Astronomy 150 Homework

ASTR 150 Homework #1, due next Thursday (Sept 11th): Summarise #1-#7 in a table, but show all work, including any sketches you need.

  1. Compute the altitude of the sun as it crosses the meridian at noon for the following dates: (a) March 21, (b) June 21, (c) Sept 21, and (d) Dec 21. Assume that you live in Moscow, Russia, latitude 56 degrees north.
  2. Repeat #1 for Cairo, Egypt, latitude 30 degrees north.
  3. Repeat #1 if the observer was located at the north pole.
  4. Repeat #1 for a location on the arctic circle, 66.5 degrees north latitude.
  5. Repeat #1 for a location on the Tropic of Cancer, 23.5 degrees north latitude.
  6. Repeat #1 for a location on the Tropic of Capricorn, 23.5 degrees south latitude.
  7. Repeat #1 for a location on the equator.

  8. For Pullman, describe the changing position of the rising and setting sun throughout the year.
  9. You go outside just after dark and face south. The moon is up and off to your right, near the horizon. (a) Is it rising or setting? (b) What is its approximate phase? (c) The next night you go out again at exactly the same time. Where is the moon (higher? lower? not up?)? (d) Did it move east or west? (e) How has the phase changed?

Answers:

For 1-7, use the fact that the altitude of the north celestial pole is the same as your latitude on earth. The equator is 90 degrees from the pole, so the remainder of the half-circle would be the altitude of the celestial equator (at the meridian) or the noontime sun at an equinox. Solstice altitudes vary plus or minus 23.5 degrees from there.

Sun Altitudes in degrees
LatitudeMarch & SeptJune 21Dec 21
56 34 57.5 10.5
30 60 83.5 36.5
90 0 23.5 -23.5
66.5 23.5 47 0
23.5 66.5 90 43
-23.5 66.5 43 90
0 90 66.5 66.5
Note that the maximum altitude is 90 degrees, so that at the equator the noon sun has drifted 23.5 north of straight up, so its altitude is 66.5, but above the north compass point, not the south as in all the other examples (except the tropic of Capricorn at -23.5 latitude and all other southern hemisphere possibilities).

8. The sun rises due east and sets due west on the equinox. In summer the sun rises north of east and sets north of west. In winter the sun rises south of east and sets south of west.

9. (a) The moon is near the western horizon - it must be setting. (b) In angle, the moon is not far from the sun, but it is east of the sun. It's phase must be waxing crescent. (c) The moon travels east 12 degrees per day, so it will be 12 degrees further along the ecliptic the next night. This will be higher in the sky. (d) It moves east (counterclockwise as seen from the north). (e) The phase will have advanced slightly - you will see about 1/15 more of the disk.

ASTR 150 Challenge (Homework) #2, Due Thursday Sept 18:
Answer, experimentally, the following: Is Aristotle right? Does an object twice as heavy fall twice as fast?

Turn in a report, neatly written, on Thursday. Include the following points. * Describe your experimental setup. * Collect data from different trials and record them. * Come to a conclusion and summarize it succinctly.

HW#2 Answer: Aristotle was not right. Although it is hard (outside of a vacuum chamber) to get total simultaneity due to the complications of aerodynamics/air resistance, objects dropped together will reach the ground at the same time, no matter what their mass. I am very interested to see what the students' experimental results will be!

Aristotle was also wrong about his earth-centered cosmology, his chemistry of earth, air, fire, water, and quintessence, and some of his other ideas about physics, such as gravity and magnetism. However, we still revere his rational approach to understanding, where a conclusion must be reached logically, rather than, for instance, on hearsay or from reading it in a book. He also provided us with the basis for the physics of motion that we understand today; the concepts of velocity and that motion can only be induced by application of a force.

ASTR 150 Challenge #3 .pdf

ASTR 150 Homework #4, Due Thursday Oct 2: Zeilik Chapter 4 Study Questions 1,2,3,4,5 and 9,10,11,12,13,14 (questions are the same in both editions).

ASTR 150 Homework #5, due Tuesday, Oct 28. Zeilik Chapter 5 study questions 1, 2, 3, 5, 6, 9, 11, 12, 13 and Problem #1 or #2 depending on edition; the one that calculates the wavelengths of three different frequencies of radio light.

