In physics, redshift is a phenomenon where electromagnetic radiation from an object undergoes an increase in wavelength. Whether or not the radiation is visible, "redshift" means an increase in wavelength, equivalent to a decrease in wave frequency and photon energy, in accordance with the wave and quantum theories of light. Neither the emitted nor perceived light is red. Examples of redshifting are a gamma ray perceived as an X-ray, or visible light perceived as radio waves; the opposite of a redshift is energy increases. However, redshift is a more common term and sometimes blueshift is referred to as negative redshift. There are three main causes of red in astronomy and cosmology: Objects move apart in space; this is an example of the Doppler effect. Space itself expands; this is known as cosmological redshift. All sufficiently distant light sources show redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort spacetime and exert a force on light and other particles.
Knowledge of redshifts and blueshifts has been used to develop several terrestrial technologies such as Doppler radar and radar guns. Redshifts are seen in the spectroscopic observations of astronomical objects, its value is represented by the letter z. A special relativistic redshift formula can be used to calculate the redshift of a nearby object when spacetime is flat. However, in many contexts, such as black holes and Big Bang cosmology, redshifts must be calculated using general relativity. Special relativistic and cosmological redshifts can be understood under the umbrella of frame transformation laws. There exist other physical processes that can lead to a shift in the frequency of electromagnetic radiation, including scattering and optical effects; the history of the subject began with the development in the 19th century of wave mechanics and the exploration of phenomena associated with the Doppler effect. The effect is named after Christian Doppler, who offered the first known physical explanation for the phenomenon in 1842.
The hypothesis was tested and confirmed for sound waves by the Dutch scientist Christophorus Buys Ballot in 1845. Doppler predicted that the phenomenon should apply to all waves, in particular suggested that the varying colors of stars could be attributed to their motion with respect to the Earth. Before this was verified, however, it was found that stellar colors were due to a star's temperature, not motion. Only was Doppler vindicated by verified redshift observations; the first Doppler redshift was described by French physicist Hippolyte Fizeau in 1848, who pointed to the shift in spectral lines seen in stars as being due to the Doppler effect. The effect is sometimes called the "Doppler–Fizeau effect". In 1868, British astronomer William Huggins was the first to determine the velocity of a star moving away from the Earth by this method. In 1871, optical redshift was confirmed when the phenomenon was observed in Fraunhofer lines using solar rotation, about 0.1 Å in the red. In 1887, Vogel and Scheiner discovered the annual Doppler effect, the yearly change in the Doppler shift of stars located near the ecliptic due to the orbital velocity of the Earth.
In 1901, Aristarkh Belopolsky verified optical redshift in the laboratory using a system of rotating mirrors. The earliest occurrence of the term red-shift in print appears to be by American astronomer Walter S. Adams in 1908, in which he mentions "Two methods of investigating that nature of the nebular red-shift"; the word does not appear unhyphenated until about 1934 by Willem de Sitter indicating that up to that point its German equivalent, was more used. Beginning with observations in 1912, Vesto Slipher discovered that most spiral galaxies mostly thought to be spiral nebulae, had considerable redshifts. Slipher first reports on his measurement in the inaugural volume of the Lowell Observatory Bulletin. Three years he wrote a review in the journal Popular Astronomy. In it he states that "the early discovery that the great Andromeda spiral had the quite exceptional velocity of –300 km showed the means available, capable of investigating not only the spectra of the spirals but their velocities as well."
Slipher reported the velocities for 15 spiral nebulae spread across the entire celestial sphere, all but three having observable "positive" velocities. Subsequently, Edwin Hubble discovered an approximate relationship between the redshifts of such "nebulae" and the distances to them with the formulation of his eponymous Hubble's law; these observations corroborated Alexander Friedmann's 1922 work, in which he derived the Friedmann-Lemaître equations. They are today considered strong evidence for the Big Bang theory; the spectrum of light that comes from a single source can be measured. To determine the redshift, one searches for features in the spectrum such as absorption lines, emission lines, or other variations in light intensity. If found, these featur
Seyfert galaxies are one of the two largest groups of active galaxies, along with quasars. They have quasar-like nuclei with high surface brightnesses whose spectra reveal strong, high-ionisation emission lines, but unlike quasars, their host galaxies are detectable. Seyfert galaxies account for about 10% of all galaxies and are some of the most intensely studied objects in astronomy, as they are thought to be powered by the same phenomena that occur in quasars, although they are closer and less luminous than quasars; these galaxies have supermassive black holes at their centers which are surrounded by accretion discs of in-falling material. The accretion discs are believed to be the source of the observed ultraviolet radiation. Ultraviolet emission and absorption lines provide the best diagnostics for the composition of the surrounding material. Seen in visible light, most Seyfert galaxies look like normal spiral galaxies, but when studied under other wavelengths, it becomes clear that the luminosity of their cores is of comparable intensity to the luminosity of whole galaxies the size of the Milky Way.
