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Stars and Galaxies Chapter 15 Review Questions
Terms in this set (19)
Suppose you tried to determine where we are in the galaxy by looking in different directions to see how many stars you could see. You would conclude that we are:
in the center of the galaxy
Why does a simple survey, as described in the previous slide, give us a false answer?
Interstellar dust blocks our view. We are in the center of what we can see, but we miss a lot of the Milky Way.
Since dust scatters blue light more than red, stars seen through a lot of interstellar dust would look:
redder than expected for their spectral type
Why is it difficult to get a good picture of what our Milky Way galaxy looks like?
1. We're in the middle of one of its arms, so we have poor perspective
2. It is very large and the edges are far away and faint.
3. Dust blocks our view when we look toward the center or in the plane.
4. No one has ever taken a photo from both the top and side of it.
All of the above
How do we get a good picture of what our Milky Way galaxy looks like?
1. Use infrared or microwaves to penetrate the dust.
2. Use radio telescopes to see where clouds of hydrogen gas are.
About how long does light take to reach us from the nearest star to our sun (the sun takes about 8 minutes)?
About four years
About how long does light take to cross the Milky Way galaxy?
About 100,000 years
What does our galaxy look like?
1. A large disk with spiral or pinwheel arms; relatively flat and thin
2. Clouds of gas and dust in the spiral arms
3. Older yellow stars in the central bulge
4. Old stars and globular clusters in a spherical halo above and below the disk.
All of the above
Which of the following is a viable way to estimate the mass of our galaxy?
a. Count all the stars and multiply by the average mass of a star.
b. Make an estimate of the number of stars and multiply the average mass of a star.
c. Observe the speed of rotation using the Doppler shift. Knowing the orbital size and speed calculate the mass using Kepler's law.
b and c
When you calculate the Milky Way's mass using the two methods of the previous slide, what do you find?
The mass you estimate for all the visible stars is only 1/10 the mass you get from observing motions.
How do astronomers interpret the results of the previous slide?
90% of the galaxy is unseen. There seems to be a new kind of matter: dark matter.
Gas is added to the interstellar medium by supernovae and planetary nebulae. What kind of gas would you expect that to be?
Gas that has a mix of heavier elements in it, such as carbon, oxygen, silicon, iron, etc.
Stars we see in the halo of our galaxy (or in globular clusters) formed even before the Milky Way collapsed into a disk. Since we see them now, they must be:
b and c
Why do stars in the halo of the galaxy have little of the common elements such as carbon, nitrogen, and oxygen.
The halo stars formed before these elements were made.
Infrared telescopes penetrate dust and show us that stars at the center of the Milky Way are orbiting very fast. Why?
There probably is a massive black hole at the center of the galaxy, with strong gravity
Based on the idea of chemical enrichment, which types of stars contain a higher proportion of heavy elements: stars in globular clusters or stars in open clusters?
Stars in open clusters because they are younger and therefore formed from more enriched material.
What causes the blue and red colors to come out in a photograph of a typical nebula.
The blue color is due to the scattering of light by interstellar dust grains and the red color arises from a hydrogen emission line
Many spectacular ionization nebulae are seen throughout the Milky Way's halo.
No, there are no young, hot stars that cause ionization nebulae in the halo
The sun's velocity around the Milky Way tells us that most of our galaxy's dark matter lies within the sun's orbit.
No, the Milky Way's rotation curve remains flat well beyond the orbit of the sun, indicating that the majority of the Milky Way's mass lies beyond the sun's orbit.
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