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East Los Angeles College *
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Course
101
Subject
Astronomy
Date
Dec 6, 2023
Type
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2
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Q1: Look at your results from Step 6 (distance column in Table 1) above. What, if
anything, can be said about the distances of stars that didn't seem to move from image #1
to image #2? [For example, "they must be closer than
....
" or "they must be farther away
than
....
" Fill in the blank with a number.
A1: Stars that didn't seem to move from image #1 to image #2 must be farther away than the
maximum measurable parallax. If the smallest measurable shift is, for example, 0.1 arc-seconds,
then stars with no measurable shift would be farther away than 1/0.1 = 10 parsecs.
Q2: Suppose you observed the same field of stars 3 months after image #2 was taken.
Describe in words how you would expect the positions of stars to appear. Include a sketch if
that would help explain what you would see.
A2: Assuming a continuous observation, stars would continue their apparent motion due to
Earth's orbit. If the second observation is 3 months after image #2, the stars that appeared to
move in the first set of images would continue to shift in the same direction. Stars that seemed
stationary in the first set might now exhibit a measurable parallax.
Q3: Suppose you observed the field once more 9 months after image #2 was taken. Describe
in words how you would expect the apparent positions of stars to compare to those
observed in image #1 and/or image #2.
A3: The apparent positions of stars would continue to change due to Earth's orbit. Stars that
moved in the first set of images would have shifted further, and those that appeared stationary
might now show a measurable parallax. The pattern of motion would be consistent with the
orbital period.
Q4: Put aside the images you've been working on for a moment. Imagine that all the stars
in the galaxy have the same intrinsic brightness, like light bulbs all of the same wattage.
Stars would then appear brighter or fainter depending on whether they were relatively
close or relatively far away from the Earth. If this were the case, which stars would appear
brighter as seen from Earth: those with large parallaxes or those with small parallaxes?
Explain.
A4: In this hypothetical scenario, stars with large parallaxes (closer stars) would appear brighter,
as they are relatively closer to Earth. Parallax is inversely proportional to distance, so stars with
larger parallaxes would be closer and thus appear brighter.
Q5: Now consider the results of your analysis of the two images. Are the results consistent
with the hypothesis that all stars in the Galaxy have the same intrinsic brightness? Why or
why not? If not, give at least one specific example from this exercise that proves your point.
A5: The results are not consistent with the hypothesis of all stars having the same intrinsic
brightness. The apparent sizes of stars in the images are determined by their brightness, not their
actual dimensions. In this exercise, stars that appeared to move (indicating a measurable
parallax) have varying distances, and their brightness does not follow a consistent pattern. This
inconsistency in brightness among stars with measurable parallaxes contradicts the assumption
of uniform intrinsic brightness for all stars in the galaxy.
NAME
| Amount of Shift (mm) | Parallax (Arcsec) | Distance (parsecs) | Distance
(Light-years)
-------------------------------------------------------------------------------------
Star 1
|
0.5
|
5.0
|
0.2
|
0.65
Star 2
|
1.0
|
10.0
|
0.1
|
0.33
Star 3
|
0.2
|
2.0
|
0.5
|
1.63
-------------------------------------------------------------------------------------
Step 8:
Smallest possible measurable shift:
|
0.1
|
Smallest possible measurable parallax:|
1.0
|
Distance to star for which a parallax could just barely be measured:|
1 pc
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