Seyfert galaxies are named after Carl Seyfert, who first described this class in 1943. Seyfert galaxies were first detected in 1908 by Edward A. Fath and Vesto Slipher, who were using the Lick Observatory to look at the spectra of astronomical objects that were thought to be "spiral nebulae", they noticed that NGC 1068 showed six bright emission lines, considered unusual as most objects observed showed an absorption spectrum corresponding to stars. In 1926, Edwin Hubble looked at the emission lines of NGC 1068 and two other such "nebulae" and classified them as extragalactic objects. In 1943, Carl Keenan Seyfert discovered more galaxies similar to NGC 1068 and reported that these galaxies have bright stellar-like nuclei that produce broad emission lines. In 1944 Cygnus A was detected at 160 MHz, detection was confirmed in 1948 when it was established that it was a discrete source, its double radio structure became apparent with the use of interferometry. In the next few years, other radio sources such as supernova remnants were discovered.
By the end of the 1950s, more important characteristics of Seyfert galaxies were discovered, including the fact that their nuclei are compact, have high mass, the duration of peak nuclear emissions is short. In the 1960s and 1970s, research to further understand the properties of Seyfert galaxies was carried out. A few direct measurements of the actual sizes of Seyfert nuclei were taken, it was established that the emission lines in NGC 1068 were produced in a region over a thousand light years in diameter. Controversy existed over. Confirming estimates of the distance to Seyfert galaxies and their age were limited since their nuclei vary in brightness over a time scale of a few years. In the same time period, research had been undertaken to survey and catalogue galaxies, including Seyferts. Beginning in 1967, Benjamin Markarian published lists containing a few hundred galaxies distinguished by their strong ultraviolet emission, with measurements on the position of some of them being improved in 1973 by other researchers.
At the time, it was believed. By 1977, it was found that few Seyfert galaxies are ellipticals, most of them being spiral or barred spiral galaxies. During the same time period, efforts have been made to gather spectrophotometric data for Seyfert galaxies, it became obvious that not all spectra from Seyfert galaxies look the same, so they have been subclassified according to the characteristics of their emission spectra. A simple division into types I and II has been devised, with the classes depending on the relative width of their emission lines, it has been noticed that some Seyfert nuclei show intermediate properties, resulting in their being further subclassified into types 1.2, 1.5, 1.8 and 1.9. Early surveys for Seyfert galaxies were biased in counting only the brightest representatives of this group. More recent surveys that count galaxies with low-luminosity and obscured Seyfert nuclei suggest that the Seyfert phenomenon is quite common, occurring in 16% ± 5% of galaxies. Seyfert galaxies form a substantial fraction of the galaxies appearing in the Markarian catalog, a list of galaxies displaying an ultraviolet excess in their nuclei.
An active galactic nucleus is a compact region at the center of a galaxy that has a higher than normal luminosity over portions of the electromagnetic spectrum. A galaxy having an active nucleus is called an active galaxy. Active galactic nuclei are the most luminous sources of electromagnetic radiation in the Universe, their evolution puts constraints on cosmological models. Depending on the type, their luminosity varies over a timescale from a few hours to a few years; the two largest subclasses of active galaxies are quasars and Seyfert galaxies, the main difference between the two being the amount of radiation they emit. In a typical Seyfert galaxy, the nuclear source emits at visible wavelengths an amount of radiation comparable to that of the whole galaxy's constituent stars, while in a quasar, the nuclear source is brighter than the constituent stars by at least a factor of 100. Seyfert galaxies have bright nuclei, with luminosities ranging between 108 and 1011 solar luminosities
A constellation is a group of stars that forms an imaginary outline or pattern on the celestial sphere representing an animal, mythological person or creature, a god, or an inanimate object. The origins of the earliest constellations go back to prehistory. People used them to relate stories of their beliefs, creation, or mythology. Different cultures and countries adopted their own constellations, some of which lasted into the early 20th century before today's constellations were internationally recognized. Adoption of constellations has changed over time. Many have changed in shape; some became popular. Others were limited to single nations; the 48 traditional Western constellations are Greek. They are given in Aratus' work Phenomena and Ptolemy's Almagest, though their origin predates these works by several centuries. Constellations in the far southern sky were added from the 15th century until the mid-18th century when European explorers began traveling to the Southern Hemisphere. Twelve ancient constellations belong to the zodiac.
