The Life Cycles of Stars (Grades 9-12) - Page 18
Event Horizon (also known as Schwarzschild Radius) - the virtual surface around a black hole (often considered as the surface of the black hole) within which gravitational forces prevent anything, including light, from escaping
Expansion Velocity - the outward material velocity away from the central point of an explosion, such as a supernova
General Relativity - the geometric theory of gravitation developed by Albert Einstein, incorporating and extending the theory of special relativity to accelerated frames of reference and introducing the principle that gravitational and inertial forces are equivalent
Gravitational Energy - energy that can be released by the gravitational collapse of a system
Hertzsprung-Russell Diagram - a plot of absolute magnitude versus spectral type (or temperature) for a group of stars
Isotope - any of two or more forms of the same element, whose atoms all have the same number of protons but different numbers of neutrons
Kinetic Energy - energy associated with motion; the kinetic energy of an object is equal to one-half the product of its mass and the square of its velocity
Light-Year - the distance light travels in one Earth year, equal to 9.46 x 1012 km
Luminosity - the rate of radiation of electromagnetic energy into space by a star or other object
Main-Sequence - diagonal region of the Hertzsprung-Russell diagram in which most stars are located; generally these are stable stars during the bulk of their lives
Neutron - a subatomic particle with no electrical charge; one of the constituents of the atomic nucleus
Neutron Star - a star of extremely high density composed almost entirely of neutrons
Nuclear Reaction - a reaction, as in fission, fusion, or radioactive decay, that alters the energy, composition, or structure of an atomic nucleus
Parsec - unit of distance often used by astronomers, equal to 3.2616 light-years (a kiloparsec is equal to 1,000 parsecs)
Photon - a unit of electromagnetic energy associated with a specific wavelength or frequency
Planetary Nebula - a shell of gas ejected from, and expanding away from, a star that is nearing the end of its life
