Zodiac

The zodiac is a belt of sky along the apparent paths of the Sun, Moon, and planets, divided into signs or constellations. Its divisions underpin systems of celestial mapping and astrology.

Ecliptic: The apparent annual path of the Sun across the celestial sphere, near which the Moon and planets also appear. The zodiac is centered on this apparent path through the sky.
Sidereal zodiac: A twelve-sign zodiac aligned approximately with fixed stars and the constellations. It contrasts with the tropical zodiac’s alignment to equinoxes.
Babylonian astronomy: The systematic observation and recording of celestial phenomena in ancient Mesopotamia. Babylonian astronomers developed the zodiac’s twelve-sign framework.
Ecliptic longitude: An angular coordinate measured eastward along the ecliptic from a chosen reference point. Zodiac signs correspond to successive ranges of ecliptic longitude in the tropical system.
Celestial sphere: An imagined sphere surrounding Earth onto which celestial objects are projected for describing their positions. The zodiac is a mapped region on this model of the sky.
Zodiacal constellation: A constellation crossed by the ecliptic, including constellations beyond the twelve traditional zodiac signs. The Sun’s apparent path crosses these sky regions, whose widths are unequal.
Babylonian zodiac: An ancient Mesopotamian division of the ecliptic into twelve signs, developed in the first millennium BCE. It established the framework inherited by later zodiac systems.
Astrology: A set of traditions that interpret celestial positions as meaningful for human affairs or events. The zodiac supplies the signs used in many astrological systems.
Ecliptic coordinate system: A celestial coordinate system that uses the ecliptic as its fundamental plane. It locates objects using the same sky plane that defines the zodiac.
Equinox: Either of the two moments each year when the Sun crosses the celestial equator. The March equinox anchors the starting point of the tropical zodiac.

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