1. What is the diameter of our galaxy, the Milky Way?
1. Diameter of our galaxy is about 100,000 light-years.
2. How far from the center of the galaxy is the solar system? What else besides stars are in the galaxy?
3. Label the following where appropriate: spiral arms, disk, halo, bulge, globular clusters, galactic center
3. see text book for better pictures .
1. Traveling through empty space, starlight arrives at Earth unchanged. What happens to the spectrum we observe if there is a gas cloud (no dust) between us and the star?
2. What happens to the spectrum we observe if there is a dusty interstellar cloud between us and the star?
2. Dust in a gas cloud selectively scatters blue light out of our line of sight. Therefore the spectrum of the star would appear to us to have less blue light than its spectral type says it has. Therefore, from our perspective, the light from the star has been "reddened." This is called interstellar reddening.
1. If the universe were contracting instead of expanding, how would we know (what would the observations be)?
If the universe were contracting, the radial velocities of all the distant galaxies would be blue-shifted. Instead, we see that they are all red-shifted.
2. In a spiral galaxy, stars in the disk all orbit the galactic center within the disk. In an elliptical galaxy, stars orbit the galactic center like bees in a hive—at all angles.
(look at other side for question. Answer---->) 4. Since the Andromeda galaxy is significantly larger than the Milky Way, there will most likely be extreme tidal distortion of our galaxy. It is not likely, however, that any stars will collide since the space between stars is so great.
4 The Andromeda galaxy and the Milky Way are rushing toward each other at a velocity of 130 km/s (or, 300,000 mph!). We will collide in about 60 billion years. Andromeda is about one and a half times larger in diameter and in mass than our Milky Way. Describe what might happen during and after the collision.
5. The Hubble Deep Field image shows (in true color) that some galaxies are red and some are blue. Why is this? Do spiral or elliptical types tend to be one color or the other? If so, why might this be the case?
1. No. The galaxies fly around the center of mass of the Local Group like bees around a hive.
2. Will any of the galaxies in the Local Group eventually leave, flying off into intergalactic space?
2. No. The speeds of the galaxies in our group are below what they would need to escape the system.
With a traditional optical telescope, the space between stars and galaxies (thebackground) is completely dark. But a sufficiently sensitive radio telescope shows a faint background glow, almost exactly the same in all directions, that is not associated with any star, galaxy, or other object.