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Glossary

AIPS++ (Astronomical Image Processing System in C++)

A computer software package for processing astronomical images now under developement. AIPS is a similar package that is already widely used in astronomy (mostly radio astronomy). AIPS++ represents the next generation in astronomical image processing by employing object-oriented programming techniques with the C++ programming language. (See also NewSW.)

Amino acid

the chemical building blocks that make up proteins that are important to life on Earth. (See also astrochem.)

Antenna

an instrument for receiving radio waves. The BIMA telescope is made up of several antennas linked together. Because of their shape, antennas like those that make up the BIMA telescope are sometimes referred to as "dishes". (See also text in mainarray HighPlanDish, GtrSensitiv, and DataIncr.)

Astrochemistry

the study of the chemical interactions between the gases and dust interspersed between the stars. (See also text in astrochem.)

Atomic gas

gas that is composed of individual atoms (such as hydrogen or carbon) that are not bound to each other as molecules. Atomic gas may be ionized or mixed with molecular gas. (See also text in tracers.)

Baseline

a pair of radio dish antennae seperated by some distance but connected together as part of a radio interferometer telescope. (See also text in baselines.)

Berkeley-Illinois-Maryland-Association (BIMA)

an organization of astronomers from the University of California at Berkeley, the University of Illinois at Urbana-Champaign, and the University of Maryland at College Park cooperating together to expand and maintain the millimeter interferometer at the Hat Creek Observatory. (See also the Bima Home Page.)

Black Hole

the massive, compact object that remains after a massive star exhausts its fuel and explodes as a supernova. Gravity is so strong on the surface of a black hole that not even light can escape it. (See also StarDeath.)

Blanca Testbed

an experimental, high-speed (600 Megabits per second) computer network link between the NCSA at the University of Illinois at Urbana-Champaign and the University of Wisconsin at Madison. The Blanca Testbed is used to develope new methods for high-speed communication between computers seperated by great distances. (See also text in testbed.)

Calibration

a process for translating the signals produced by a measuring instrument (such as a telescope) into something that is scientifically useful. For instance, the electrical signals produced by the BIMA telescope must be calibrated in order to turn them into an image of the radio light coming from an object in space. This procedure removes most of the errors caused by atmospheric and instrumental instabilities. (See also text in ImgForm and calibration.)

Collecting Area

the amount of area of telescope that is capable of collecting light. For instance, each BIMA antenna with its 6-meter diameter dish has a collecting area of about 113 square meters. Collecting area is important for a telescope's sensitivity: the more light it can collect (that is, the larger its collecting area), the more sensitive it is to dim objects. (See also text in GtrSensitiv.)

Comet

Chunks of rock and ice that orbit the Sun. Most comets reside in a sphere surrounding our solar system almost a light year away from the sun called the Oort cloud, though some get gravitationally "bumped" into closer orbits, bringing them close enough for us to see them as fuzzy objects with an extended tail. (See also the text in comets.)

Configuration

for an interferometer telescope, a arrangement of the antennas. For instance, the BIMA Array has three standard arrangements for its six movable antennas: a compact configuration (with the antennas close together), an intermediate configuration, and an extended configuration (with the antennas spread far apart from each other). The compact configuration gives the lowest resolution, and the extended configuration gives the highest. (See also text in Baselines.)

Correlation

a mathematical combination of the electrical signals from two radio antennae resulting in the basic measurement of a radio interferometer (called a visibility ). Many correlations from many pairs of antennae are combined to produce a radio image of the sky. (See also text in computation, and baselines.)

Declination

a coordinate which, along with right ascension, may be used to locate any position in the sky. Declinatin is analogous to latitude for locating positions on the Earth. (See also text in ChanMp, and Ave.)

Deconvolution

an image processing technique that removes features in an image that are caused by the telescope itself rather than from actual light coming from the sky. (See also text in deconv.)

Digital library

A library in which the "books" are files stored on a computer and are accessable over the computer networks. These files might be electronic versions of actual books or documents, but they can also be astronical images and other data. An example of a digital library is the library.)

Dish

in radio astronomy, another word for antenna.

Doppler Effect

an effect in which the frequency of light or sound coming moving object is different when it is received compared to when it was emitted. How much the frequency changes depends on how fast the object is moving toward or away from the receiver. (See also the text in doppler and Spec.)

Electromagnetic Spectrum

The full range of frequencies, from radio waves to gamma waves, that characterizes light. (See also the text in spectrum.)

Electromagnetic Waves (radiation)

Another term for light. Light waves are fluctuations of electric and magnetic fields in space. (See also the text in spectrum, and doppler.)

Evolved Star

A star near the end of its lifetime when most of its fuel has been used up. This period of the star's life is characterised by loss of mass from its surface in the form of a stellar wind. (See also text in StarDeath.)

Fast Fourier Transformation (FFT)

A Fourier Transform is the mathematical operation that takes measurements made with a radio interferometer and transforms them into an image of the radio sky. The Fast Fourier Transform is technique used by computer programs that allows the Fourier Transform to be computed very quickly. (See also text in ImgForm and FFT.)

