The K-Rations Cosomological Cross-Reference Dictionary
While piecing together Case Studies for the Hotseat, it became apparent that the words
and phrases used in Cosmology (the science and theory of the universe) are often far
removed from our everyday language.
Based on the dictionary created by NASA's Laboratory for High Energy Astrophysics, the
K-Rations Cosmological Cross Reference Dictionary is less esoteric and high-end user, and
instead caters more for the entry to mid level enquirer, and assumes little or no prior
knowledge of matters cosmological.
A -- B -- C -- D -- E -- F -- G --
H -- I -- J -- K
L -- M -- N -- O -- P -- Q -- R -- S -- T
U -- V -- W -- X -- Y -- Z
Words underlined indicate that these are yet to be
cross-referenced.
A class of galaxies which spew massive amounts of energy from their centres,
far more than ordinary galaxies. Many astronomers believe supermassive
black holes may lie at the centre of these galaxies and power their explosive
energy output.
A quantity obtained by multiplying the mass of an orbiting body by its velocity
and the radius of its orbit. According to the conservation laws of physics,
the angular momentum of any orbiting body must remain constant at all points in the orbit,
i.e., it cannot be created or destroyed. If the orbit is elliptical the radius
will vary. Since the mass is constant, the velocity changes. Thus planets
in elliptical orbits travel faster at periastron and more slowly at apastron. A spinning body also possesses spin angular momentum.
The point in an orbit when the two objects are farthest apart. Special names
are given to this orbital point for commonly used systems: see apastron,
aphelion, and apogee.
All Sky Monitor. An instrument designed to observe large areas of the sky for
interesting astronomical phenomena. An ASM measures the intensity of many sources
across the sky and looks for new sources.
The scientific study of matter in outer space, especially the positions,
dimensions, distribution, motion, composition, energy, and evolution of celestial
bodies and phenomena.
Emission or absorption lines in the spectrum of hydrogen that arise from
transitions between the second (or first excited) state and higher energy states of the hydrogenatom. They were discovered by Swiss physicist J. J. Balmer.
BATSE (Burst and Transient Source Experiment) is an instrument aboard the Compton
Gamma Ray Observatory that detects and locates gamma-ray bursts in the sky.
A non-radiating ball of gas resulting from either a white dwarf that has
radiated all its energy or gas which has contracted but contains too little mass
to begin nuclear fusion.
For interactions between black holes and normal matter, the conservation laws of mass-energy,
electric charge, linear momentum, and angular
momentum, hold. This is analogous to the first law of thermodynamics.
2. Second law of black hole dynamics:
With black-hole interactions, or interactions between black holes and normal matter,
the sum of the surface areas of all black holes involved can never decrease. This is
analogous to the second law of thermodynamics, with the surface areas of the black
holes being a measure of the entropy of the system.
An apparent shift toward shorter wavelengths of spectral lines in the radiation
emitted by an object caused by motion between the object and the observer which decreases
the distance between them. SeeDoppler effect.
Named after the the Dutch/American astronomer who first
discovered them, these dark clouds of dust contain enough material to
form several stars the mass of our Sun.
A constant which describes the relationship between temperature and kinetic
energy for molecules in an ideal gas. It is equal to 1.380622 x 10-23
J/K. Seescientific notation.
(a.k.a Tyge Ottesen) Danish astronomer whose accurate
astronomical observations of Mars in the last quarter of the 16th century formed
the basis for Johannes Kepler's laws of planetary motion. Brahe lost his nose in a
dual in 1566 with Manderup Parsberg (a fellow student and nobleman) at Rostock over who
was the better mathematician. He died in 1601, not of a burst bladder as legend suggests,
but from high levels of mercury in his blood (which he may have taken as medication after
falling ill from the infamous meal).
"braking radiation", the main way very fast charged particles lose
energy when travelling through matter. Radiation is emitted when charged
particles are accelerated. In this case, the acceleration is caused by the electromagnetic
fields of the atomic nuclei of the medium.
A process for translating the signals produced by a measuring instrument, such as a telescope,
into something that is scientifically useful. This procedure removes most of the errors
caused by environmental and instrumental instabilities.
Binary star systems with one white dwarf star and
one normal star, in close orbit about each other. Material from the normal star
falls onto the white dwarf, creating a burst of X-rays.
A type of star which exhibits a regular pattern of changing brightness as a
function of time. The period of the pulsation pattern is directly related to the star's
intrinsic brightness. Thus, Cepheid variables are a powerful tool for determining
distances in modern astronomy.
Indian astrophysicist renowned for creating theoretical
models of white dwarf stars, among other achievements. His equations explained the
underlying physics behind the creation of white dwarfs, neutron stars
and other compact objects.
A limit which mandates that no white dwarf can be more massive than about 1.4
solar masses. Any degenerate object more massive must inevitably collapse into a neutron
star.
