The Hubble Tuning Fork
In the early 1900s, Edwin Hubble looked at galaxies like the ones
you saw in the last few pages. Hubble classified the galaxies using
a "tuning fork" system. The
elliptical galaxies made up the fork's handle, and spiral galaxies and barred
spiral galaxies make the fork's prongs. So his classification system looked
like this:
Hubble believed that galaxies started at the left end of the tuning
fork when they were young, and moved toward the right as they aged.
Therefore, he called elliptical galaxies "early galaxies" and spiral
galaxies "late galaxies".
We now know he was mistaken in this
belief. Spiral galaxies have a great deal of rotation and elliptical
galaxies do not. There is no way an elliptical galaxy could
spontaneously begin rotating, so elliptical galaxies cannot turn into
spiral galaxies. Although Hubble was wrong about his
theory of galaxy evolution, the confusing names have stuck:
today, elliptical galaxies are still referred to as
early galaxies and spirals as late galaxies.
Exercise 2.
Go back to the galaxies
from Exercise 1, shown again in the table below. Click the field
numbers to see pictures of the fields. Classify all the galaxies on
the Hubble Tuning Fork. Use this
SkyServer workbook to keep track of your work.
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 |
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Question 4.
Compare and contrast your classification system to Hubble's.
How are they similar? How are they different? |
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