Zodiac

The Zodiac: Definition, History, and the Twelve Signs

What Is the Zodiac?

The Zodiac is a band of the sky through which the Sun, Moon, and planets appear to travel. This celestial pathway extends approximately 8–9 degrees north and south of the Ecliptic, the apparent path of the Sun across the sky.

In both astronomy and astrology, the Zodiac is traditionally divided into 12 equal sections, known as Zodiac signs, each measuring 30 degrees of celestial longitude.

The First Point of Aries (Vernal Equinox)

The starting point of the Zodiac is defined as 0° longitude, known as the First Point of Aries. This point corresponds to the Vernal Equinox, when day and night are of equal length and the Sun crosses the celestial equator.

History of the Zodiac

The word “Zodiac” comes from the Latin Zodiacus, derived from the Greek meaning “Circle of Animals.” This name reflects the fact that more than half of the Zodiac signs are represented by animals.

The origins of the Zodiac date back to the Sumerian city-states of Mesopotamia, such as Ur, between 3800 BCE and 2700 BCE. These early systems of celestial observation were later adopted and refined by the ancient Greeks around 500 BCE, forming the foundation of Western astronomy and astrology.

Astronomical Definition of the Zodiac

• A circular band centered on the Ecliptic
• Extends approximately 8–9 degrees north and south of the Ecliptic
• Begins at the First Point of Aries (Vernal Equinox)
• Divided into 12 equal segments of 30 degrees each
• Each segment is named after a Constellation and referred to as a Zodiac sign

The Twelve Signs of the Zodiac

Sources

• Ptolemy, Ptolemy's Almagest.