AST 309 (46575) Fall 2003
Quiz 2: Study List

Review Sessions

Review sessions have been scheduled for the following times and places: Oct 30th (Thursday), 5-6:30PM in Garrison 1; Nov 3rd (Monday), 5-6:30PM in Geology 2.324. Bring your questions!

Be sure to bring your calculator and your astrolabe on the day of the quiz, as well as to the review session!

Reminder

You are reminded to make handwritten notes to yourself on one side of an 8.5x11-inch piece of paper, which you may consult during the quiz. These notes will count 10% of your grade. The quiz questions will emphasize your ability to reason and think, not memorize isolated facts, and the notes are intended to reduce your reliance on rote memorization. Your notes must be signed and attached to your quiz when you hand it in.

Study Questions

• Define Apparent Solar Time. Explain how it can be determined by direct measurements of the Sun. Explain how the Equation of Time results from the facts that the Earth's orbit is elliptical, and that the Ecliptic is tilted with respect to the Celestial Equator. Explain the difference between Local Apparent Solar Time, Local Mean Solar Time, Standard (Zone) Time, and Universal Time. List and explain the corrections that must be applied to convert between them. Be able to apply these conversions using your astrolabe.
  
• Define Sidereal Time. Explain how it can be measured from observations of the sky. What is it used for? Explain how Sidereal time is used as the practical method for determining Universal Time. If you know the Sidereal Time, and also the date of the year, explain how you would determine the Mean Solar Time. For example, if today's date is October 22, one months after the Autumnal Equinox, and it is 8 h Sidereal Time, what is the Local Mean Solar Time? (Use your astrolabe).
  
• Explain how the Pendulum works, using the law of conservation of energy. List and explain some ways that the pendulum can be improved as a timekeeping mechanism. Define the "Q" of a resonator such as the pendulum, and estimate the "Q" of a typical pendulum such as the one we investigated in class in terms of an actual experiment. (For example, suppose that the pendulum is a 2-second pendulum, and it takes 2 minutes for its swings to die down to 1/3 of the original. What would be the "Q" of such a pendulum?) Explain why the "Q" of a resonator is important for time keeping.
  
• Draw a block diagram of each of the clocks on the list below. The diagram should show how the components of the clock relate to each other, and should clearly explain the function of each component. Identify the component of the clock that is most critical to the accuracy and stability of the clock, and explain the physical principle of its operation. Estimate the accuracy and stability of the clock. Explain particular advantages and disadvantages that each clock may have. Here are some clocks that you should be prepared to discuss:

          Water Clock (Clepsydra) 
          Pendulum Clock 
          Quartz Crystal Oscillator 
          Ammonia Resonator 
          Cesium Beam Clock 
          Rubidium Clock 
          Hydrogen Maser Clock

• Define UT-0, UT-1 and UT-2. Explain how each system of time measurement is related to the next, and the physical reasons why the three differ from each other. Define UTC. Explain how "Leap seconds" are used to keep UTC in step with Earth rotation time (UT-2), and why this is done. Explain the role of the BIPM (Bureau International des Poids et Mésures) in regulating the international system of timekeeping.
  
• Explain how ancient eclipses and even more ancient coral reef deposits help us to learn about the history of the rotation of the Earth. Explain the nature of the evidence and why it gives us information about earth rotation in the past. Explain the physical reasons for the slowing down of the rotation of the Earth.
  
• What is Ephemeris Time (Dynamical Time)? How is it measured, in practice? Why was the measurement of Ephemeris Time based on the Moon, even though its definition is in terms of the Sun?
  
• For each of the following techniques or devices, explain the principle of its operation and how it is used to determine information about Earth Rotation or Time. Discuss the kinds of errors that the technique is subject to, and how they may be accounted for.

          Lunar Laser Ranging 
          Very Long Baseline Interferometry (VLBI)

• Explain the basic principles of navigation: How can one use astronomical measurements to determine latitude? Longitude? Distinguish between astronomical and geodetic (map) latitude. What was the Problem of Longitude? How did people propose that it should be solved (list and explain the principle of at least 3 methods)? How was it ultimately solved?
  
• Explain (a diagram would be very helpful) what a line (or circle) of position is. Show how, with two lines (or circles) of position, your location on the surface of the Earth can be pinpointed. Explain the basic idea of how a line (or circle) of position can be plotted, given an astronomical observation of the altitude or zenith distance of a star. Why might a third line (or circle) be needed to completely pinpoint ones location on the surface of the Earth?
  
• What is Loran-C? Explain how it works. How many Loran stations must you receive in order to obtain your position and the time from Loran? Explain why we need this many stations. How accurate is Loran-C in determining your position (rough error in meters), given the fact that the typical error in the time of receipt of the Loran signal is approximately 0.5 microseconds (millionths of a second)? [Recall that in a nanosecond--a billionth of a second--light travels about a foot.]
  
• What is GPS? Explain how it works. What is the minimum number of GPS satellites one must receive in order to obtain your postion and time using the GPS system? Explain why this is so. How accurately can civilians use GPS to determine their location? What factors limit the accuracy of GPS for civilian users? How accurate is GPS in position determination for those using military receivers? What techniques can civilians use in order to get very precise information from GPS despite the deliberate degradation that has been built into it for civilian use?
  
• Explain how the ratio of [235]U to [238]U can be used to estimate the age of the heavy elements in the Earth, i.e., how long ago it was when the supernova that produced the heavy elements in the Earth's crust blew up. About how long ago was that event? Suppose that the earth were one billion years old, and suppose it started with equal proportions of [235]U and [238]U. What would we expect the proportions of these isotopes to be today? Be able to do similar calculations.
  
• Describe each of the following dating methods and explain how it works: Explain the assumptions of the method, and how the validity of the assumptions can be checked. What kind of objects can be dated by each method? What do the various dating methods tell us that the age of the Earth, Moon, and meteorites is?

1. Carbon-14 dating method.
2. Uranium/Lead and Thorium/Lead [206]Pb/[238]U, [207]Pb/[235]U and [208]Pb/[232]Th;
3. Rubidium/Strontium Isochron ([87]Sr/[86]Sr versus [87]Rb/[86]Sr);
4. Potassium/Argon ([40]K versus [40]Ar).

• Explain how the H-R diagrams of globular clusters are used to estimate the ages of the most ancient stars in our galaxy. Explain how the cooling curves of white dwarf stars can be used to obtain the same information. Approximately what is the age of the oldest stars in our galaxy, according to these methods?