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Life Cycles of Stars (Grades 9-12) - Page 17


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´┐Żs kinetic energy is equal to its gravitational potential energy)

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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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