Chapter 14 Our Galaxy

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Chapter 14Our Galaxy
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14.1 The Milky Way Revealed

• Our Goals for Learning
• What does our galaxy look like?
• How do stars orbit in our galaxy?

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What does our galaxy look like?
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The Milky Way galaxy appears in our sky as a
faint band of light
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Dusty gas clouds obscure our view because they
absorb visible light This is the interstellar
medium that makes new star systems
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All-Sky View
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We see our galaxy edge-on Primary features
disk, bulge, halo, globular clusters
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If we could see the Milky Way from above the
disk, wed see its spiral arms and other
components, including a central bar
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The Milky Way Galaxy also has a bar of stars and
gas in its center
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How do stars orbit in our galaxy?
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Stars in the disk all orbit in the same direction
with a little up-and-down motion
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Orbits of stars in the bulge and halo have random
orientations
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Why do orbits of disk stars bob up and down above
and below the disk?

• Disk stars are attached to the interstellar
  medium
• Other disk stars gravity pulls them back
• Halo stars knock them back into the disk

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Suns orbital motion (radius and velocity) tells
us mass within Suns orbit 1.0 x 1011 MSun

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What have we learned?

• What does our galaxy look like?
• The Milky Way Galaxy consists of a thin disk
  about 100,000 light-years in diameter with a
  central bulge and a spherical region called the
  halo that surrounds the entire disk. The disk
  contains the gas and dust of the interstellar
  medium, while the halo contains very little gas.

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What have we learned?

• How do stars orbit in our galaxy?
• Stars in the disk all orbit the galactic center
  in about the same plane and in the same
  direction. Halo and bulge stars also orbit the
  center of the galaxy, but their orbits are
  randomly inclined to the disk of the galaxy.

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Activity 46, part I, page 171

• Well answer all parts of questions 1-3.

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Clicker Question. BUT FIRST

• Check your clicker ID. Is it one of these?
• 00872E
• 01B4AA
• If so, YOU ARE NOT GETTING CREDIT FOR YOUR
  ANSWERS. Please register your clicker correctly.

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1B How far away (in kpc) is the Sun from the
center of the galaxy?

• About 0 kpc
• About 2.5 kpc
• About 7.5 kpc
• About 10 kpc
• About 12.5 kpc
• About 20 kpc
• About 30 kpc

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1C Does your X fall on the x-axis, meaning that
the constellation of Sagittarius lies in the
plane of the Milky Way?

• Yes
• No

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2. The Milky Way consists of the _, which
contains spiral arms, the _, which contains
globular clusters, and the _, which contains the
Galaxys center and a bar of stars, gas dust.

• Bulge, disk, halo
• Bulge, halo, disk
• Disk, halo, bulge
• Disk, bulge, halo
• Halo, disk, bulge
• Halo, bulge, disk

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46, 3 In the edge-on sketch of the Milky Way on
the board, what are the labels?

• A bulge B disk C halo
• A bulge B halo C disk
• A disk B halo C bulge
• A disk B bulge C halo
• A halo B bulge C disk
• A halo B disk C bulge

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46, 3 How far is the Sun from the center of our
Galaxy?

• About 3 light-years
• About 30 light-years
• About 300 light-years
• About 3,000 light-years
• About 30,000 light-years
• About 300,000 light-years
• About 3,000,000 light-years