Starship Asterisk*

Galaxies come in a variety of sizes and shapes. They can have as few as 10 million stars or as many as 10 trillion (the Milky Way has about 200 billion stars). In 1936, Edwin Hubble classified galaxy shapes in the Hubble Sequence.

1) Elliptical: These have a faint, rounded shape, but they're devoid of gas and dust, with no visible bright stars or spiral patterns. They also don't have galactic disks, which we'll learn about below. Their classification varies from E0 (circular) to E7 (most elliptical). Elliptical galaxies probably comprise about 60 percent of the galaxies in the universe. They show wide variation in size -- most are small (about 1 percent the diameter of the Milky Way), but some are about five times larger than the diameter of the Milky Way.

2) Spiral: The Milky Way is one of the larger spiral galaxies. They're bright and distinctly disk-shaped, with hot gas, dust and bright stars in the spiral arms. Because spiral galaxies are bright, they make up most of the visible galaxies, but they're thought to make up only about 20 percent of the galaxies in the universe. Spiral galaxies are subdivided into these categories:

S0: Little gas and dust, with no bright spiral arms and few bright stars

Normal Spiral: Obvious disk shape with bright centers and well-defined spiral arms. Sa galaxies have large nuclear bulges and tightly wound spiral arms, while Sc galaxies have small bulges and loosely wound arms.

Barred Spiral: Obvious disk shape with elongated, bright centers and well-defined spiral arms. SBa galaxies have large nuclear bulges and tightly wound spiral arms, while SBc galaxies have small bulges and loosely wound arms (recent evidence suggests that the Milky Way is a SBc galaxy).

3) Irregular: These are small, faint galaxies with large clouds of gas and­ dust, but no spiral arms or bright centers. Irregular galaxies contain a mixture of old and new stars and tend to be small, about 1 percent to 25 percent of the Milky Way's diameter.

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.