15 Constellations – A Summary
J. A. Hester
The stars are so extremely distant that their apparent direction in space does not change as the Earth spins, or even as it orbits around the Sun. They stay locked into fixed patterns. This lack of parallax is one reason that ancient astronomers concluded it was the stars and not the Earth that move. (Today, parallax is used in animation and video gaming to give a sense of depth and motion.)
Familiar patterns of bright fixed stars were grouped by many ancient cultures into sets of constellations. Today, the entire Celestial Sphere has been divided into 88 constellations, each of which is centered around a recognizable pattern of bright stars. The IAU (International Astronomical Union) divided the sky into these regions to help astronomers locate and identify astronomical objects. For example, the image below shows the constellation Sagittarius, with its assigned region of sky in white.
(More examples of animating parallax in video games.)
