Classifying Stars
Pretend for a moment that you are an astronomer living in the early
20th century, before the OBAFGKM
star classification system was developed. You are one of the first astronomers
who ever looked at spectra of stars, and it is up to you to develop a
classification system.
The table below shows a list of the first stars you are trying to classify.
Look at their spectra and divide them into several groups. There
is no set number of groups you should try to achieve, and the groups do not
have to have equal numbers of stars (because not all types of stars are equally
common). If you find a spectrum that has
nothing in common with any of the others, a group of one is OK (but on the
other hand, 16 groups of one is probably not useful either!)
Spectra in the SDSS are sorted by Plate and Fiber number. Click the fiber
numbers below to go to the Object Explorer entry for each star. When you click
the first number, the tool will open in a new window; when you click another
number, the entry for the new star will appear in the same Object Explorer
window.
Once you have a star loaded into the Object Explorer, scroll down in the
left-hand frame and click "Spectrum." You will see a full-sized picture of the
star's spectrum. If you click "Print Page," you can print out the spectrum.
Plate |
Fiber |
Plate |
Fiber |
| 266/51630 |
21 |
266/51630 |
173 |
| 266/51630 |
275 |
266/51630 |
314 |
| 266/51630 |
365 |
266/51630 |
513 |
| 273/51597 |
2 |
498/51984 |
538 |
| 273/51597 |
157 |
273/51597 |
245 |
| 273/51597 |
589 |
281/51614 |
3 |
| 281/51614 |
4 |
281/51614 |
133 |
Exercise 1. Make a table as shown below. Classify the stars into groups, and record your groups in the table. Each star should fit
in one of your groups. Make notes detailed enough that another group
can duplicate your work. (You may have more than four groups or fewer
than four groups...this is just a sample chart!)
Group |
Star(s) |
Characteristics |
| |
|
|
| |
|
|
| |
|
|
| |
|
|
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Now, find another group and partner up with them. Compare your spectral
classification system to theirs.
Question 1. Do you have
the same number of spectral types as the other group does? If not, what
distinctions did one group draw that the other group did not? |
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Question 2. What do your classification systems have in
common? What makes them different? |
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Question 3. Try to
combine the best features of each classification system. Repeat
Exercise 1 with your improved system. |
You have just solved the same problem astronomers at the
turn of the century faced when they developed the technology to take spectra of
stars. If your classification system is different from the modern
one, don't worry. The original classification system underwent several revisions
before astronomers arrived at a
consensus. Originally, the classifications were the letters A
through P. As time progressed, some classifications were added, some
were dropped, and some were combined.
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