# Cosmic Times 1993 Glossary

afterglow

Light emitted after removing the source of energy.

Andromeda Galaxy

A large spiral galaxy visible to the naked eye. The spiral galaxy is 2.2
million light-years from Earth in the constellation Andromeda in the
Northern Hemisphere between Lacerta and Perseus and south of Cassiopeia

astrophysicist

A person who studies the part of astronomy that deals principally with
the physics of the universe, including luminosity, density, temperature,
and the chemical composition of stars, galaxies, and the interstellar
medium.

baryon

Any of the subatomic particles that interact via the strong nuclear
force. Most commonly, these are protons and neutrons. Their presence in
the universe is determined through their gravitational and
electromagnetic interactions.

binary stars

Binary stars are two stars that orbit around a common center of mass. An
X-ray binary is a special case where one of the stars is a collapsed
object such as a white dwarf, neutron star, or black hole, and the
separation between the stars is small enough so that matter is
transferred from the normal star to the compact star, producing X-rays
in the process.

blackbody radiation

Blackbody radiation is produced by an object that is a perfect absorber
of heat. Perfect absorbers must also be perfect radiators. For a
blackbody at a temperature T, the intensity of radiation emitted I at a
particular energy E is given by Plank\'s law:

I(E,T) = 2 E^3^\[h^2^c^2^(e^E/kT^ - 1)\]^-1^

where h is Planck\'s constant, k is Boltzmann\'s constant, and c is the
the speed of light.

blackbody temperature

The temperature of an object if it is re-radiating all the thermal
energy that has been added to it; if an object is not a blackbody
radiator, it will not re-radiate all the excess heat and the leftover
will go toward increasing its temperature.

Boltzmann constant

A constant that 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 (see scientific notation).

Cepheid

Type of variable star that 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.

COBE

The Cosmic Background Explorer satellite used to measure the diffuse
infrared and microwave radiation from the early universe to the limits
set by our astrophysical environment.

**contortion**

A twisting or deforming action.

**cosmic microwave background (CMB)**

The background of radiation mostly in the frequency range 3 x 10^8^ to
3 x 10^11^ Hz (see scientific notation) discovered in space in 1965. It
is believed to be the cosmologically red shifted radiation released by
the Big Bang itself.

**cosmology**

The astrophysical study of the history, structure, and dynamics of the
universe.

**dark matter**

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.

**deviation**

The difference between a value in a frequency distribution and the
average

**dissipate**

To spread thin and eventually vanish.

**electro-weak force**

The unification of the electromagnetic force and the weak nuclear force

**galactic disk**

The galactic disc is the plane in which the spirals, bars and discs of
disc galaxies exist. This area tends to have more gas and dust, and
younger stars than galactic bulges, or galactic haloes.

**Grand Unified Theory**

The Grand Unified Theory attempts to combine the four forces that are
known (gravity, electromagnetism, strong nuclear, and weak nuclear) into
one theory.

**gravitational waves**

Ripples in space-time caused by the motion of objects in the universe.
The most notable sources are orbiting neutron stars, merging black
holes, and collapsing stars. Gravitational waves are also thought to
emanate from the Big Bang.

**gravity**

A mutual physical force attracting two bodies.

**intrinsic brightness**

Intrinsic brightness is also called absolute magnitude tells how bright
a star would be without the effects of distance or absorption due to
interstellar dust or gas.

**light year**

A unit of length used in astronomy that equals the distance light
travels in a year. At the rate of 300,000 kilometers per second (671
million miles per hour), 1 light-year is equivalent to 9.46053 x 10^12^
km, 5,880,000,000,000 miles or 63,240 AU.

**luminosity-decline relation**

A correction factor for supernovae that are dimmer than the standard
Type Ia supernova which allows astronomers to measure distance more
accurately.

**MACHOS**

MAssive Compact Halo Objects -- one possible type of Dark Matter.

**microwave**

Electromagnetic radiation that has a longer wavelength (between 1 mm and
30 cm) than visible light. Microwaves can be used to study the Universe,
communicate with satellites in Earth orbit, and cook popcorn.

**minuscule**

Very small

**neutrinos**

A fundamental particle produced in massive numbers by the nuclear
reactions in stars; they are very hard to detect because the vast
majority of them pass completely through the Earth without interacting.

**pulsar**

A rotating neutron star which generates regular pulses of radiation.
Pulsars were discovered by observations at radio wavelengths but have
since been observed at optical, X-ray, and gamma-ray energies.

**quantum fluctuations**

A temporary change in energy at a given point due to variations
predicted by the Heisenberg Uncertainty Principle. These variations
could have caused inflation.

**quarks**

Subatomic particles that make up baryons and mesons. Three quarks are
needed to make a proton or a neutron.

**ROSAT**

The ROentgen SATellite that was an X-ray satellite launched in 1990

**strong nuclear force**

One of the four fundamental forces. The strong nuclear force or
interaction is the strongest of the fundamental forces. It holds the
nucleus together. It is the interaction of quarks and gluons in the
nucleus.

**supernova (plural: supernovae)**

(a)The death explosion of a massive star, resulting in a sharp increase
in brightness followed by a gradual fading. At peak light output, these
type of supernova explosions (called Type II supernovae) can outshine a
galaxy. The outer layers of the exploding star are blasted out in a
radioactive cloud. This expanding cloud, visible long after the initial
explosion fades from view, forms a supernova remnant (SNR).

\(b\) The explosion of a white dwarf that has accumulated enough
material from a companion star to achieve a mass equal to the
Chandrasekhar limit. These types of supernovae (called Type Ia) have
approximately the same intrinsic brightness, and can be used to
determine distances.

**Type 1a supernovae**

See b above, in supernova definition. Supernovae of predictable
intrinsic brightness that can be used as a "standard candle".

**Type 2 supernovae**

Supernova that do not have the telltale lines of hydrogen in the
spectrum.

**white dwarf**

A star that has exhausted most or all of its nuclear fuel and has
collapsed to a very small size. Typically, a white dwarf has a radius
equal to about 0.01 times that of the Sun, but it has a mass roughly
equal to the Sun\'s. This gives a white dwarf a density about 1 million
times that of water!

**Wien\'s displacement law**

For a blackbody, the product of the wavelength corresponding to the
maximum radiance and the thermodynamic temperature is a constant. As a
result, as the temperature rises, the maximum of the radiant energy
shifts toward the shorter wavelength (higher frequency and energy) end
of the spectrum.

**WIMPs**

Weakly Interacting Massive Particles that might be a candidate for dark
matter in the universe. They interact through the weak nuclear force and
gravity.

**X-ray**

Electromagnetic radiation of very short wavelength and very high-energy;
X-rays have shorter wavelengths than ultraviolet light but longer
wavelengths than gamma rays.