The band of stars seen from the earth as appearing within nine degrees on either side of the plane of Earth’s orbit around the sun.

The astronomers could note that within a zone about 18 degrees wide, extending 9 degrees on each side of the ecliptic, lie the apparent paths of the sun, moon, and major planets, as viewed from the earth. It was not until the second century B.C.E., however, that a Greek astronomer divided the zodiac into 12 equal parts of 30 degrees each; these parts came to be called the signs of the zodiac and were named after the related constellations. The word “zodiac” is from the Greek and means “circle of animals,” since most of the zodiac’s 12 constellations originally were designated by the names of animal or marine life.