The Very Long Baseline Array (VLBA) is a system of ten

radio telescope 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 ...

s which are operated remotely from their

Array Operations Center The Array Operations Center (AOC) in Socorro, New Mexico, is the control and monitor center for the Very Long Baseline Array. From the AOC, National Radio Astronomy Observatory operators are able to remotely control and monitor the ten VLBA teles ...

located in Socorro, New Mexico, as a part of the National Radio Astronomy Observatory (NRAO). These ten

radio antenna In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an ...

s work together as an array that forms the longest system in the world that uses

very long baseline interferometry 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. T ...

. The longest baseline available in this

interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

is about . 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 The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...

, and costs about $10 million a year to operate. Each receiver in the VLBA consists of a

parabolic dish antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or p ...

meter The metre (British spelling) or meter (American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pref ...

s (82 feet) in diameter, along with its adjacent control building. This contains the supporting

electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

and machinery for the receiver, including low-noise electronics,

digital computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These pro ...

s, data storage units, and the antenna-pointing machinery. Each of the antennas is about as tall as a ten-story building when the antenna is pointed straight up, and each antenna weighs about 218

metric ton The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton (United States c ...

s (240

short ton The short ton (symbol tn) is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The vari ...

s). The signals from each antenna are recorded on a bank of approximately one-

terabyte The byte is a units of information, unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character (computing), character of text in a computer and for this ...

hard disc drives, and the information is time-stamped using

atomic clock An atomic clock is a clock that measures time by monitoring the resonant frequency of atoms. It is based on atoms having different energy levels. Electron states in an atom are associated with different energy levels, and in transitions betwee ...

s. 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 Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as audio signal processing, sound, image processing, images, and scientific measurements. Signal processing techniq ...

in a powerful set of digital computers that carry out the interferometry. These computers also make corrections for the rotation of the Earth, the slight shifts in the

crust of the Earth Earth's crust is Earth's thin outer shell of rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the crust and the upper part of the mantle. The ...

over time, and other small

measurement error Observational error (or measurement error) is the difference between a measured value of a quantity and its true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. In statistics, an error is not necessarily a "mistake ...

Observations by the VLBA

The Very Long Baseline Array usually makes radio

observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The ...

s at

wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase on the wave, such as two adjacent crests, tro ...

s from three

millimeter 330px, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is between 1 meter to 1 millimeter. The millimetre (American and British English spelling differences#-re, -er, ...

s to 90

centimeter 330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter. A centimetre (international spelling) or centimeter (American spellin ...

s, or in other words, at

frequencies Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...

from 0.3

gigahertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one h ...

to 96 gigahertz. Within this frequency range, the VLBA observes in eight different

frequency band A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum. The frequency range of a system is the range over which i ...

s that are useful for radio astronomy. The VLBA also 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:

High-Sensitivity Array

The use of the VLBA can be scheduled dynamically, and its sensitivity can be improved by a factor of five by including other radio telescopes such as the

Green Bank Telescope The Robert C. Byrd Green Bank Telescope (GBT) in Green Bank, West Virginia, US is the world's largest fully steerable radio telescope, surpassing the Effelsberg 100-m Radio Telescope in Germany. The Green Bank site was part of the National Radio ...

in West Virginia, the

Very Large Array 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, ~ west of Socorro. The VLA comprises twen ...

(VLA) in New Mexico and the

Effelsberg radio telescope The Effelsberg 100-m Radio Telescope is a radio telescope in the Ahr Hills (part of the Eifel) in Bad Münstereifel, Germany. For 29 years the Effelsberg Radio Telescope was the largest fully steerable radio telescope on Earth, surpassing the ...

in Germany. These three 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 (HSA). The

Arecibo radio telescope The Arecibo Telescope was a spherical reflector radio telescope built into a natural sinkhole at the Arecibo Observatory located near Arecibo, Puerto Rico. A cable-mount steerable receiver and several radar transmitters for emitting signals we ...

in Puerto Rico was also used, before it collapsed.

Baseline distance and angular resolution

Distance between each VLBA baseline (km): The longest baseline in the array is .

References

External links

* {{Authority control Radio telescopes Interferometric telescopes Kitt Peak National Observatory 1993 establishments in the United States

Observations by the VLBA

High-Sensitivity Array

Baseline distance and angular resolution

See also

References

External links