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21A: Astronomical Spectroscopy
How is spectroscopy used in astronomy? What can it tell us?
We have already seen how spectroscopy can help us identify
elements, or even identify compounds with multiple elements.
Spectroscopy can also be used to tell us many things about the
universe around us. We can learn about the composition of
distant stars, determine the approximate age of stars, and even
analyze what compounds exist on faraway planets. Spectroscopy
is helping us to determine whether life can exist in outer space! In
this investigation, you will learn how spectroscopy is used in
astronomy.
Materials
• Element spectroscopy cards
(1 set per group)
• Star spectroscopy cards
(1 set per group)
Part 1: The elemental composition of stars
a.
Look at the element spectroscopy
cards. Notice that they are emission
cards, that is, they show the colors
that those elements emit when they
are excited. What creates these
emission lines?
b.
Now look at the astronomical
spectroscopy cards. Notice that they
are absorption cards, that is, they
show which wavelengths of light are
absorbed in the star. This is because
the hot plasma in stars emits all
wavelengths of light, and the
elements in the star absorb the same
characteristic wavelengths of light.
(Remember your experiments with
the Lab-Master spectrophotometer?)
The star produces all wavelengths of
light in its core from fusion. Where in
the star is its absorption spectrum
created?
c.
Compare the element cards to the star cards. What similarities do you notice?
d.
Determine which elements are present in each star by matching the emission lines on the element
cards to the absorption lines on the star cards.
e.
As stars burn, they convert lighter elements to heavier ones by nuclear fusion. Rank the stars on the
star cards from youngest to oldest based on this information.
f.
Notice that some elements are half-shaded in. What do you suppose this means in terms of the
amount of that element in the star?
A NATURAL APPROACH TO CHEMISTRY
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Investigation 21A:
Astronomical Spectroscopy
Part 2: The temperatures of stars
a.
Notice that each star spectroscopy card also has a “blackbody spectrum.” This spectrum shows the
intensities of each color of light coming from each star.
b.
What temperature corresponds to the hottest stars? What temperature corresponds to the coldest
stars?
c.
Rank the stars from hottest to coldest.
d.
What similarity do you notice between your two lists? Why do you suppose that is?
e.
One star should not fit this pattern. Which one is it? Research online why this star is different from
the others. You should find some interesting information about what this star will be doing very soon.
f.
(Optional) The graph below is called the Hertzsprung–Russell (HR) diagram. Do some research
online about this diagram and about the stars we have studied in this investigation. Place Rigel and
the other stars on the diagram. Which of the stars that you studied is the hottest?
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A NATURAL APPROACH TO CHEMISTRY