Faith Woods, ape 13, of Phoenix, Arizona, for her question:
How did the zodiac signs get started?
The zodiac is a circle of 12 constellations that pace around the skies in step with the changing seasons. What we see of it depends on the earth's motions, in relation to the positions of the stars in outer space. Its usefulness as a calendar was discovered in prehistory. Thousands of years ago, early astronomers divided the 360 degrees celestial circle into the twelve 30 degrees sections, or signs of the zodiac.
What we see in a clear sky is a panorama of outer space. Our total view is the celestial sphere, which surrounds our entire globe like the inside of an enormous ball. However, we see only half of it at a time. This is the breathtaking celestial dome, like an inverted bowl resting on the horizon and towering to the zenith directly overhead. Our particular view depends on where and also when we happen to be on a particular spot of the earth's surface.
As the earth rotates, our view of the celestial dome changes moment by moment. Since we rotate towards the east, the heavenly bodies rise in the east and set out of sight in the west. Every 24 hours, the complete celestial sphere swings overhead, including the complete zodiac circle. But during the day, the stars up there are masked by the dazzling sun, including, half of the zodiac circle.
As we orbit the sun, the stars rise about four minutes earlier each evening, which gradually brings a changing series of constellations into view. Sprawling Scorpio and glowering Taurus are on opposite sides of the zodiac circle. In summer, when Scorpio dominates our night, Taurus rides over the sky with the dazzling daytime sun. During the year, the zodiac calendar gradually swings its 12 constellations from day to night in step with the changing seasons.
Its starry circle is level with the earth's orbit. But our axis is tilted 23 1/2 degrees to the orbital plane and we get a tilted view of the zodiac. It spans the sky in a sloping arch and its 12 constellations occupy a pathway about 36 times wider than the full moon. The major planets also travel within this highway and doom the center marches the dazzling daytime sun.
Zodiac means the circle of animals, perhaps because the ancients named its 12 constellations for sacred animal totems. Maybe Libra, Virgo and Gemini were renamed later. Sagittarius and Aquarius are reminders of long gone heroes. But we still have Leo, the celestial Lion, and Cancer, the heavenly Crab, Taurus the Bull and Aries the Ram, Pisces the Fishes, Capricorn the Goat and Scorpio the Scorpion.
The early Mesopotamians segmented the circle into 360 equal degrees, no doubt because they needed manageable circles to chart the heavens. Later the zodiac was divided into 12 sections, or signs of 30 degrees one for each of its constellations. Since then, the earth's axis has changed the direction of its pointing finger very slightly and the circle has inched slightly westward. The original sign of Taurus now is occupied by Aries and Taurus occupies the old sign of Gemini.