Lab 9 - Exploring Stars and Blackbodies
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Lone Star College, Tomball *
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Course
2423
Subject
Astronomy
Date
Dec 6, 2023
Type
docx
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4
Uploaded by artishared
Lab 9 - Exploring Stars as Blackbodies: Student Worksheet
Pre-Lab
Look at the image of star cluster
NGC 330 (credit:
ESA/Hubble &
NASA, J. Kalirai, A. Milone) and
compare it to the image of the
flame.
1. What similarities and
differences do you note
between both pictures?
2. Besides stars and flames, describe at least one other situation where you have seen
hot, glowing materials in your life.
Activity
Scientists refer to
blackbodies
as any object that is both a perfect absorber and a
perfect emitter of electromagnetic radiation. Stars are the closest approximation to
blackbodies in the universe, and they emit radiation of various frequencies.
1. Explore the
Blackbody Spectrum
PhET simulation for about five minutes. Complete
the table below.
Notice
What do you think this simulation is intending to
teach its users?
What have you learned?
Wonder
What questions do you have about the ideas
this simulation is trying to teach?
What confuses you?
Describe 3 things you noticed:
Describe 3 things you wonder:
2. How do the blackbody spectra compare across objects of different temperatures?
a. Complete this table below.
Light Bulb
Sun
Sirius A
Temperature (K)
Peak wavelength
(λ
max
)
Color of λ
max
Visible color
Overall Spectral
Power Density
b. Describe, in words, at least three different relationships among variables that
you have observed.
3. Some objects have peak wavelengths outside of the range of light that is visible to
the human eye. However, we are still able to see these objects with our eyes. Explain
how this is possible.
4. The Sun peaks in green wavelengths. Why does the Sun not look green to us? (If you
are uncertain, check out the “Single Bulb” screen of
Color Vision
PhET simulation).
5. Develop a mathematical expression (an equation) that relates
temperature
and
peak
wavelength
for a blackbody object that is emitting radiation, using the observed data.
Complete the table and graph below to organize your thinking.
Temperature
T (K)
Peak Wavelength
λ
max
(μm)
Final expression relating
temperature
and
peak wavelength:
Describe the expression above in words. As appropriate, describe the nature of any
constants, including their significance and units.
Post-Lab & Discussion
1. Apply your expression by selecting any temperature for a star that you did not previously
measure. Calculate the expected peak wavelength. (Show work).
Although stars look “still,” they are actually very much in motion with respect to the Earth (and
our solar system).
2. How might the diagram below look different if the star was coming
toward
us? If it was
moving
away
from us? Explain!
Peak
Wavelength
Temperature
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3. How might astronomers determine if a blue star is actually blue, or if it is simply blue-shifted
due to motion? (Feel free to explore the Internet to find out!)