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Kinds of galaxies

Astronomers describe galaxies by their shape. Most galaxies have one of three shapes, elliptical, spiral, or irregular. An elliptical galaxy has an egg-like shape. A spiral galaxy is flat, with arms that wind around a ball-like center. An irregular galaxy may have some shape or seem to have none at all.

Hubble sequence

The Hubble sequence. An E is an elliptical galaxy, an S is a spiral galaxy and a SB is a barred spiral galaxy.

In xxxx Edwin Hubble invented a way of grouping galaxies using their shapes on photographs. This is called the Hubble sequence. (A sequence is an ordered list.) The elliptical galaxies are on the left side of the picture. The spiral galaxies are on the right side, in two lines. The bottom line is for barred spiral galaxies. These galaxies have a bar-shaped line of stars at their center.