Class 18, 3/9/04

Hightlights

N1: the cosmic distance ladder
* We already had a glimpse of it before. See Quiz 1, problem 5. And see Fig. 20.21.
* First we discussed how Erotasthenes (about 240B.C.) measured the circumsference of the earch using simple trigonomitry. See Special Topic on p. 65 of TB1. So, the circumsference of the Earth, 2pi R_ea = d_a-s x (360 / 7), where d_a-s is the distance between Alexandria and Syene that sustain an angle of 7 degree of the wedge from the center of the earth to the two places.
* We than follow the steps indicated in Fig.20.21; Attachment to HW2; and Quiz 1, problem 5:
    ** Step 0, up to 10^-4 ly (the solar system): trigonomity and/or radar ranging;
    ** Step 1, up to 10^2 ly (near by stars): parallax (see Fig. 16.3);
    ** Step 2, up to 10^5 ly (Milky Way): Main-Sequence fitting (using the H-R diagram; see Fig.16.10, and Fig. 20.11).
    ** Step 3, up to 10^7 ly (near by galaxies): Cepeids variables (using their brightness/period relation established in the galaxies whose distances were well establised in the previous steps);
    ** Step 4, up to 10^10 ly (galaxy clusters);
    ** Step 5, up to R_ob, the radius of the observable universe. (Remember to review the definition of obserbable U. See Quiz 1, solution to Promlem 1.)

* For each step, we viewed animations and figures to explain the concepts involve.

N2: The age of the universe (cosmic age) is nothing but (approximately equal to) the inverse of the Hubble constant,
        T_U = 1/H_0 = 1.4 x 10^ 10  yr.
 * See, section 20.4 of TB1, and HW2, SA2.2.

N3: Coninuing the three connecting topics started earlier: Minkowski thm, wave properties of particles, and uncentainty relations. We will complete the discussion in the next lecture.
   


Preview

* We will discuss and almost finish the following material,

Week-9 (3/4 -3/11 ) reading assignment:
  · Properties of Stars, & Cosmic Distance and Age,  Read Chpt 16,  p.521-542; and part of Chapt 20, p. 632 -648, of TB1.
  · Fig. 17.26 & its explanations.

* At the end of the class, graded Quiz 3, its statistics, graded HW8, solutions and all scores will be distributed.


Please read the following before you fill out the sign-up sheet.

( Please try to review the class web page and have the answers ready before class.)

Sign-up items, Class 18, 3/9/04

(1) Have you finished reading the following reading assignments?   Y, P (partial), or N.
    Week-9 (3/4 -3/11 ):
  · Properties of Stars, & Cosmic Distance and Age,  Read Chpt 16,  p.521-542; and part of Chapt 20, p. 632 -648, of TB1.
  · Fig. 17.26 & its explanations.
(2) Initial.