Lydia Baker - Spectral Lines Gizmo Digital
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School
Rockingham Community College *
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Course
131
Subject
Astronomy
Date
Apr 3, 2024
Type
docx
Pages
4
Uploaded by CorporalIron13450
Name:
Lydia Baker
Date:
3-29-22
Student Exploration: Star Spectra
Directions: Follow the instructions to go through the simulation. Respond to the questions and prompts in the orange boxes.
Vocabulary:
absorption spectrum, binary star, blueshift, Cepheid variable, emission spectrum, giant star, nebula, redshift, spectrum, star
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1.
What happens when light goes through a prism?
the light reflects off of different things giving different colors
This band of colors is called a spectrum
. 2. A rainbow is an example of a spectrum. What is the sequence of colors in a rainbow? Red Orange Yellow Green Blue Indigo Violet
Gizmo Warm-up
The interior of a star
produces a continuous spectrum of light, like a rainbow. Cooler gases in the outer layers of the star absorb certain wavelengths of light, causing dark lines to appear in the spectrum. The resulting absorption spectrum
can tell astronomers a great deal about the star.
1.
On the Star Spectra
Gizmo, turn on Show labels
. Select star 1
to see its absorption spectrum.
How many lines do you see in the spectrum? 10
2.
Drag the Hydrogen
spectrum next to the Star spectrum so that the edges line up. Do some of the lines on
the two spectra match up? some do, some dont
3.
Drag the Helium spectrum next to the Star spectrum. Do some lines match?
helium lines up with star spectrum
4.
Try out the other available spectra. Do any others have lines that match?
no
5.
Which elements have contributed to the spectrum of star 1? Helium and Hydrogen
Note: The elements in a star’s spectrum do not necessarily reflect what the star is made of. The absorption spectrum is mostly determined by the surface temperature of the star.
Activity A: Classifying stars
Get the Gizmo ready
: ●
Check that Show labels
is on and Neutral spectra
is selected.
Question: How are stars classified?
Introduction:
Late in the 19
th
century, Harvard astronomer Edward Pickering wanted to sort and catalog the thousands of star spectra that had been collected by the Harvard Observatory. He hired several women to do the work, paying them 25 cents a day. The most prominent of these women was Annie Jump Cannon, who devised a classification system still used today.
Harvard Classification Scheme
Class
Color
Prominent spectral lines
Surface Temp. (K)
O
Blue
Ionized helium, hydrogen
> 25,000
B
Blue-white
Neutral helium, hydrogen
11,000 – 25,000
A
White
Hydrogen, ionized sodium, ionized calcium
7,500 – 11,000
F
White
Hydrogen, ionized sodium and calcium; neutral sodium and calcium
6,000 – 7,500
G
Yellow
Neutral sodium and calcium, ionized calcium, ionized iron, ionized magnesium
5,000 – 6,000
K
Orange
Neutral calcium, neutral iron, neutral magnesium
3,500 – 5,000
M
Red
Neutral iron, neutral magnesium, and neutral titanium oxide (not shown)
< 3,500
1.
Classify
: Use the Gizmo to find the elements that are present in the spectra of stars 1 through 4. Remember to check both the Neutral spectra and the Ionic spectra
. Then use the table above to classify each star and describe its surface temperature. (Note: A star spectrum may not display lines of all of the elements typical of its spectral class.)
Star
Color
Elements in spectrum
Class
Surface Temperature (K)
1
Blue Hydrogen and Helium
O
> 25,000
2
Orange
Calcium, Iron and Magnesium
K
3,500 - 5,000
3
Blue Hydrogen and Helium
O
> 25,000
4
White
Hydrogen, sodium and calcium
A
7,500 - 11,000
Activity B: Unusual stars
Get the Gizmo ready
: ●
Select star 5
. Question: What else can we learn from stellar spectra?
1.
Observe
: Observe the spectra of stars 5 – 10. Identify the elements in each spectrum, and try to classify each star. If you notice unusual features in these spectra, describe them.
Star
Color
Elements in spectrum
Class
Unusual features
5
Yellow
None
G
double line like sodium, but moved
6
White
Iron and Titanium
M
magnesium doesn't work, it has more lines than the regular magnesium
7
Blue White
Helium and Hydrogen and?
B
Normal
8
Yellow
Sodium
and Calcium
G
light goes in and out, go up and down
9
White
Hydrogen, sodium and calcium
F
calcium did not match, but moved occasionally
10
Yellow
Sodium and Calcium
G
Normal
Match
: Write the number of the star or object that matches each description (only stars 6-10
). Then use this information to help you identify the elements and reclassify the stars in the table above.
3
High atmospheric pressures in a star cause spectral lines to be broadened, or “smeared out.” Giant stars
, which have relatively low atmospheric pressures, are characterized by many narrow spectral lines.
2
If a star is moving away from an observer, spectral lines are redshifted
, or shifted toward the red end of the spectrum. An approaching star is blueshifted
.
8
A star orbited by a large planet will move in a small circle. This will cause its spectrum to be slightly redshifted part of the time and blueshifted at other times.
4
Binary stars
are pairs of stars that orbit one another. Their presence is indicated by two spectra that shift in opposite directions. 6
Cepheid variable
stars change their brightness in a regular cycle. Gas pressure builds up, causing
the stars to expand quickly. When the pressure is released, the star contracts, and the intensity of
some spectral lines may decrease.
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7
A nebula
is an enormous cloud of gas and dust in which stars are born. Most nebulae produce an emission spectrum
, which is characterized by bright lines of color against a dark background. The bright lines in an emission spectrum correspond to the dark lines in an absorption spectrum.
Assessment Questions:
1.
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4.
5.