ASTR 150 Homework #6, Due Thursday Nov 6.

Homework 7


Due Nov 20


As always, turn in sheets that are readable (preferably typed) and characterized by complete sentences and correct grammar and punctuation.

  1. Suppose the amount of water vapor in the atmosphere suddenly increased by a large amount. What would happen to the earth's surface temperature? Answer: an increase in a "greenhouse" heat-trapping gas like water vapor (or CO2 or methane) will have the effect of increasing the average ground-level temperature.
  2. What was the composition of the earth's first atmosphere? What happened to it? What was the composition of earth's second atmosphere? Where did it come from?
  3. How do we know (a) the earth's mass, (b) the earth's age, and (c) the composition of the core?
  4. Consider 238U, which has a half-life of 4.5 Gyr. If this isotope of uranium crystallized into a rock about the time the earth formed, how much of the original remains today? How much will remain 4.5 Gyr from now? Answer: half will remain today, and 1/4 will remain 4.5 gyr from now (half of half).
  5. Argue from a comparison of average densities that the moon cannot have a metallic core like the earth?s, that Mercury should have a metallic core, and that the core of Venus should be most like the earth?s.
  6. What specific evidence do we have that the moon's lowland regions (maria) formed after the highlands? 1. Maria have few craters compared to the highlands and so must have a younger surface. 2. Direct age-dating of lunar rock samples confirms this.
  7. Mariner 10 photographed only about half of Mercury?s surface. Imagine that in the future a new flyby mission photographs the rest. It finds a region almost devoid of craters. What statements could you make about the age and history of this region? Either this region somehow avoided getting hit by debris (unlikely) or it was geologically resurfaced after the epoch of cratering was mostly over. Since that was a long time ago (3.5 to 4.0 Gyr) we can't say much about the absolute age of the rocks in this region, but they definitely congealed after the cratering epoch.
  8. How does it happen that the earth has two tidal bulges, one on the side facing the moon and another on the opposite side of the earth? You may draw a sketch if it will help you to explain. Not a lot of people answered this one very well. Forget rotation or motion of any kind. This is a simple application of Newton's gravity formula, where different parts of the are at different distances from the moon, and gravity varies as the inverse square of distance. Compared to the average force, the near side feels more gravity and the far side feels less, so a fluid earth will be pulled both directions, causing two bulges.

Homework 8

Due Dec 4

Research either the ozone hole problem or the global warming issue. Write a 500 word summary. In it, clearly define the chemistry and physics of the problem before writing of any sociopolitical ramifications.

Cite your sources! For example:

Most of the methane in the atmosphere is due to digestive processes in large ruminants such as domestic cattle (G. Seenan, The Guardian, 2003 March 1, Guardian Newspapers Limited) -or- (http://www.epa.gov/rlep/sustain.htm, U.S. Environmental Protection Agency).


Include all information a person might need to find the exact source you cite. If citing web resources, please stick to edu or gov sites (a good policy in general if you want nonslanted factual information).

Homework 9


Due Dec 11. Answer on separate sheets.

  1. Edwin Hubble measured the brightnesses of Cepheid variables in as many galaxies as he could (not many!) and also secondary distance indicators such as bright clumps of OB stars and computed distances to the galaxies. He found that the more distant galaxies had larger redshifts and hence larger velocities away from us. Write the formula that describes this effect and define the terms in the equation.
  2. Assume that H0 = 65 km/s/Mpc.
    a. What is the expected recessional velocity of a galaxy 10 Mpc away?
    b. About how far away is a galaxy with velocity 6500 km/s?
    c. How far away is a galaxy with velocity 130,000 km/s?
  3. What is the meaning of the Hubble Law? Are galaxies in back of us flying away from us too? Does this mean the Milky Way is at the center of some cosmic disturbance?
  4. Classify the galaxies at http://astro.wsu.edu/worthey/astro/html/lec-tuning.html on the Hubble "tuning-fork" classification system, and give brief reasons for your choices.
  5. Two major observations make the "Big Bang" picture the one that best explains the facts. What are they?