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Astronomy
The study of
objects and matter
outside the earth's
atmosphere and
of their physical
and chemical
properties
Light Year
•
A unit of
distance in
astronomy;
distance that light
travels in one year
or about 5.88
trillion miles (9.46
trillion kilometers)
Universe
• The entire
celestial
cosmos
Star
A light-radiating
gaseous celestial
body of great mass
which produces
energy by means
of nuclear fusion
reactions
Galaxy
•
Any of the
very large
groups of stars
and matter that
are found
throughout the
universe
System
• a group of
related
natural
objects or
forces
Milky Way Galaxy
The galaxy of which
the Sun and the
solar system are a
part and which
contains the many
stars that make up
the galaxy
Big Bang Theory
Theory that states
that the universe
originated billions of
years ago in an
explosion from a
single point of
nearly infinite
energy density
Cluster
A collection of
stars or galaxies
that appear close
together in the
sky and are
gravitationally
associated
Telescope
•
An optical
instrument
for viewing
distant
objects.
Eyepiece Lens
• The lens
of a
telescope
that makes
the image
larger
Objective Lens
• The lens of
a telescope
that collects
and focuses
light
Spiral Galaxy
Galaxy that
looks like a flat
disk with a
bulge in its
center and
spiral arms
Constellation
Groups of
stars that
seem to form
patterns in
the sky.
Polaris
The star that
is above
Earth’s north
pole
Spectroscope
An instrument
for forming
and
examining
spectra.
Galaxy
A huge,
gravitationally
bound system of
stars, interstellar
gas and dust
Sun
The star in
our Solar
System,
which all the
planets orbit
Apparent Magnitude
A star’s
brightness
as it appears
from Earth
Absolute Magnitude
A star’s
actual size
and
temperature
Nebula
A cloud of
gas and dust
in outer
space
Astronomical Unit
Used to measure
distances within our
solar system; the
average distance
between the Sun
and the Earth;
about 150 million
kilometers; AU
Period of Revolution

The motion of
the planet in its
orbit around the
Sun; the Earth’s
revolution is 1
year
Period of Rotation
The time it
takes for one
complete spin
of a planet on
its axis; the
Earth’s rotation
is 1 day
Inner Planet
Mercury,
Venus, Earth,
Mars; much
smaller and
less massive
than the outer
planets
Outer Planet
Jupiter, Saturn,
Uranus,
Neptune; more
gaseous, larger
and less dense
Comet
A small body
orbiting the Sun
and occasionally
exhibits an
atmosphere and
a tail
Asteroid
Chunk of rock and
metal and found
between the orbits
of Mars and
Jupiter in the
asteroid belt.
Meteoroid
A chunk of
rock that
orbits the
Sun
Meteorite
A
meteoroid
that has
entered the
Earth’s
atmosphere
.
Red Shift
A movement of the
spectrum of a
celestial body
toward longer
wavelengths that is
a result of the
Doppler effect
Focal Point
The point at
which light
rays meet to
form an
image.
Elliptical Galaxy
More rounded
and are often
longer in one
direction than
in the other,
like a football
Irregular Galaxy
Appear
to have
no
definite
shape.
Spectral Analysis
Studying the
“fingerprints” or
spectral lines
of elements
given off by
stars
Red Giant
A star that has
low surface
temperature
and a diameter
that is large
relative to the
Sun
Super Giant
A star of very
great natural
luminosity and
enormous size
Main Sequence
Contains most of the
stars visible to the
naked eye; stars
where there is a
direct relationship
between brightness
and size, includes
our Sun
White Dwarf
A small whitish star
of low natural
brightness usually
with a mass
approximately
equal to that of the
sun but with a
density many times
larger
Neutron Star
Hypothetical dense
celestial object that
consists mostly of
closely packed
neutrons and that
results from the
collapse of a much
larger stellar body
Black Hole
A hypothetical
celestial object with a
gravitational field so
strong that light
cannot escape from it
which is believed to
be created in the
collapse of a very
massive star
Supernova
The explosion of a
very large star in
which the star may
reach a maximum
luminosity one
billion times that of
the sun
H-R Diagram
A chart that
plots the data
of stars
according to
their surface
temperature
and brightness.
Solar System
The Sun together
with the group of
celestial bodies
that are held by
its gravitational
attraction and
revolve around it
Local Group
The cluster
that contains
our galaxy, the
Milky Way
Planet
Any of the
large bodies
that revolve
around a star
in a star
system
Satellite
A celestial
body
orbiting
another of
larger size
Axis
A straight line
about which a
body or a
geometric
figure spins
Seasons
Division of the
year, based on
yearly periodic
changes in the
weather; results
from the tilt of
Earth’s axis
Hemisphere
Northern or
southern half of the
earth divided by the
equator or the
eastern or western
half divided by a
meridian
Equinox
Occurs during March
and September,
where all parts of
Earth received equal
amounts of sunlight,
and the day and the
night are the same
length