio telescope, Kharkiv region, Ukraine. Consists of an array of 2040 cage dipole elements.
Ooty radio telescope, a 326.5 MHz dipole array in Ooty, India
Plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation.
The Very Large Array in Socorro, New Mexico, an interferometric array formed of 27 parabolic dish telescopes.
Atacama Large Millimeter Array in the Atacama desert consisting of 66 12-metre (39 ft), and 7-metre (23 ft) diameter radio telescopes designed to work at sub-millimeter wavelengths
alt=Five hundred meter Aperture Spherical Telescope under construction|The 500 meter Five hundred meter Aperture Spherical Telescope (FAST), under construction, China (2016)
alt=Green Bank Telescope|The 100 meter Green Bank Telescope, Green Bank, West Virginia, US, the largest fully steerable radio telescope dish (2002)
alt=Effelsberg 100-m Radio Telescope|The 100 meter Effelsberg, in Bad Münstereifel, Germany (1971)
alt=Lovell Telescope|The 76 meter Lovell, Jodrell Bank Observatory, England (1957)
alt=DSS 14 "Mars" antenna at Goldstone Deep Space Communications Complex|The 70 meter DSS 14 "Mars" antenna at Goldstone Deep Space Communications Complex, Mojave Desert, California, US (1958)
alt=Yevpatoria RT-70 radio telescope|The 70 meter Yevpatoria RT-70, Crimea, first of three RT-70 in the former Soviet Union, (1978)
The 70 meter Galenki RT-70, Galenki, Russia, second of three RT-70 in the former Soviet Union, (1984)

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.

Some of the Atacama Large Millimeter Array radio telescopes.

Very-long-baseline interferometry

Some of the Atacama Large Millimeter Array radio telescopes.
The eight radio telescopes of the Smithsonian Submillimeter Array, located at the Mauna Kea Observatory in Hawai'i.
VLBI was used to create the first image of a black hole, imaged by the Event Horizon Telescope and published in April 2019.
Recording data at each of the telescopes in a VLBI array. Extremely accurate high-frequency clocks are recorded alongside the astronomical data in order to help get the synchronization correct
Playing back the data from each of the telescopes in a VLBI array. Great care must be taken to synchronize the play back of the data from different telescopes. Atomic clock signals recorded with the data help in getting the timing correct.
Image of the source IRC+10420. The lower resolution image on the left image was taken with the UK's MERLIN array and shows the shell of maser emission produced by an expanding shell of gas with a diameter about 200 times that of the Solar System. The shell of gas was ejected from a supergiant star (10 times the mass of our sun) at the centre of the emission about 900 years ago. The corresponding EVN e-VLBI image (right) shows the much finer structure of the masers because of the higher resolution of the VLBI array.

Very-long-baseline interferometry (VLBI) is a type of astronomical interferometry used in radio astronomy.

One of the 28 radio telescopes undergoing maintenance in "The Barn"

Very Large Array

One of the 28 radio telescopes undergoing maintenance in "The Barn"
The Bracewell Radio Sundial on the VLA walking tour, seen from the south. Named for Ronald N. Bracewell, this sundial marks on the ground positions of the shadow of the central sphere (the gnomon) at different times of day and times of year. The shadow on Dec 22, 2017 falls very near the winter solstice line and the 1:00 PM (solar time) mark. The other two lines of markers north of the gnomon are for the equinoxes and the summer solstice. Additional lines of markers south of the gnomon mark positions of "shadows" of the radio sources Cygnus A and Cassiopeia A. The posts at the back of the sundial were recovered from Bracewell's radio telescope array at Stanford University, abandoned in 1980, where they had been signed by visitors with chisels at his invitation.

The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 mi west of Socorro.