Galaxies are made of billions of stars in a huge group. Scientists estimate that the largest galaxies may contain as many as a trillion stars. The smallest galaxies may contain at least less than a million stars.
Shapes of Galaxies
Scientists class galaxies by their shape. There are three general shapes. This method was suggested by an American astronomer, Edwin Hubble, in 1925. The three kinds of galaxies are elliptical, spiral, and irregular.
An elliptical galaxy is a galaxy that shows little or no structure. In other words it looks like a squashed ball.
A spiral galaxy is a galaxy that has a small, bright central nucleus and winds around, like a pinwheel.
An irregular galaxy has no specific shape or size.