The origins of the zodiac remain uncertain. In 1928, the International Astronomical Union formally accepted 88 modern constellations, with contiguous boundaries that together cover the entire celestial sphere. Any given point in a celestial coordinate system lies in one of the modern constellations; some astronomical naming systems include the constellation where a given celestial object is found to convey its approximate location in the sky. The Flamsteed designation of a star, for example, consists of a number and the genitive form of the constellation name. Other star patterns or groups called asterisms are not constellations per se but are used by observers to navigate the night sky. Examples of bright asterisms include the Pleiades and Hyades within the constellation Taurus or Venus' Mirror in the constellation of Orion.. Some asterisms, like the False Cross, are split between two constellations; the word "constellation" comes from the Late Latin term cōnstellātiō, which can be translated as "set of stars".
The Ancient Greek word for constellation is ἄστρον. A more modern astronomical sense of the term "constellation" is as a recognisable pattern of stars whose appearance is associated with mythological characters or creatures, or earthbound animals, or objects, it can specifically denote the recognized 88 named constellations used today. Colloquial usage does not draw a sharp distinction between "constellations" and smaller "asterisms", yet the modern accepted astronomical constellations employ such a distinction. E.g. the Pleiades and the Hyades are both asterisms, each lies within the boundaries of the constellation of Taurus. Another example is the northern asterism known as the Big Dipper or the Plough, composed of the seven brightest stars within the area of the IAU-defined constellation of Ursa Major; the southern False Cross asterism includes portions of the constellations Carina and Vela and the Summer Triangle.. A constellation, viewed from a particular latitude on Earth, that never sets below the horizon is termed circumpolar.
From the North Pole or South Pole, all constellations south or north of the celestial equator are circumpolar. Depending on the definition, equatorial constellations may include those that lie between declinations 45° north and 45° south, or those that pass through the declination range of the ecliptic or zodiac ranging between 23½° north, the celestial equator, 23½° south. Although stars in constellations appear near each other in the sky, they lie at a variety of distances away from the Earth. Since stars have their own independent motions, all constellations will change over time. After tens to hundreds of thousands of years, familiar outlines will become unrecognizable. Astronomers can predict the past or future constellation outlines by measuring individual stars' common proper motions or cpm by accurate astrometry and their radial velocities by astronomical spectroscopy; the earliest evidence for the humankind's identification of constellations comes from Mesopotamian inscribed stones and clay writing tablets that date back to 3000 BC.
It seems that the bulk of the Mesopotamian constellations were created within a short interval from around 1300 to 1000 BC. Mesopotamian constellations appeared in many of the classical Greek constellations; the oldest Babylonian star catalogues of stars and constellations date back to the beginning in the Middle Bronze Age, most notably the Three Stars Each texts and the MUL. APIN, an expanded and revised version based on more accurate observation from around 1000 BC. However, the numerous Sumerian names in these catalogues suggest that they built on older, but otherwise unattested, Sumerian traditions of the Early Bronze Age; the classical Zodiac is a revision of Neo-Babylonian constellations from the 6th century BC. The Greeks adopted the Babylonian constellations in the 4th century BC. Twenty Ptolemaic constellations are from the Ancient Near East. Another ten have the same stars but different names. Biblical scholar, E. W. Bullinger interpreted some of the creatures mentioned in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac, with the Lion as Leo, the Bull as Taurus, the Man representing Aquarius and the Eagle standing in for Scorpio.
The biblical Book of Job also
Wide Field and Planetary Camera 2
The Wide Field and Planetary Camera 2 is a camera installed on the Hubble Space Telescope. The camera was built by the Jet Propulsion Laboratory and is the size of a baby grand piano, it was installed by servicing mission 1 in 1993, replacing the telescope's original Wide Field and Planetary Camera. WFPC2 was used to image the Hubble Deep Field in 1995, the Hourglass Nebula and Egg Nebula in 1996, the Hubble Deep Field South in 1998. During STS-125, WFPC2 was removed and replaced with the Wide Field Camera 3 as part of the mission's first spacewalk on May 14, 2009. After returning to Earth, the camera was displayed at the National Air and Space Museum and the Jet Propulsion Laboratory before returning to its final home at the Smithsonian's National Air and Space Museum. WFPC2 was built by NASA's Jet Propulsion Laboratory, which built the predecessor WF/PC camera launched with Hubble in 1990. WFPC2 contains internal corrective optics to fix the spherical aberration in the Hubble telescope's primary mirror.
