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Chapter 18 - The Universe

Terms in this set (18)

universe
The totality of all matter, energy and space.
parsec
The distance to a star when the star exhibits a parallax of one second of arc.
photosphere
The bright, visible "surface"of the Sun.
apparent magnitude
The brightness of a star (or other celestial object) as observed from Earth.
absolute magnitude
The brightness of a star would have if it were placed at a standard distance of 10pc from Earth.
H-R diagram
A plot of the absolute magnitude of stars versus the temperature of their photosphere.
main sequence
The narrow band of stars going from the lower tight to the upper left on the H-R diagram; most stars fall into this category.
red giant
A relatively cool, very bright star that has a diameter ten to a hundred times larger than the Sun.
white dwarf
A hot white star that has a much smaller diameter and much higher density an average. It is believed to be the final stage of a low-mass star.
nova
A white dwarf star that suddenly increases dramatically in brightness for a brief period of time.
supernova
An exploding star.
neutron star
An extremely high-density star composed almost entirely of neutrons.
black hole
An object so dense that even light cannot escape from its surface because of the object's intense gravitational field.
nebulae
Cool dense clouds of interstellar gas and dust.
galaxy
An extremely large collection of stars bound together by mutual gravitational attraction.
dark matter
The as-yet-unidentified nonluminous matter in the universe.
dark energy
A mysterious energy that seems to be causing the expansion of the universe to accelerate.
Big Bang
Theory of the beginning of the universe that states that the known universe was smaller, hotter and denser in the past, and that is began rapidly expanding 13.8 billion years ago.
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