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glossary
The Universe
absolute magnitude — the true brightness of a star based on its
actual luminosity, or light output.
apparent magnitude — the apparent brightness of a star as
observed from Earth.
black dwarf — the burned-out core of a white dwarf star.
black hole — the theoretical remains of a supermassive star that
has exploded and collapsed in on itself. No light can escape from
a black hole because its gravity is so strong.
brown dwarf — a starlike object that does not radiate energy
because it has insufficient mass for nuclear fusion.
constellation — a group of stars that form a pattern or shape in the
night sky.
cosmology — a branch of astronomy concerned with the study of
the origin and evolution of the universe.
dark matter — matter that cannot be detected with current
technology. It is too cold and dark to see or measure; scientists
believe it makes up about 90 percent of the universe.
fusion — a nuclear reaction in the center of a star that releases
a tremendous amount of energy in the form of radiation. In most
stars, two hydrogen atoms are fused into a helium atom.
galaxy — a group of stars, usually numbering in the billions, that
orbit a common mass and travel through the universe as a single
unit. Our galaxy is called the Milky Way.
gravity — the universal force of attraction that pulls all matter
together.
H-R Diagram — a plot of stars that shows their relative brightness
and temperature; first developed by Enjar Hertzsprung and Henry
Norris Russell.
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glossary
The Universe
light-year — the distance a beam of light in a vacuum travels in
one year, about 5.88 trillion miles.
nebula — derived from the Latin word for “cloud,” a fuzzy patch
of light in the night sky. Nebulae appear in many forms and are
thought to be clouds of dust and gas, frequently the remains of
exploded stars.
neutron star — a small, extremely dense star composed mostly
of neutrons, or the remains of a supernova explosion.
nova — a stellar explosion of a red giant star, ending in a planetary
nebula and a white dwarf.
parsec — a distance of 3.26 light-years; used to measure immense
distances in space.
planetary nebula — a ring of dust and gas blown off a red giant
star after it undergoes an explosion.
pulsar — a rapidly spinning neutron star that sends out pulses of
radiation at regular intervals. Pulsars have extremely strong
magnetic fields.
quasar — quasi-stellar radio source. A very energetic distant object
that may be powered by a black hole; possibly a galaxy in the
early stages of formation.
red giant — an unstable star whose hydrogen has run out; it burns
helium at its core. The surface of the star is much cooler, which
produces its red color. A red giant usually becomes a nova and
ultimately a white dwarf.
red shift — the apparent shift in a spectrum of light coming from
a star or distant galaxy to the red end. Red shifts indicate that an
object is moving away.
white dwarf — a remnant of a red giant star that has exploded.
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