Chapter 14 Our Galaxy

14.1 The Milky Way Revealed Our Goals for Learning • What does our galaxy look like? • How do stars orbit in our galaxy?

What does our galaxy look like?

The Milky Way galaxy appears in our sky as a faint band of light

Dusty gas clouds obscure our view because they absorb visible light This is the interstellar medium that makes new star systems

All-Sky View

We see our galaxy edge-on Primary features: disk, bulge, halo, globular clusters

If we could see the Milky Way from above the disk, we’d see its spiral arms and other components, including a central bar…

The Milky Way Galaxy also has a bar of stars and gas in its center

How do stars orbit in our galaxy?

Stars in the disk all orbit in the same direction with a little up-and-down motion

Orbits of stars in the bulge and halo have random orientations

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 :00

Sun’s orbital motion (radius and velocity) tells us mass within Sun’s orbit: 1.0 x 1011 MSun

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.

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.

Activity #46, part I, page 171 We’ll answer all parts of questions 1-3.

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.

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 :00

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 :00

2. The Milky Way consists of the _, which contains spiral arms, the _, which contains globular clusters, and the _, which contains the Galaxy’s 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 :00

#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 :00

#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 :00