Origins of the Zodiac

The Sumerian civilization (Mesopotamia) developed mathematics using a counting system that was based on the number 60, from which was born the concept of 360degrees for a circle (60 x 60) and the actual time system. 
They also divided the day (mean circumference) in "12 Steps" solar, which would later become the 12-hour and 12 hours of the night.

They believed that the stars were fixed to the sphere located beyond Saturn, hence so-called "fixed stars" to the stars and "shooting stars" to the planets. They were the first to define the 12 constellations of the zodiac, who traveled in 12 periods which together formed a solar year. Hence, the year was divided into 12 months and four seasons of three months each.
However, the priest-astronomers or astrologers of ancient Egypt were the ones who passed this knowledge and their own observations of the sky to the Greeks, who in turn were a source of knowledge for astronomers and scientists from the Middle Ages.

Astronomy Zodiac: The relation between astronomy and zodiac signs

The word “zodiac” comes from the Greek zodiacs (circle of animals) and with it the sky was divided into twelve parts including each of the zodiacal signs and other constellations, which were assigned mainly mythological names. The ecliptic, or apparent movement that makes the sun around the Earth, is conventionally divided into twelve sections which are located the 12 constellations that make up the zodiac, so that each month the sun through one of the signs of the Zodiac, precisely that which we can not see at night.

Since the subdivisions of the zodiac received their names, the precession of the equinoxes (rolling movement around the axis of rotation) shifted the zodiacal band of the sky as it is seen from the Earth, but the old names have not been modified, thus these names have not relation at all with the original constellation.

Astrological Zodiac

The Astrological Zodiac is Chaldean legacy, a people who lived three thousand years ago in Mesopotamia (now Iraq) who believed in the stars was the will of the gods. They divided the sky into twelve equal parts (30 degrees each) and gave the constellation name as observed here and today we know as Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius and Pisces. However, the word Zodiac is of Greek origin and means (in ancient Greek) something like "animal environment," referring to the Chaldean beliefs.

Today, the position of the constellations does not "fit" with the zodiacal signs (Chaldeans) of the same name. By comparing a map of the stars made ​​by the Greeks in antiquity with a current map, we see that the focus of rotation of the Earth (precession equinoctial) has moved about ten (or more) degrees. The North Star at that time was not right on the North Pole as today, and, Ecuador, during the time it has moved about thirty degrees.

Should be noted that the Greeks had knowledge about it because, the "equinoctial precession" was discovered by Claudius Ptolemy comparing their measurements of the position of the stars with which Hipparchus had done two centuries earlier. Newton discovered that the axis of rotation of the Earth is not fixed because the Earth is not completely spherical because the gravitational forces exercised by the moon and sun acting on the Earth's equatorial bulge.

                       
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                                     The constellations

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