Some stars at the time of their formation coagulated into two separate bodies revolving around their common center of gravity. The two stars are often very different—one vast, one tiny; one dense, one diffuse; close together or far apart and often radiating different colors. Life on a planet orbiting the double star Alpha Herculis, for example, would be very strange—two suns in the sky, one red and one green.

GL105A and C (HD 16160), HST, courtesy NASA