The charge-coupled devices in the WFPC2 detected electromagnetic radiation in a range from 120 nm to 1000 nm. This included the 380 nm to 780 nm of the visible spectrum, all of the near ultraviolet and most of the near infrared band; the sensitivity distribution of these CCDs is normal, with a peak around 700 nm and concomitantly poor sensitivity at the extremes of the CCDs' operating range. WFPC2 featured each 800x800 pixels. Three of these, arranged in an L-formation, comprise Hubble's Wide Field Camera. Adjacent to them is a fourth CCD with different optics; this afforded a more detailed view over a smaller region of the visual field. WFC and PC images are combined, producing the WFPC2's characteristic stairstep image; when distributed as non-scientific JPEG files the PC portion of the image is shown with the same resolution as the WFC portions, but astronomers receive a raw scientific image package which presents the PC image in its native, higher detail. To allow scientists to view specific parts of the electromagnetic spectrum the WFPC2 featured a rotating wheel which moves different optical filters into the lightpath.
The 48 filter elements included: A set of standard wideband photometric filters. A graduated filter, featuring a wide range of narrowband filters. By positioning the target object at a precise part of the field, the operator can use an picked narrowband filter. A number of narrowband optical filters tuned to the wavelengths of various atomic emission lines; as predicted, over the course of its mission the WFPC2 experienced degradation of the CCDs, resulting in defective pixels. The telescope's operators perform monthly calibration tests to catalog these. To avoid false positives caused by cosmic rays tripping a given pixel, the output of different calibration shots are compared. Pixels which are "hot" are recorded, astronomers who analyse raw WFPC2 images receive a list of these pixels. Astronomers adjust their photo-processing software to ignore these bad pixels. WFPC2 was superseded for broad-band imaging by the Advanced Camera for Surveys, installed during servicing mission 3B in 2002. However, the early 2007 failure of ACS resulted in WFPC2 returning to its role as Hubble's primary visible light camera.
WFPC2 was removed from HST during Servicing Mission 4 in May 2009, for return to Earth and eventual museum display. It was replaced by Wide Field Camera 3, which features two UV/visible detecting CCDs, each 2048x4096 pixels, a separate IR CCD of 1024 x 1024, capable of receiving infrared radiation up to 1700 nm. Wide Field and Planetary Camera Wide Field Camera 3 Cosmic Origins Spectrograph Advanced Camera for Surveys Near Infrared Camera and Multi-Object Spectrometer Faint Object Camera WFPC2 homepage and user's guide Space Telescope science institute's documentation on the WFPC2 NASA article explaining how color is built from multiple filtered images Wide Field Camera 3 – NASA the WFPC2 at ESA/Hubble Images with the WFPC2 at ESA/Hubble
A quasar is an luminous active galactic nucleus. It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of the Sun. In quasars and other types of AGN, the black hole is surrounded by a gaseous accretion disk; as gas falls toward the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way; the term "quasar" originated as a contraction of quasi-stellar radio source, because quasars were first identified during the 1950s as sources of radio-wave emission of unknown physical origin, when identified in photographic images at visible wavelengths they resembled faint star-like points of light. High-resolution images of quasars from the Hubble Space Telescope, have demonstrated that quasars occur in the centers of galaxies, that some host-galaxies are interacting or merging galaxies.
As with other categories of AGN, the observed properties of a quasar depend on many factors including the mass of the black hole, the rate of gas accretion, the orientation of the accretion disk relative to the observer, the presence or absence of a jet, the degree of obscuration by gas and dust within the host galaxy. Quasars are found over a broad range of distances, quasar discovery surveys have demonstrated that quasar activity was more common in the distant past; the peak epoch of quasar activity was 10 billion years ago. As of 2017, the most distant known quasar is ULAS J1342+0928 at redshift z = 7.54. The supermassive black hole in this quasar, estimated at 800 million solar masses, is the most distant black hole identified to date; the term "quasar" was first used in a paper by Chinese-born U. S. astrophysicist Hong-Yee Chiu in May 1964, in Physics Today, to describe certain astronomically-puzzling objects: So far, the clumsily long name'quasi-stellar radio sources' is used to describe these objects.
