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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

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A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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