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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