20 terms

Ch. 25 Vocabulary

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constellation
an apparent group of stars originally named for mythical characters; The sky is presently divided into 88 constellations.
binary star
one of two stars revolving around a common center of mass under their mutual gravitational attraction.
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 distance of 32.6 light-years; used to compare the true brightness of stars.
main-sequence star
a star that falls onto the main-sequence category on the H-R diagram; This category contains the majority of stars and runs diagonally from the upper left to the lower right on the H-R diagram.
red giant
a large, cool star of high luminosity; a star occupying the upper-right portion of H-R diagram.
supergiant
a very large, very bright red giant star.
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 star; a developing star not yet hot enough to engage in nuclear fusion.
supernova
an exploding star that increases in brightness many thousands of times.
white dwarf
a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size, believed to be near its final stage of evolution.
neutron star
a star of extremely high density composed entirely of neutrons.
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.
galaxy cluster
a system of galaxies containing from several to thousands of member galaxies.
Hubble's law
a law that states that the galaxies are retreating from the Milky Way at the speed that is proportional to their distance.
Big Bang theory
a theory that proposes that the universe originated as a single mass, which subsequently exploded.
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