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Types of Galaxies
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Mr. Pfeffenberger
Elliptical Galaxies
Most common type of galaxy
–  Shape – small/large, 3-dimensional ellipse
or round
–  Smooth,featureless appearance and appear
basically the same from any angle.
–  Made up of old stars and containing a small
amount of gas, and dust.
–  Most are yellow and red because they do not
contain young stars.
–  Vary in size from small to extremely large
Elliptical Facts
•  - do not have a disc or arms
•  - smooth, baseball or football shaped
•  - the smallest elliptical is called a
“dwarf” elliptical and appears to be the
most common type of galaxy
•  - the stars do not revolve around the
center in an organized way. Their
movement is randomly oriented
Elliptical Galaxy
Spiral Galaxies
Spiral arms winding outward from inner
regions
–  Loose, lumpy spiral arms (two or more) are made
of bright blue young stars in the cstar and yellow
stars throughout the disc, and dust. Most arms
start close to the center of the galaxy; so it has a
small central bulge. It is referred to as a pinwheel
shape.
–  Made mainly of young stars and contains a large
amount of gas.
Spiral galaxies II
–  Example - Andromeda
so far away that you can’t see its individual stars. It appears
as a hazy spot in our sky.
–  It is about 2.2 million light years away
Spiral Galaxy with 3 main components: bulge, disk and halo
Barred Spiral Galaxy
•  A pinwheel-shaped galaxy containing
many new stars and a large amount of
gas.
•  A “bar” of stars, dust and gas runs
across its center
Light year
•  The distance that light travels in one
year.
•  Light travels at 300,000 km/s, or about
9.5 trillion kilometers in one year.
•  The nearest star to earth other than the
sun is Proxima Centauri.
•  It is 4.2 light years away, or about 40
trillion kilometers.
Irregular Galaxies
–  No definite structure
–  Smaller and less common than other
galaxies
–  Tend to have a blue or white color
because recent star formation
makes galaxies appear blue.
–  Composed of both young and old
stars, and it contains large amounts
of gas and dust.
Irregular Galaxy
Milky Way
–  Contains more than 400 billion
stars and may contain up to 1
trillion
–  The visible disc of stars Is about
100,000 light years across
–  The sun is located about 30,000
light years out from its center
Milky Way
•  The Sun orbits the center of the Milky
Way once every 240 million years
–  Scientists do not know if it is a barred spiral
galaxy or a normal spiral galaxy
Spiral Galaxy - Our Milky Way