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AST 201 MIDTERM ASSIGNMENT
Instructions
The AST 201 MIDTERM ASSIGNMENT has two separate parts. Part 1 of the assignment is
the timed on-line quiz (see Quercus for details if you have not completed Part 1 already). Part 2,
featured below, is a series of short answer questions to be answered using the form provided on
Quercus and uploaded to Quercus by March 4, 2022 at 11:00 am EST.).
Honour Statement:
I ____________ acknowledge that this assignment was completed by me and me alone, with
only the aid of AST 201 Course Materials (lecture and tutorial slides, the textbook, my personal
notes). I am aware that obtaining or providing assistance on this assignment from another source,
including my fellow students
Signed: ________________________
1
Part 2: Short Answer Questions
Fill out the answers to these questions using the form available on Quercus.
Question 1:
a) You are traveling in a spaceship, headed towards Earth, and you hold a ball at arm’s length.
When you let go of the ball it falls to the floor as shown in Figure 1. What does this obser-
vation tell you about the acceleration of the spaceship? [2 marks - approx 200-400 words]
b) If you shine a white light out of the window of the spaceship towards Earth. At what speed
will the light appear to travel and why? [1 mark - approx 100-200 words]
c) What colour will the light appear to be to observers on Earth, and why? [1 mark - approx
100-200 words]
Figure 1: The setup for your ball-dropping experiment on the spaceship in Question 1.
2
104 2×1033×1034×1036×103
Temperature (K)
10 4
10 2
100
102
104
L/
L
Figure 2: Luminosity and temperature of individual stars that you observed with your telescope.
Question 2:
Due to your amazing performance in AST 201, a brand new telescope has been named after you.
It is therefore only fitting that you get to make the very first set of observations. During your first
night observing, you first measure the apparent brightness and spectrum of a group of stars that
appear close to each other within the telescopes field of view. From a separate set of observations
6 months later you are able to measure each star’s parallax. Next you plot the luminosity and
temperature of each star in a Hertzsprung-Russell Diagram (see Figure 2).
a) What features in Figure 2 help you conclude that the group of stars is a star cluster? Explain
your reasoning. [2 marks - approx 100-200 words]
b) Approximately how old do you think this star cluster is? Explain your reasoning. [2 marks -
approx 100-200 words]
c) How do you expect the spectrum of the most luminous and least luminous main sequence
stars in the cluster to differ. Explain why these differences occur in terms of the star’s prop-
erties and any measured absorption lines. [4 marks - approx 200-400 words]
d) A year after your discovery, another new star cluster has been found by the same telescope,
but its distance is too far to be measured by parallax. What alternative methods could be
used to measure the distance to this new cluster. [4 marks - approx 200-400 words]
3
Question 3:
Figure 3 shows the spectra of two objects observed with a new telescope.
a) For each object (A and B), state if it is a star and why or why not? [2 marks approx 200-400
words].
b) If Object A cooled (while staying the same size), what would happen to the brightness and
colour of the star. [2 marks approx 200-400 words]
Figure 3: Spectra of two objects observed with a new telescope.
4
Question 4:
You are shocked to learn that the Sun (which has a mass of 1M⊙) and Betelgeuse (with a mass of
11M⊙) have both become black holes overnight.
a) Which black hole would have a larger event horizon and why? [1 mark - approx 100-200
words].
b) What do you experience if you fly your spaceship towards the Betelgeuse black hole? De-
scribe any effects on you or the spaceship [2 marks - approx 200-400 words].
c) What would an observer on the other side of the galaxy see when looking at the black holes
against the background of the rest of the stars in the Milky Way? [1 mark - approx 100-200
words].
