Constellations Are Not Physical Groupings

The apparent groupings of stars into constellations that we see on the celestial sphere are not physical groupings. In most cases the stars in constellations are each at very different distances from us, and only appear to be grouped because they lie in approximately the same direction. This is illustrated in the following figure for the stars of the Big Dipper, where their physical distance from the Earth is drawn to scale (numbers beside each star give the distance from Earth in light years).

The Constellations of the Zodiac

The zodiac is an imaginary band 18 degrees wide and centered on the ecliptic. The constellations that fall in the zodiac are called the 12 constellations of the zodiac. They were at one time thought to have great mystical and astrological significance. Astrology is bunk, but the constellations of the zodiac are still of importance because the planets, as well as the Sun and Moon, are all near or on the ecliptic at any given time; thus, they are always found within one of the zodiac constellations.

Map of Winter Time Northern Constellations