Classifying Galaxies
Pretend that you are an astronomer working shortly after Edwin Hubble
made his startling discovery. Now that you know the "nebulae" are actually
other galaxies like our own, you must come up with a way to classify the
galaxies.
Exercise
1: Look at the following galaxies. Divide them into groups
based on features they have in common. There is no set number of
groups.
Use the
Get Fields
tool to look up each galaxy. SDSS images are sorted by regions of the
sky, into runs, camera columns (camcols), and fields. The list below
shows what run/camcol/field area each galaxy is in. Click on each galaxy's field
number to see a picture of the field. Because galaxies
tend to cluster together, some of the frames have more than one large
and interesting galaxy, but in all the other
frames, the largest galaxy should be obvious.
 |
A unique SDSS
galaxy |
Run |
Camcol |
Field |
752 |
1 |
244 |
2662 |
4 |
243 |
752 |
1 |
331 |
1737 |
6 |
11 |
756 |
4 |
198 |
2738 |
2 |
196 |
752 |
1 |
432 |
3325 |
3 |
176 |
3325 |
3 |
319 |
3325 |
2 |
216 |
3325 |
2 |
215 (just left of center) |
3325 |
3 |
230 (2 galaxies) |
2738 |
3 |
122 (2 nice galaxies) |
3325 |
3 |
352 |
3325 |
1 |
356 |
3325 |
1 |
359 |
|
Now, find another group and partner up with them to compare your
results.
Question 1: Do
you have the same number of galaxy classes as the other group? If not, what distinctions
did one group draw that the other did not? |
Question 2: What
do your classification systems have in common? What makes them
different? |
Question 3: Try
to combine the best features of each classification system. Repeat
Exercise 1 with your new system. |
The first person to classify galaxies was Edwin Hubble. He looked
at pictures like those you saw, although his pictures were not nearly
as clear as yours!
Hubble saw many of the same types of galaxies that you did. In the next
few pages, you will learn a little about the types of galaxies that
both Hubble and you saw. Then you'll learn about the classification system
that Hubble developed, which astronomers still use today. |
