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Prepared by Gilberto Berríos
May 2, 2008
Reading Selections for ID1113, p. 10
Pre-reading activity
After reading the introduction, answer the following questions.
1. What is the Doppler Effect?
The change in wavelength perceived by an observer who moves with respect to the wave source
2. What phenomena are related to the Doppler Effect?
The so-called blueshift and redshift
3. What is the connection between the Doppler Effect and the universe?
That we can perceive the direction of universe motion by looking at the spectra of stars
Reading Selections for ID1113, p. 12-14
Working with the text
Read carefully the following topics and indicate the number of the paragraph where they are stated:
M. Humason’s story
Explanation of the red-shift of galaxies
Doppler Effect and sound
M. Humason and E. Hubble’s discoveries
Doppler Effect and light
M. Humason and E. Hubble’s relationship and work
1. Match the words in column A with their corresponding equivalent in column B.
1. to be used to (par. 1, line 2)
a. moving back, becoming distant
1. _g__
2. stretch out (par. 1, line 8)
b. lengthen
2. _b__
3. figure out (par. 4, line 5)
c. consternation
3. _e__
4. nearby (par. 5, line 6)
d. running away, flying, escaping
4. _f__
5. amazement (par. 5, line 7)
e. understand, solve
5. _c__
6. receding (par. 6, line 2)
f. adjacent, neighboring
6. _d__
7. fleeing (par. 6, line 3)
g. to be familiar with
7. _a__
Prepared by Gilberto Berríos
May 2, 2008
2. Complete the following summary of the text using the words form the chart below.
Working in Mount Wilson, Humason and Hubble found that distant galaxies are red-shifted and
interpreted this in terms of the Doppler Effect: galaxies are receding from us; the more distant
galaxies are receding faster than the near ones in proportion to their distance. This discovery led
to the notion of the expansion of the universe and to the Big Bang theory.
Understanding the text  these two questions are too difficult for me; we’ll comment on them
Choose the best alternatives to complete the following statements.
1. The Doppler Effect in astronomy can be used to explain __b__.
a. the movement of galaxies away from the Earth  I also think this is an answer
b. the expanding movement of the universe  best answer; see paragraph 6
c. the gravitational attraction of stars
2. This text can be seen in terms of:  Perhaps the question should be, “This text presents…”
a. a suggestion of a new hypothesis.
b. a restatement of accepted theories.
c. a rejection of a hypothesis.
After reading activity
Answer the following questions.
1. Why are galaxies said to be red-shifted?
Because they have red light spectra, suggesting that they are withdrawing from us (according to a
Doppler effect interpretation).
2. What would happen if the light from a galaxy were blue-shifted instead of red?
It would mean that the galaxy is approaching us.
3. Why is the red shift of galaxies used in support of the Big Bang theory?
Because it shows that galaxies are moving away from us and thus supports the idea that they were
closer together in the past.
4. How does the expansion of the universe fit into the Big Bang theory?
The expansion is a consequence of the initial explosion.