Because the nature of these objects is unknown, it is hard to prepare a short, appropriate nomenclature for them so that their essential properties are obvious from their name. For convenience, the abbreviated form'quasar' will be used throughout this paper. Between 1917 and 1922, it became clear from work by Heber Curtis, Ernst Öpik and others, that some objects seen by astronomers were in fact distant galaxies like our own, but when radio astronomy commenced in the 1950s, astronomers detected, among the galaxies, a small number of anomalous objects with properties that defied explanation. The objects emitted large amounts of radiation of many frequencies, but no source could be located optically, or in some cases only a faint and point-like object somewhat like a distant star; the spectral lines of these objects, which identify the chemical elements of which the object is composed, were extremely strange and defied explanation. Some of them changed their luminosity rapidly in the optical range and more in the X-ray range, suggesting an upper limit on their size no larger than our own Solar System.
This implies an high power density. Considerable discussion took place over, they were described as "quasi-stellar radio sources", or "quasi-stellar objects", a name which reflected their unknown nature, this became shortened to "quasar". The first quasars were discovered as radio sources in all-sky radio surveys, they were first noted as radio sources with no corresponding visible object. Using small telescopes and the Lovell Telescope as an interferometer, they were shown to have a small angular size. Hundreds of these objects were recorded by 1960 and published in the Third Cambridge Catalogue as astronomers scanned the skies for their optical counterparts. In 1963, a definite identification of the radio source 3C 48 with an optical object was published by Allan Sandage and Thomas A. Matthews. Astronomers had detected what appeared to be a faint blue star at the location of the radio source and obtained its spectrum, which contained many unknown broad emission lines; the anomalous spectrum defied interpretation.
British-Australian astronomer John Bolton made many early observations of quasars, including a breakthrough in 1962. Another radio source, 3C 273, was predicted to undergo five occultations by the Moon. Measurements taken by Cyril Hazard and John Bolton during one of the occultations using the Parkes Radio Telescope allowed Maarten Schmidt to find a visible counterpart to the radio source and obtain an optical spectrum using the 200-inch Hale Telescope on Mount Palomar; this spectrum revealed the same strange emission lines. Schmidt was able to demonstrate that these were to be the ordinary spectral lines of hydrogen redshifted by 15.8 percent - an extreme redshift never seen in astronomy before. If this was due to the physical motion of the "star" 3C 273 was receding at an enormous velocity, around 47,000 km/s, far beyond the speed of any known star and defying any obvious explanation. Nor would an extreme velocity help to explain 3C 273's huge radio emissions. Although it raised many questions, Schmidt's discovery revolutionized quasar observation.
The strange spectrum of 3C 48 was identified by Schmidt and Oke as hydrogen and magnesium redshifted by 37%. Shortly afterwards, two more quasar spectra in 1964 and five more in 1965, were confirmed as ordinary
National Radio Astronomy Observatory
The National Radio Astronomy Observatory is a Federally Funded Research and Development Center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc for the purpose of radio astronomy. NRAO designs and operates its own high sensitivity radio telescopes for use by scientists around the world; the NRAO headquarters is located on the campus of the University of Virginia in Charlottesville, Virginia. The North American ALMA Science Center and the NRAO Technology Center and Central Development Laboratory are located in Charlottesville, Virginia. NRAO was, until October 2016, the operator of the world's largest steerable radio telescope, the Robert C. Byrd Green Bank Telescope, which stands near Green Bank, West Virginia; the observatory contains several other telescopes, among them the 140-foot telescope that utilizes an equatorial mount uncommon for radio telescopes, three 85-foot telescopes forming the Green Bank Interferometer, a 40-foot telescope used by school groups and organizations for small scale research, a fixed radio'horn' built to observe the radio source Cassiopeia A, as well as a reproduction of the original antenna built by Karl Jansky while he worked for Bell Labs to detect the interference, discovered to be unknown natural radio waves emitted by the universe.
Green Bank is in the United States National Radio Quiet Zone, coordinated by NRAO for protection of the Green Bank site as well as the Sugar Grove, West Virginia monitoring site operated by the NSA. The zone consists of a 13,000-square-mile piece of land where fixed transmitters must coordinate their emissions before a license is granted; the land was set aside by the Federal Communications Commission in 1958. No fixed radio transmitters are allowed within the area closest to the telescope. All other fixed radio transmitters including TV and radio towers inside the zone are required to transmit such that interference at the antennas is minimized by methods including limited power and using directional antennas. With the advent of wireless technology and microprocessors in everything from cameras to cars, it is difficult to keep the sites free of radio interference. To aid in limiting outside interference, the area surrounding the Green Bank observatory was at one time planted with pines characterized by needles of a certain length to block electromagnetic interference at the wavelengths used by the observatory.
