Classical vs. Cosmological Redshift LAB 

For this lab, you’ll use the following lab write-up as a template. Record 

your answers to each question and activity this document, and upload 

as a .doc or .pdf document to the following module item for grading:

“Classical vs. Cosmological Redshift Lab Submission”

1) Write a paragraph or two summarizing what you learned from the 

background information. Include anything you found interesting, 

and propose how you think this information would be helpful in 

astronomy and astrophysics.

2) Consider the following formula:

Here z is the redshift and the lambdas represent the observed and 

emitted wavelengths for the light in consideration. What does a 

redshift of zero mean? What does a redshift of one mean? How 

many times longer is the observed wavelength than the emitted 

wavelength if the redshift is seven?

3) Consider the following link:

https://lco.global/spacebook/distance-and-lookback…

The lookback time tells us how long the light has taken to reach 

us. Why is this not equal to the current distance to the galaxy?

In order to calculate the current distance to the galaxy, several 

assumptions about the Universe must be made. How fast is the 

Universe expanding? Has it always been expanding at this rate?

These are questions beyond the scope of this lab.

4) In astrophysics we assume that there is no preferred spot in the 

Universe and that the laws of physics are the same everywhere in 

the Universe. As a result, we would expect objects to be moving 

randomly throughout space.

Let’s assume that all of the galactic motion in the Universe is 

classical in nature. What would we expect to see as far as redshift 

and blueshift are concerned? Would this change in any significant 

way with distance? Why or why not?

Now assume that all of the galactic motion in the Universe is 

cosmological in nature. What would we expect to see as far as 

redshift and blueshift are concerned? Would this change in any 

significant way with distance? Why or why not?

5) In reality the galactic motion in the Universe is a mixture of the 

two. Consider looking at galaxies with several different redshift 

values. Consider the following two cases:

a. Classical motion dominates over cosmological motion. The 

magnitude of the random velocity is greater than the 

magnitude of the recessional velocity. Now what would we 

expect to see as far as redshift and blueshift are concerned? 

Would this change in any significant way with distance? Why 

or why not?

b. Again repeat, but now assume that cosmological motion 

dominates over classical motion. The magnitude of the 

recessional velocity is greater than the magnitude of the 

random velocity.

6) Consider that light was emitted from a galaxy with a wavelength 

of 2.50 * 10

-10

meters. What would be the observed wavelength 

for the following redshifts?

a. 0.05

b. 0.25

c. 0.60

d. 1.0

e. 2.0

f. 4.0

g. 8.0

7) Assume that visible light is in the range of 400 nanometers to 700 

nanometers. Which of the above would result in observations 

being made in the visible light spectrum?

8) Write a two paragraph conclusion of what you have done. Include 

any results that may have surprised you.

PLEASE SEE THE ATTACHMENTS !!