18.10 NOTES
What are galaxies?
Objective: Describe the three main types of galaxies
A galaxy is a huge selection of stars, gas, and dust that travel together through
space. Using the newest telescopes, astronomers can see billions of galaxies.
Galaxies have different shapes. There are three kinds of galaxies: elliptical,
irregular, and spiral.
Elliptical galaxies are shaped like a ball or
slightly flattened ball. The stars in these
galaxies are usually older than stars in
other galaxies. They are larger than
irregular galaxies, but smaller than spiral
galaxies.
Galaxies with NO SHAPE are called irregular.
They are the smallest and faintest galaxies,
but also the most common kind of galaxy.
Spiral galaxies are shaped like
flattened disks. They usually have one
or more spiral arms that branch out
from their centers. One type of spiral
galaxy is called the barred spiral. The
arms branch out from the end of a
short bar made up of stars and gas.
The Milky Way is our home galaxy.
The Milky Way is part of a group of
more than 20 other galaxies.
Together, these galaxies are known
as the Local Group.
The Milky Way is a spiral galaxy,
containing about 100,000 billion
stars. The distance from edge to
edge of the spiral arms is about
100,000 light years. The Sun is two-thirds of the way from the center of the Milky
Way.
The Milky Way was given its name because its band of stars looks like a river of
milk.
Neighboring galaxies include Andromeda (2 million light years away), and the
Large Magellanic Cloud, and the small Magellanic Cloud. These irregular galaxies
are 160,000 and 200,000 light years away.