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Stars and Galaxies

TermDefinition
Light-year the distance light travels in a year, about 9.5 trillion kilometers
Apparent-magnitude the brightness of a star when viewed from Earth
Absolute-magnitude the apparent brightness of a star if it were viewed from a distance of 32.6 light-years; used to compare the true brightness of stars
Hertzsprung-Russel Diagram a plot of stars according to their magnitudes and temperatures
Main-sequence star a star that falls into the main-sequence category on the H-R diagram, contains the majority of stars, and runs diagonally from the upper left to the lower right on the H-R diagram
Binary star one of two stars revolving around a common center of mass under their mutual gravitational attraction
Cepheid variable a star whose brightness varies periodically because it expands and contracts; a type of pulsating star
Nova a star that explosively increases in brightness
Protostar a collapsing cloud of gas and dust destined to become a str; a developing star not yet hot enough to engage in nuclear fusion
Supernova an exploding star that increases in brightness many thousands of times
Pulsar a variable radio source of small size that emits radio pulses in very regular periods
Black hole a massive star that has collapsed to such a small volume that its gravity prevents the escape of everything, including light.
Galaxy a group of stars, dust, and gases held together by gravity
Hubble's Law a law that states that the galaxies are retreating from the Milky Way at a speed that is proportional to their distance
Big Bang Theory the theory that proposes that the universe originated as a single mass, which subsequently exploded
Created by: user-1986754
 

 



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