Astro101V: Final Exam

Name:

This is a take-home exam, and is due on or before Tuesday, March 16, 1999 at 5:00 pm. This deadline is firm, and I will not accept exams handed in after 5:00 pm on Tuesday, March 16.

You may hand in the exam to me personally in my office (PAB B370), slide it under the door, put it in my mailbox in the astronomy office (PAB C321), or via e-mail to my e-mail address: palen@astro.washington.edu.

You may use your class notes, or information out of your own head, or the textbook, but using information out of other people's heads is bad form and WILL NOT BE TOLERATED. Remember that if I can't decipher what you've written, I can't give you any credit! Also, remember that a picture or diagram is often worth athousand words, and a thousand hours of thought...

If you have a question about the meaning of one of the questions, feel free to e-mail me: palen@astro.washington.edu , or to call me in my office: (206) 543-2604. I may not be able to answer your question, but it's worth a shot.

### Cumulative Portion:

1. (5 points) Suppose that the moon rises tonight at 6:00 pm. Tomorrow, will it rise earlier or later? (Remember, a good picture will help!)

2. (5 points) Here's a question from Marilyn's column in Parade magazine:
When we go on daylight savings time, we get an extra hour of sunlight each day. Do you think that extra sunlight will help the corn grow, or cause it to dry up?

What's wrong with this question?

3. (10 points) The popular movie, Deep Impact, begins with a scene in which an astronomer is looking through his telescope. Suddenly, he discovers a comet. Using his calculator, he determines that "It's headed right for us!" Using what you know about how we determine the motions of objects in the sky, argue that this scene is completely bogus.

4. (10 points) Draw an H-R diagram. Why is this such a useful tool for astronomers?

5. (10 points) During the formation of the solar system, two laws of physics were acting which caused the shape that exists today. What were they?

6. (10 points) Define the following in one or two sentences:
1. a giant molecular cloud
2. a star
3. a planet
4. a galaxy
5. a galaxy cluster
6. a binary star system
7. an elliptical galaxy
8. a telescope
9. the Universe
10. a neutrino

7. (15 points) Describe the life cycle of a star.

8. (15 points) Stars evolve because their chemical composition changes. List and give a brief description (a few sentences) of each of the three ways in which a changing chemical composition affects a star.

9. (20 points) You are Dr. Iowa Johnson, the not-quite-famous-yet archeo-astronomer. It is the dead of winter, and your mentor, Dr. Indiana Jones, has just informed you of an interesting new archeological site in Turkey, which may contain the dessicated corpse of a genuine Atlantean! You are quite happy to go someplace sunny and warm, so you hop on the plane, and head to Turkey, where Dr. Jones is waiting to lead you to the site.

Along the way, he tells you that they have determined that the site is ~13,000 years old, using carbon dating techniques. They believe that the site is of religious significance, since there are stones aligned to bracket the Sun at the equinoxes, and a pair of tall stones aligned so that you can sight along them and locate the North Star. You check this out for yourself, and using your compass, find that the equinox stones are indeed aligned perpendicularly to your compass needle. Examining the rocks, you find a diagram inscribed on one of them that shows a familiar pattern of dots. On a hunch, you take a piece of paper, and trace the pattern, making holes at each of the dots.

Night falls, and you continue your investigations. You sight along the pair of tall stones, and can see Polaris, winking at you from just over the top of the second stone. You turn to the South, and hold up your paper to the sky, aligning three of the holes with the belt of Orion. Each of the other holes is filled with a star. You can see Sirius, Aldebaran, Rigel and Betelgeuse, as well aas several other stars. Triumphant, you exclaim, "This site is a fake! It cannot possibly be 13,000 years old!" You explain your reasoning to Dr. Jones, using two astronomical facts and one geological fact. Dr. Jones is so impressed that he gives you the honorary Ph.A.D. (Phamous Archeologist Degree), which has been your life-long dream. What were the two astronomical facts, and how did they contradict the evidence at the site? For 5 points extra credit, what was the geological fact, and how did it contradict the evidence at the site?

### Non-Cumulative Portion

1. (10 points) Argue that spiral galaxies may evolve into ellipticals. Why do we now think that this is not true?

2. (10 points) What would happen if the Sun were suddenly replaced by a one solar mass black hole?

3. (10 points) Why is a galaxy more likely to collide with another galaxy than a star is to collide with another star?

4. (10 points) In what sense is an elliptical galaxy "all halo"?

5. (10 points) What is the evidence for dark matter in galaxies?

6. (10 points) How do we know that the Universe is expanding?

7. (10 points) Under what conditions would the expansion age of the Universe be the actual length of time that has passed since the Big Bang?

8. (10 points) The Cosmic Microwave Background Radiation was emitted by gas that was about 3000 K (about half the temperature of the Sun). Why does it now represent a 2.74 K blackbody?

9. (20 points) You are walking down the street in Pike Place Market one pleasant, sunny day. Up ahead there is a weird-looking little guy harrassing people. He gets right up in people's faces, and berates them. They look startled, move off the sidewalk a bit, and keep moving. You are just hanging out, so you walk up to the guy to find out what's going on. He leans in close to you, and hisses "I am Nrfdrt, from the planet Bliknast. Tell me where I am or I will destroy your world." You notice that he has two pairs of eyelids, like a cat. The inner lid slides across his eyeball, and weirds you out. Thinking fast, you decide that one of two things is true. Either he's really an alien, in which case, somebody better answer the question, or he's just a nut, in which case, if somebody answers his question, it might help him out. You have time. Why not answer the question? You begin to tell him, "Well, you are in the City of Seattle, on the North American continent, on the planet Earth, orbiting a star called the Sun..." He blinks weirdly at you again, and seems to be growing more agitated. "Tell me where I am," he insists. You think a minute, then you smile. You swiftly draw him two rough sketches of the galaxy, one from the top, and one from the side, indicating the location of the Sun on each picture. Then you take him to the University library of all places, and get him a photocopy of the catalog that contains the information that he needs to precisely pinpoint his location. He looks at the catalog and points to two columns of numbers. He looks at you. "What are these?" he asks. "Right ascension and declination", you reply. You draw him yet a third picture as an explanation. He nods, smiles, and hands you a very large platinum brick. "Thanks!" he says, and disappears. You are now rich beyond your wildest dreams. The only problem will be in convincing people that you aren't completely mad.

a, b) Draw the two sketches that would enable the alien to have an idea of his location in the Galaxy. Be sure to indicate the position of the Sun!

c) What is the information contained in the catalog that you showed to the alien? Explain why this would tell him what he needs to know.

d) What is the third picture that you drew? Reproduce it here. Hint: you've drawn this one before, way back at the beginning of class!