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School
University of British Columbia *
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Course
311
Subject
Astronomy
Date
Jan 9, 2024
Type
Pages
4
Uploaded by CorporalAtom403
ASTR 311 — Tutorial 6
Distances and the Expanding Universe
1
Think about It!
Overview:
Accurately measuring distances to astronomical objects is one of the key challenges astronomers face today. Many
methods can be used to determine cosmic distances; however, each method can be accurately employed only over a specific
range.
Procedure:
For each object, list the method for determining cosmic distances that would provide the most accurate measure
of the distance. Explain why you chose the method you did.
1. The Sun
2. Venus
3. Faintly visible red dwarf main-sequence star
4. Moderately bright spectral type F1 main-sequence star
5. Globular cluster orbiting the Milky Way
6. Irregular galaxy in the Local Group
7. Galaxy at the far edge of the Virgo Cluster
8. Large spiral galaxy in a distant supercluster
9. Proto-galaxy discovered in Hubble Space Telescope Ultra Deep Field image
2
Experiment!
In this part you are going to learn about the expansion of the universe and how it is inferred from observations.
Nearby galaxies on Wednesday
Nearby galaxies on Friday
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
1. Choose one galaxy to be your home galaxy. Use your first initial, for example. Be sure that your partners choose other
home galaxies.
2. Measure the distance between your home galaxy and the other galaxies on Wednesday and Friday and complete the
following table.
Galaxy
Distance on Wednesday (
d
W
)
Distance on Friday (
d
F
)
d
F
-
d
W
3. Plot the difference in distances
d
F
-
d
W
as a function of
d
W
on the following grid.
d
W
[cm]
d
F
-
d
W
[cm]
4. Connect the points with a line drawn along the ruler.
5. What is the slope of the line? That is, if you increase
d
W
by 1 cm, how much does
d
F
-
d
W
increase?
6. What slopes did your partners get? (if you have partners)
7. On which day of the week did the Universe begin in this example?
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3
Think Some More!
Overview:
The Big Bang theory is widely accepted by astronomers today because it has been supported by multiple different
pieces of observational evidence. In this activity, you will consider a few of the key pieces of evidence in favor of the Big Bang.
Procedure:
Work through the questions below with your group, then record your final answers.
1. Why do astronomers say that we are “seeing” the Big Bang with observations of the cosmic microwave background?
Explain how such observations are powerful evidence in support of the Big Bang theory.
2. When astronomers measure the abundance of atomic elements in what appear to be isolated and untouched parts of
the universe, they always detect the same amounts of hydrogen and isotopes of helium and lithium. Explain why these
observations are powerful evidence in support of the Big Bang theory.
3. The chains and sheets of galaxies and voids between them observed in the large-scale structure of the universe were once
thought to be inconsistent with the Big Bang theory. Explain why these observations are now considered to be evidence
that supports the Big Bang theory.