Life Cycles of Stars (Grades 9-12) - Page 17
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 object�s kinetic energy is equal to its gravitational potential energy)
