Glossary
Absolute Magnitude - apparent magnitude a star would have
if placed at a distance of 10 parsecs from Earth
Accretion - gradual accumulation of mass
Accretion Disk - a disk of material falling in toward a massive
object such as a neutron star or black hole (the disk shape is the result
of conservation of angular momentum)
Active Galactic Nuclei - galaxies whose central regions are
emitting enormous amounts of electromagnetic radiation
Apparent Magnitude - a measure of observed light flux received from
an object at the Earth
Arc Minutes - a unit of measurement used for very small angles;
there are 60 arc minutes in one degree
Arc Seconds - a unit of measurement used for very small angles;
there are 60 arc seconds in one arc minute
Black Dwarf - the presumed final state of evolution of a low mass
star in which no radiation is emitted
Black Hole - region in space where the escape velocity is equal to,
or greater than, the speed of light. Thus, nothing (including radiation)
can escape from it
Electrical Repulsion - the force which acts between particles of
like electrical charge to repel them from each other
Electromagnetic Radiation - radiation consisting of periodically
varying electric and magnetic fields that vibrate perpendicular to each
other and travel through space at the speed of light
Electromagnetic Spectrum - the full range of electromagnetic
radiation spread out by wavelength, it consists of gamma-rays, X-rays,
ultraviolet rays, optical light, infrared radiation, microwaves, and radio
waves
Electron - a negatively charged subatomic particle that normally
moves about the nucleus of an atom
Escape Velocity - minimum velocity an object must achieve to break
free from the gravity of another body (in physics, it is achieved when the
objectÆs kinetic energy is equal to its gravitational potential energy)
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