Frequency

a property of a wave that describes how many of wave patterns or cycles pass by in a period of time. Frequency is often measured in Hertz (Hz), where a wave with a frequency of 1 Hz will pass by at 1 cycle per second. (See also text in spectrum.)

Galaxy

a component of our universe made up of gas and a large number (usually more than a million) of stars held together by gravity. (See also text in ExtraGal and GalCntr.)

Giant Molecular Cloud (GMC)

Massive clouds of gas in interstellar space composed primarily of hydrogen molecules (two hydrogen atoms bound together), though also containing other molecules observable by radio telescopes. These clouds can contain enough mass to make several million stars like our Sun and are often the sites of star formation. (See also text in GMC and StarForm.)

Grand Challenges

Research initiatives identified by the U.S. National Science Foundation to tackle fundamental problems in science and engineering that will make broad scientific and/or economic impact. The Grand Challenge in radioastronomy is to develop the computational resources for rapid data processing and image formation necessary to achieve realtime astronomy. (See also text in maincomp and realtime.)

High Speed Network

communication lines between computers that can transfer large amounts of data very quickly. (See also text in testbed and CompPwr.)

Image

in astronomy, a picture of the sky. (See also text in maincomp and computation.)

Interferometer

a type of telescope in which signals from two or more small telescopes are combined to produce an image with the resolution of a much larger telescope. The larger the seperation between the individual telescopes, the higher the resolution of the resulting image. (See also text in baselines.)

Interstellar Medium

The gas and dust that exists in the space between the stars. (See also text in GMC and StarDeath.)

Ionic (or Ionized) Gas

Gas whose atoms have losed or gained electrons, causing them to be electrically charged. In astronomy, this term is most often used to describe the gas around hot stars where the high temperature causes atoms to lose electrons. (See also text in tracers.)

Kelvin

a temperature scale often used in sciences such as astronomy. The Kelvin temperature scale is just like the Celsius scale except that the freezing point of water, zero degrees Celsius, is equal to 273 degrees Kelvin. [ K = C + 273 degrees => F = 9/5C + 32 degrees ] (See also text in GMC.)

Kinematics

Refers to the calculation or description of the underlying mechanics of motion of an astronomical object. For example, in radioastronomy, spectral line graphs are used to determine the kinematics or relative motions of material at the center of a galaxy or surrounding a star as it is born.

Large Scale Structure

The largest spatial features in an image. (See also text in SpacRes, SpecObsTech, LrgSclStruct, and LosLrg.)

Light Year

a unit of length used in astronomy equal to the distance that light can travel in a year (about 10 trillion kilometers or 6 trillion miles). (See also text in ExtraGal.)

Megabits per Second

a unit for measuring how fast data can be sent through a computer network equal to one million bits per second. (See also text in testbed.)

Metacomputer

a collection of computers connected by a network that work together to solve a specific problem. For example, real time imaging with the BIMA telescope might involve the computer driving the telescope, a supercomputer for creating the images from the raw data, and the astronomer's workstation for displaying the results; these computers could be spread across the country but communicating with each other over the network. (See also text in testbed.)

Meter
a unit of length equal to about 39 inches.

Molecular Gas

gas that is composed of atoms that are bound to each other as molecules. The most abundant molecule is space is molecular hydrogen (two hydrogen atoms bound to each other) followed by carbon monoxide (CO, or a carbon and oxygen atom bound together). Molecular gas may be mixed with atomic gas. (See also text in tracers, StarForm, StarDeath, and astrochem.)

Mosaicing

a technique for combining observations of overlapping regions of the sky to produce a single large image. Mosaicing BIMA data together is particularly important for revealing the large-scale structure of gas clouds in space. (See also text in SpecObsTech.)

Noise

the random fluctuations that is always associated with a measurement that is repeated many times over. Noise appears in astronomical images as fluctuations in the image background. These fluctuations do not represent any real sources of light in the sky, but rather are caused by the imperfections of the telescope. If the noise is too high, it may obscure the dimmest objects within the field of view. (See also text in deconv and SelfCal.)

Oort Comet Cloud

a spherical cloud believed to surround our Solar System about a light year away from the sun. This cloud contains debris left over from the formation of the Solar System. It is thought to be the source of comets which occasionally get gravitationally "bumped" into orbits that bring them within view of the Earth. (See also text in comets.)

Opacity

a property of matter that prevents light from passing through it; non-transparent. The opacity or opaqueness of something depends on the frequency of the light. For instance, the atmosphere of Venus is transparent to ultra-violet light, but is opaque to visual light.

Pointing

the direction in the sky to which the telescope is pointed. Pointing also describes how accurately a telescope can be pointed toward a particular direction in the sky. For example, the pointing of the BIMA antennas can be affected by strong winds which cause the antennas to move about slightly. (See also text in SpecObsTech.)

Protostar

very dense regions (or cores) of molecular clouds where stars are in the process of forming. (See also text in StarForm.)

