### Astro 3 and 4 - Extra Credit Essay Questions

Write a page or two on the essay question which I assign to you. Please do it on a computer and then print it. It's very hard to read most handwritten versions, but if your writing is legible I will take handwritten versions.

1. Imagine the earth were twice as large as it is now. Made of the same material and the same density, but just twice the diameter. How many times more would you weigh? Use Newton's law of gravity to figure it out.

2. First, answer this: roughly how many lunar eclipses happen per year and how many solar eclipses happen on Earth per year (think about "eclipse seasons") - how do those two numbers compare? Google, for help. Next, consider that if you stay put here in Santa Cruz, you'll see total eclipses of the moon several times per decade. However, you can expect to see a total eclipse of the sun maybe once in a 1000 years. Explain the reasons why these two are so different.

3. The moon appears to many people to be larger when it first rises on the horizon than when it is overhead. Is the angular size of the moon larger, or smaller, or the same... when it's high over head vs when it's right on the horizon? What are the reasons for your answer? Hint: there are two main reasons.

4. It's always nice to do diagrams to the proper scale. But in astronomy, that's a big problem. So, here's a simple math exercise which anyone in my Astro classes should be able to do. If I draw the earth's orbit on the white board as a circle with a radius of 1 foot, where would I place Alpha Centauri (the closest star besides the sun)? Use the appendix in the text to get the size of the earth's orbit and the distance to Alpha Centauri, and the sizes of units like an A.U., a light year... whatever you might need. Describe where I'd place Alpha Centauri on this scale. Example, the white board is about 20 feet long, my office is about 200 yards away, Soquel's Ugly Mug Coffee Shop is about 1 mile away, Santa Cruz is about 7 miles away, San Francisco about 70 miles away, the Oregon Border about 500 miles away, Alaska about 2000 miles away... and then you can keep going if you need to! Don't guess - show your work if you want credit!

5. The animal figures shown in the Nazca desert of Peru show up clearly only when seen from above. As a result, some UFO enthusiasts argue that the patterns must have been created by aliens. What do you think of this argument? Defend logically your opinion.

6. There is considerable evidence that the destruction of the Great Library of Alexandria early in the first millenium - about half a million books, and the largest repository of western scientific knowledge and research in ancient times - was motivated by religious reasons. Do a google search and present evidence for this conclusion and any interesting details you uncover.

7. Explain clearly the difference between a scientific theory, and a scientific hypothesis. How does a scientific hypothesis differ most fundamentally from a supernatural explanation for a set of phenomena?

8. Do a google search and find out what is the basis for astrological predictions. What is the mechanism which astrologers (some? most? any?) believe is the way in which the planets positions and your birth date/time make you who you are? I'm not asking what a "Sagittarius" person is supposed to be like, I want to find out WHY a "Sagittarius" person is supposed to be this way. Tell me how extensive was your search and what you were able to come up with.

9. Explain the difference between a "solar day" and a "sidereal day". Not just the number of hours and minutes in each; explain the meaning of each. Also, how many sidereal days in a year? How many solar days in a year?

10. In air or water that is colder than your body temperature, thermal energy transfers from you to the cold air or water. Explain why falling into a 32 deg Fahrenheit lake is much more unpleasant than entering naked into a freezer room at 32 deg F. Explain what is going on at a microscopic level which makes for the difference.

11. Spontaneous human combustion: Suppose that, through a horrific act of an angry God, all the mass in your body were suddenly converted into pure energy. In fact, maybe this will be the fate of your Professor Rick - a notorious non-Christian -, who has 68kg of mass. How much energy will be produced by this process when God annihilates Dr. Rick, in Calories? Show your calculation. Compare this to the energy released from a 1 megaton hydrogen bomb (use the text or Google).

12. How much tidal variation in lake water level should you expect to see during the day at Lake Tahoe? Compare to what you expect to see down at Seacliff Beach below campus. Use the ultimate cause of tides to help you explain why the tidal variations in these two cases are different.

13. Three common examples of objects with emission line spectra are storefront neon lights, flourescent light bulbs, and the sodium lights used in many city streets at night. When you look at objects of different colors under such lights, do you see their normal colors (normal; meaning as under sunlight)? Why or why not? What would be the color you'd see from a red emission line object light falling on a pure blue shirt? If you have a red light at home, try it and find out (better do it in a dark room).

14. The Cassini spacecraft has been studying Saturn and doing some great science. Do a google search and list at least 4 important, amazing, and very cool discoveries that have been made. Say at least a couple of sentences or more about each discovery.

15. This one is fun! You're going to simulate the formation of the solar system. Fill a large bowl or bucket with water and sprinkle ground pepper (not whole pepper!) on top. Then, put in a spoon and move it around randomly in a lot of very different directions (i.e. don't just stir it round and round)... randomly, this way, that way, foreward, then reverse, then a right angle... Then, pull the spoon out and watch how it settles down. What happens? How does this relate to the early history of the solar nebula?

16. A 2007 study was relayed in the press as claiming that "obesity is contagious". The popular press actually presented it this way!. Explain why this is a scientifically ignorant statement about the study. Look up the study and then present a more reasonable cause and effect explaining the data.

17. Suppose you wanted to test whether taking multi vitamins/minerals would help elderly people in their mental functions. Tell me how you would design a good test so as to best deal with issues such as the placebo effect, finding cause/effect, etc.

18. Come up with a reason which is NOT already in the text which could explain why we see no alien visitations on Earth, even though a calculation suggests alien visitation was a reasonable thing to expect we would already have seen sometime in the near or distant past. Be specific in making your case; show the logic in why your idea is reasonable. By this I mean, try and anticipate someone (like me!) who might try and poke holes in your explanation, and support your idea against those arguments. Playing both sides of the debate is always a good way to prepare before writing a controversial essay.

19. What is the total mass estimated to be in the Kuiper Belt? Tell in detail how this estimate was made. Don't just give a number. Give the procedure. Read the relevant paper(s) which produce this estimate, and also give the error estimate. Then, do the same for the Oort Cloud.

20. The moon is thought to have been formed by a collisions with a Mars-sized planet soon after Earth formed. Use the Conservation of Angular Momentum to calculate how fast the Earth must have been spinning soon after the collision while the moon was still just above the Earth's surface and most of the debris had settled back onto the Earth. To be definite, find how fast the Earth was spinning when the moon was just 4 Earth radii from the center of the Earth. You'll need to look up the formula for the angular momentum of a spinning solid to get the angular momentum associated with the Earth, and you'll need the formula for the angular momentum contained in an orbiting object as well.