The amount of area a telescope has that is capable of collecting electromagnetic
radiation. Collecting area is important for a telescope's sensitivity: the more
radiation it can collect (that is, the larger its collecting area), the more likely
it is to detect dim objects.
An effect that demonstrates that photons have momentum. A photon
fired at a stationary particle, such as an electron, will
impart momentum to the electron and, since its energy
has been decreased, will experience a corresponding decrease in frequency.
The background of radiation mostly in the frequency range 3 x 108 to 3 x 1011
Hz (seescientific notation) discovered in space in 1965. It is believed
to be the cosmologically redshiftedradiation
released by the Big Bang itself.
A constant term which Einstein added to his general theory
of relativity in the mistaken belief that the universe was neither expanding
nor contracting. The cosmological constant was found to be unnecessary once observations
indicated the universe was expanding. Had Einstein
believed what his equations were telling him, he could have claimed the expansion of the Universe
as perhaps the greatest and most convincing prediction of general relativity; he
called this the "greatest blunder of my life".
A distance far beyond the boundaries of our Galaxy. When viewing objects at cosmological distances, the curved nature of spacetime
could become apparent. Possible cosmological effects include time
dilation and redshift.
Name given to the amount of mass whose existence is deduced from the analysis
of galaxy rotation curves but which until now, has escaped all detections. There
are many theories on what dark matter could be. Not one, at the moment is convincing
enough and the question is still a mystery.
Dark nebulae are usually only visible because they hide the light of something in
the background that is bright, such as reflection nebulae or emission nebulae.
Bok globules also fall into this category.
A coordinate which, along with Right Ascension, may be used to locate any
position in the sky. Declination is analogous to latitude for locating
positions on the Earth, and ranges from +90 degrees to -90 degrees.
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. For
example, the optical analogue would be to remove the spikes and halos which often appear
on images of bright stars because of light scattered by the telescope's
internal supports.
The ratio between the mass of an object and its volume. In the metric
system, density is measured in grams per cubic centimetre (or kilograms per litre); the
density of water is 1.0 gm/cm3; iron is 7.9gm/cm3; lead is 11.3.gm/cm3
(a) A flattened, circular region of gas, dust, and/or stars.
It may refer to material surrounding a newly-formed star; material accreting onto a black hole or neutron
star; or the large region of a spiral galaxy containing the spiral arms.
(b) The apparent circular shape of the Sun, a planet, or the moon
when seen in the sky or through a telescope.
The apparent change in wavelength of sound or light caused by the motion of
the source, observer or both. Waves emitted by a moving object as received by an observer
will be blueshifted (compressed) if approaching, redshifted
(elongated) if receding. It occurs both in sound and light. How much the frequency
changes depends on how fast the object is moving toward or away from the receiver. Comparecosmological redshift.
Not the dust one finds around the house (usually fine bits of fabric, dirt, and dead
skin cells). Rather, irregularly shaped grains of carbon and/or silicates measuring a
fraction of a micron across which are found between the stars. Dust is most evident
by its absorption, causing large dark patches in regions of our Milky Way Galaxy
and dark bands across other galaxies, such as in Dark
Nebulae.
A value that defines the shape of an ellipse or planetary orbit. The
eccentricity of an ellipse is the ratio of the distance between the foci and the major
axis. Equivalently the eccentricity is (ra-rp)/(ra+rp) where ra is the apoapsis distance and rp is the periapsis distance.
The passage of one celestial body in front of another, cutting off the light
from the second body (e.g. an eclipse of the sun by the moon, or one star
in a binary system eclipsing the other). It may also be the passage of all or part
of one body through the shadow of another (e.g. a lunar eclipse in which the moon
passes through the Earth's shadow).
The theoretical limit at which the photon pressure would exceed the gravitational
attraction of a light-emitting body. That is, a body emitting radiation at
greater than the Eddington limit would break up from its own photon pressure.
German-American physicist; developed the Special and General Theories of
Relativity which along with Quantum Mechanics is the foundation of modern physics.
The change of potential energy experienced by an electron
moving from a place where the potential has a value of V to a place where it has a value
of (V+1 volt). This is a convenient energy unit when dealing with the motions of electrons and ions in electric fields; the unit is also
the one used to describe the energy of X-rays and gamma rays. A keV (or
kiloelectron volt) is equal to 1000 electron volts. An MeV is equal to one million
electron volts. A GeV is equal to one billion (109) electron volts. A TeV is equal to a
million million (1012) electron volts.
The fundamental kinds of atoms that make up the building blocks of matter,
which are each shown on the periodic table of the elements. The most abundant
elements in the universe are hydrogen and helium.
The distance from a black hole within which nothing can
escape. In addition, nothing can prevent a particle from hitting the singularity
in a very short amount of proper time once it has entered the horizon. In this sense, the
event horizon is a "point of no return". SeeSchwarzschild radius.
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 characterized by loss of mass from its
surface in the form of a stellar wind.
The K-Rations Cosomological Cross-Reference Dictionary