These are the most frequently used words in this book.
0
another
apparent
appear
astronomers
atmosphere
between
black
body
bright
celestial
center
cloud
comet
craters
day
diameter
different
direction
disk
distance
earth
effect
energy
even
explain
fact
few
field
figure
first
form
found
galaxy
gas
great
however
hydrogen
jupiter
km
known
large
less
light
lines
magnetic
magnitude
mars
mass
material
matter
mean
might
million
moon
motions
now
object
observer
orbit
part
particles
period
planet
point
pole
position
probe
radiation
radio
regions
result
ring
rotation
satellite
saturn
see
seen
show
sky
small
solar
space
stars
sun
surface
system
telescope
temperature
though
thought
time
two
type
universe
used
venus
visible
wavelengths
years