The Structure of the Milky Way Galaxy

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The Structure of the Milky Way Galaxy

• What is the size, shape, and nature of the system
  of stars in which we live?

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You can learn a lot by looking at the sky and
thinking
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From this picture, lets figure out the shape of
the Milky Way. Characteristics to go on are

• Sprinkling of stars everywhere
• Thick band of light across the sky (the Milky
  Way)
• Band brightest in the direction of Sagittarius
• Band faintest in the direction of Taurus-Auriga

Whats the answer?
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The Answer
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Lets get quantitative about the thickness and
diameter of the galactic disk. We start with the
thickness of the galactic plane.
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(No Transcript)
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Measure the distance over which the density of
stars significantly falls off with height above,
or distance below, the galactic plane. The
distance depends on the type of objects
considered, but is roughly 100 200 parsecs.
The galactic plane is much thinner than it is
wide.
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How far is it to the galactic center?

• How could we know?

Hint provided by globular star clusters. Great
summertime objects, few in winter
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How globulars indicate the distance to the
galactic center
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Globular Clusters are Distant

• It must be a long way to the galactic center