Chapter 4
Vocabulary
Stars, Galaxies, and the
Universe
the moment in time when the
universe started to expand out of
an extremely hot, dense state
big bang
the process in which particles of an
element collide and combine to form
a heavier element
fusion
a cloud of gas and dust in space,
where stars can form
nebula
the apparent shift in position of an
object when viewed from different
locations
parallax
the transfer of energy from place to
place by the motion of heated liquid
or gas
convection
a change in the observed
frequency of a wave, occurring
when the source of the wave or the
observer is moving
Doppler effect
the stage in the life cycle of stars
during which stars produce energy
by fusing hydrogen and helium
main sequence
the distance light travels I one year,
which is about 9.5 trillion kilometers
of 6 trillion miles
light-year
the outer layer of the Sun’s
atmosphere
corona
the very bright center of a distant
galaxy
quasar
a dense core that may be left behind
after a higher-mass star explodes into a
supernova
neutron star
a stream of electrically charged
particles that flows out in all
directions from the Sun’s corona
solar wind
a darker, cooler spot on the
photosphere
sun spot
the final stage of an extremely massive
star, which is invisible because its
gravity prevents any form of radiation
from escaping
black hole