At one point, the observatory faced the problem of North American flying squirrels tagged with US Fish & Wildlife Service telemetry transmitters. Electric fences, electric blankets, faulty automobile electronics, other radio wave emitters have caused great trouble for the astronomers in Green Bank. All vehicles on the premises are powered by diesel motors to minimize interference by ignition systems; the NRAO's facility in Socorro is the Pete V. Domenici Array Operations Center. Located on the New Mexico Tech university campus, the AOC serves as the headquarters for the Very Large Array, the setting for the 1997 movie Contact, is the control center for the Very Long Baseline Array; the ten VLBA telescopes are located in Hawaii, the U. S. Virgin Islands, eight other sites across the continental United States. Offices are located on the University of Arizona campus. NRAO operated the 12 Meter Telescope on Kitt Peak. NRAO suspended operations at this telescope and funding was rerouted to the Atacama Large Millimeter Array instead.
The Arizona Radio Observatory now operates the 12 Meter Telescope. The Atacama Large Millimeter Array site in Chile is at ~5000 m altitude near Cerro Chajnantor in northern Chile; this is about 40 km east of the historic village of San Pedro de Atacama, 130 km southeast of the mining town of Calama, about 275 km east-northeast of the coastal port of Antofagasta. The Karl G. Jansky Lectureship is a prestigious Lecture awarded by the Board of Trustees of the NRAO; the Lectureship is awarded "to recognize outstanding contributions to the advancement of radio astronomy." Recipients have included Fred Hoyle, Charles Townes, Edward M. Purcell, Subrahmanyan Chandrasekhar, Philip Morrison, Vera Rubin, Jocelyn Bell Burnell, Frank J. Low and Mark Reid; the lecture is delivered in Socorro. Official website
Very Long Baseline Array
The Very Long Baseline Array is a system of ten radio telescopes which are operated remotely from their Array Operations Center located in Socorro, New Mexico, as a part of the Long Baseline Observatory. These ten radio antennas work together as an array that forms the longest system in the world that uses long baseline interferometry; the longest baseline available in this interferometer is about 8,611 kilometres. The construction of the VLBA began in February 1986 and it was completed in May 1993; the first astrometrical observation using all ten antennas was carried out on May 29, 1993. The total cost of building the VLBA was about $85 million; the array is funded by the National Science Foundation, costs about $10 million a year to operate. Each receiver in the VLBA consists of a parabolic dish antenna 25 meters in diameter, along with its adjacent control building; this contains the supporting electronics and machinery for the receiver, including low-noise electronics, digital computers, data storage units, the antenna-pointing machinery.
Each of the antennas is about as tall as a ten-story building when the antenna is pointed straight up, each antenna weighs about 218 metric tons. The signals from each antenna are recorded on a bank of one-terabyte hard disc drives, the information is time-stamped using atomic clocks. Once the disc drives are loaded with information, they are carried to the Pete V. Domenici Science Operations Center at the NRAO in Socorro. There the information undergoes signal processing in a powerful set of digital computers that carry out the interferometry; these computers make corrections for the rotation of the Earth, the slight shifts in the crust of the Earth over time, other small measurement errors. The Very Long Baseline Array makes radio observations at wavelengths from three millimeters to 90 centimeters, or in other words, at frequencies from 0.3 gigahertz to 96 gigahertz. Within this frequency range, the VLBA observes in eight different frequency bands that are useful for radio astronomy; the VLBA makes observations in two narrow radio bands below one gigahertz that include spectral lines produced by bright maser emissions.
The VLBA radio telescopes are located at: The use of the VLBA can be scheduled dynamically, its sensitivity can be improved by a factor of five by including other radio telescopes such as the Arecibo radio telescope in Puerto Rico, the Green Bank Telescope in West Virginia, the Very Large Array in New Mexico and the Effelsberg radio telescope in Germany. These four additional sites are brought online for as much as 100 hours per four-month trimester. In this configuration, the entire array is known as the High-Sensitivity Array; these sites, with coordinates, are as follows: Distance between each VLBA baseline: The longest baseline in the array is 8,611 kilometres. Minimum angular resolution: List of radio telescopes Official site