Download Introduction to Galaxies 5/23/2013 BR: Milky Way Scale The Milky

Introduction to Galaxies
5/23/2013
BR: Milky Way Scale
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The Milky Way has a diameter of approximately
8.25 x 109 AU (8.25 billion AU).
206,265 AU = 3.26 ly
What is the diameter of the Milky Way in lightyears?
Modeling the Milky Way
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The orbit of Pluto has a diameter of 80 AU.
What is this diameter in ly?
If we think of the extent of our solar system
being Pluto's orbit, what percentage of the
diameter of the Milky Way is the size of our
solar system?
(Take your answer about Pluto and divide by
your bell ringer answer.)
Milky Way Galaxy spiral
The Milky Way is made up
of approximately 100 billion
stars including our Sun.
The center or nucleus of the
Milky Way galaxy is
in the center of a disk.
The nucleus is surrounded
by a nuclear bulge.
The galaxy is shaped like
a disk with a halo around it.
Galactic Center
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Globular clusters on the outside of the Milky Way,
which are located far from our Solar System, are
centered on a specific point and appear to orbit the
center of the Milky Way.
The center of the Milky Way is a region of very high
star density, most of which is obscured by interstellar
gas and dust.
Motion of stars that orbit close to the galactic center
indicate that this area has about 2.6 million times the
mass of the Sun but is smaller than our solar system.
Something this massive could only be a black hole.
Spiral Arms
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Many galaxies including the Milky Way are shaped like
disks with a central bulge and spiral arms.
It is been more difficult for astronomers to determine
the shape of the Milky Way than other galaxies
because astronomers have no way to get outside of
the galaxy and look down on the disk.
As a result, they have to use measurements of
hydrogen emission to detect the four major spiral arms
and numerous minor arms of the Milky Way.
Galaxy Formation
Other Galaxies
Astronomers have been aware of the
existence of galaxies outside the
Milky Way for centuries, though it
took until Edwin Hubble's discovery
of Cepheid variable stars in 1924
and his measurements of their
distance to determine that they
were too far away to be located in
our galaxy and therefore must be in
another galaxy (in this case the
Andromeda Galaxy).
Galaxy Classification – Spiral Galaxies
Normal spiral galaxies
Barred spiral galaxies
(elongated central region)
Galaxy Classification
Elliptical galaxies
Irregular galaxies