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# 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.

 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

 Question 4. Compare and contrast your classification system to Hubble's. How are they similar? How are they different?

Hubble tuning fork diagram courtesy of the Space Telescope Science Institute.