Name________________________________________
Classifying Stellar Spectra
We have learned that astronomers classify stars by their spectra. The particular spectral
class of a star tells us the star's surface temperature. In this activity, you will take part in a
project called Stellar Classification Online Public Exploration (SCOPE).
Follow the directions below to take part in the project:
1. Open a browser and go to: scope.pari.edu
2. At the top of the page, click the "The Science" link and read all of the information
on the page. You do not need to click the “MORE” links.
3. At the top of the page, click the "To Take Part" link and read all of the
information on the page.
4. At the top of the page, click on the "Classify" link. Click on the "Click here to
register" link under the login box and create an account.
5. Login to your SCOPE account and classify stars until you have found a total of 4
main-sequence stars. To do this, follow the detailed directions on the next page on
how to use the classification tools. **Note, you may have to classify more than 4
stars to do this because some of the stars you encounter may be Red Giants or
White Dwarfs. Remember, main-sequence stars have the luminosity class, V. So,
if the star is a main sequence star, it’s spectral type will be something like A5 V
or G2 V. If the spectral type has any other roman numeral at the end (F3 I or M2
III for example), then it is not a main-sequence star. Once you have found 4
main-sequence stars, record their names and spectral types in Table 1 on the last
page of this activity. To see all the stars you’ve classified, you can click on the
“My Stars” button in the toolbar at the top of the SCOPE webpage.
6. Finally, use Table 2 to determine the surface temperatures of your 4 mainsequence stars. Record the temperatures in Table 1.
7. Take a screenshot of your “My Stars” page on SCOPE to submit along with this
activity.
Using the classification tools:
 Once you login and click the "Classify" button at the top of the screen, you will
be presented with a list of photographic plates to choose from. Go through the list
and just pick a plate at random.

A window with the photographic plate will open up. Scroll down along the
photographic plate. Pick one of the spectra that is outlined in blue. When you
click it, the blue outline should turn yellow. Then, click OK.

At the top of the screen is the unknown spectrum you are trying to classify and on
the bottom part of the screen are the main categories of spectra (OBAFGKM) you
will use for comparison. If you double-click on one of the comparison spectra, it
will put this spectrum in the "Place-Holder" area just above the unknown
spectrum.

You can use the + and - magnifiers to stretch the spectra out, and you can use the
green arrows to shift the comparison spectrum left and right to help line it up with
the unknown spectrum. Try to find the comparison spectrum that most closely
resembles the unknown spectrum.

Now, to refine the classification, click on the "View Next Level" button. You
will notice that the main categories of comparison spectra are replaced with finer
sub-categories of spectra. Use these more detailed spectra and find the one that
most closely resembles the unknown spectrum.

Once you have the comparison spectrum that most closely matches the unknown
spectrum, go to the top of the window and click the "Save the Classification"
button. This will open a new page in your original browser window. Click the
"Record" button to record your classification. You have now classified a star!

Repeat this process until you have found 4 main-sequence stars.
Table 1 – Main Sequence Stars Classified Using SCOPE
Star Name
Spectral Type
Temperature (K)
Table 2 – Surface Temperatures of Main Sequence Stars
Spectral
Type
O5
O6
O7
O8
O9
B0
B1
B2
B3
B5
B6
B7
B8
B9
A0
A1
A2
A3
A4
A5
A7
F0
F2
F3
F5
F6
F7
F8
Temperature
(K)
54,000
45,000
43,300
40,600
37,800
29,200
23,000
21,000
17,600
15,200
14,300
13,500
12,300
11,400
9600
9330
9040
8750
8480
8310
7920
7350
7050
6850
6700
6550
6400
6300
Spectral
Type
G0
G1
G2
G5
G8
K0
K1
K2
K3
K4
K5
K7
M0
M1
M2
M3
M4
M5
M6
M7
M8
Temperature (K)
6050
5930
5800
5660
5440
5240
5110
4960
4800
4600
4400
4000
3750
3700
3600
3500
3400
3200
3100
2900
2700