These are the most frequently used words in this book.
above
abundance
antenna
atoms
background
beginning
between
centimeters
chapter
conditions
constant
cosmic
cosmological
degrees
density
deuterium
distance
early
earth
electrons
energy
enough
equal
equilibrium
even
expansion
far
few
first
force
galaxies
given
gravitational
great
helium
however
hubble
hydrogen
interactions
know
known
large
lepton
less
light
lines
mass
matter
microwave
million
minutes
model
must
neutrinos
neutrons
noise
now
nuclear
nuclei
number
observation
order
part
particles
per
percent
photons
positrons
possible
present
produced
proportional
protons
radiation
radio
really
red
second
see
seems
shift
small
speed
stars
state
temperature
theory
thermal
three
thus
time
two
typical
universe
value
velocity
volts
wave
wavelength
years