Radial Velocity

the speed at which an object is moving away or toward an observer. By observing spectral lines, astronomers can determine how fast objects are moving away from or toward us; however, these spectral lines cannot be used to measure how fast the objects are moving across the sky. (See also text in Spec and Mov.)

Radio Map

an image of the sky made from radio waves. (See also text in maincomp and computation.)

Radiotelescope

a telescope that observes radio waves from space and turns them into images. (See also text in BimaHome, mainarray, and differs.)

Radio Waves

a form of light with a frequency that is much lower than visual light. (See also text in differs.)

Realtime Observational Astronomy

the fast processing of signals from a telescope to turn them into an images at the same time that the observations are being made. Traditionally, it could take astronomers several hours or days to create radio images from interferometer data. Supercomputers and fast networks have the potential to remove this delay, so that astronomers can look at the images as the data is recorded. (See also text in maincomp, realtime, CompPwr, and testbed.)

Resolution (Spatial)

in astronomy, the ability of a telescope to differentiate between two objects in the sky which are seperated by a small angular distance. The closer to two objects can be while still allowing the telescope to see them as two distinct objects, the higher the resolution of the telescope. (See also text in differs, resolution HighPlanDish, and SpacRes.)

Resolution (Spectral or Frequency)

Similar to spatial resolution except that it applies to frequency, spectral resolution is the ability of the telescope to differentiate two light signals which differ in frequency by a small amount. The closer the two signals are in frequency while still allowing the telescope to seperate them as two distinct components, the higher the spectral resolution of the telescope. (See also text in HighSpec and FreqRes.)

Right Ascension

a coordinate which, along with declination, may be used to locate any position in the sky. Right ascension is analogous to longitude for locating positions on the Earth. (See also text in ChanMp and Ave.)

Observing Run

the period of time when observations are made with the telescope for a particular scientific project. With the BIMA telescope, an observing run is typically about 8 hours of observing time; an astronomer may conduct three observing runs for a particular project, one in each of the array's configurations. (See also text in mainarray, HighSpec, HighPlanDish, and computation.)

Self-Calibration

a data processing technique for improving the calibration of data from an interferometer by removing errors cause by disturbances in the Earth's atmosphere. It is called self-calibration because it uses observations of the unknown source, rather than the calibrator source, to improve the image of the unknown source. (See also text in ImgForm and SelfCal

Sensitivity

a measure of how bright objects need to be in order for that telescope to detect these objects. A highly sensitive telescope can detect dim objects, while a telescope with low sensitivity can detect only bright ones. (See also text in HighPlanDish and GtrSensitiv.)

Small Scale Structure

The smallest spatial features in an image. (See also text in SpacRes and LrgSclStruct.)

Solar Flares

violent eruptions of gas on the sun's surface. (See also text in flares.)

Spectral Line

light given off at a specific frequency by an atom or molecule. Every different type of atom or molecule gives off light at its own unique set of frequencies; thus, astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of its characteristic frequencies. For example, carbon monoxide (CO) has a spectral line at 115 GigaHertz (or a wavelength of 2.7 mm). (See also text in spectrum, CBCSpecLines, doppler, tracers, HighSpec, Spec, ChanMp, and astrochem.)

Spectrometer

the instrument connected to a telescope that seperates the light signals into different frequecies, producing a spectrum. (See also text in HighSpec, FreqRes, ExtraGal, astrochem, and StarDeath.)

Spectroscopy

the study of spectral lines from different atoms and molecules. Spectroscopy is an important part of studying the chemistry that goes on in interstellar clouds. (See also text in HighSpec.)

Spectrum

a plot of the intensity of light at different frequencies. (See examples of spectra in Spectral Line Graphs.)

Stellar wind

the ejection of gas off the surface of a star. Many different types of stars, including our Sun, have stellar winds; however, a star's wind is strongest near the end of its life when it has consumed most of its fuel. (See also text in StarForm and StarDeath.)

Sunspots

cooler (and thus darker) regions on the sun where the magnetic field loops up out of the solar surface. (See also text in flares.)

Supercomputer

a computer that uses state-of-the-art technology to achieve high-speed computations. (See also text in CompPwr, testbed, and NewSW.)

Tracer

a particular atom or molecule which, when observed in a interstellar cloud, can be used to determine the physical properties of the cloud, such as its density or temperature. (See also text in tracers, and astrochem.)

21-cm Line

The spectral line given off by atomic hydrogen with a wavelength of 21 cm (or frequency of 1.4 GigaHertz). Since hydrogen is the most abundant atom in the universe, the 21-cm line of hydrogen is an extremely useful tool for radio astronomers. (See also text in astrochem.)

Waveband

portions of the electromagnetic spectrum. Examples of differnt wavebands include the infrared, visual, radio wavebands. (See also text in ComRes and spectrum.)

Wavelength

a property of a wave that gives the length between two peaks of the wave. (See also text in spectrum.)

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NCSA. Last modified 11/21/95