Using such symbols worked so well that the Babylonians also assigned a symbol to each planet. When creating maps of the sky, the Babylonians drew the symbols of each zodiac constellation around the outside of the circle and put the symbols for each planet on the perimeter of the circle to show where the positions of the planets were. Figure 3D is an example of how the Babylonians used the circle to draw a map of the sky around the time they first did so, over 4,000 years ago. The illustration represents maps of the sky with the Earth at the center of the circle, the planets at the perimeter of the circle, and the 12 zodiac signs on the outside of the circle, which were used originally as guideposts. The 12 constellation (signs) are each 30 degrees. The degrees for the planets are always numbered from 0 through 29 and never higher than 30, because once a planet moves beyond the 30th degree of any zodiac constellation, it is within the borders of a new zodiac constellation. Such illustrations were meant to be maps of the sky, and they were the first astrology charts that resembled modern-day birth charts.

The Babylonians learned very early that the alignment of the planets on the day a person is born is very important. These circular charts were really the first BIRTH CHARTS, or NATAL CHARTS. The term natal means "birth" and is derived from the same Latin word as that which gave rise to another word about birth, nativity. The term NATAL PLANETS refers to the positions of the planets that someone was born with.

The Babylonian Astrologers Invent the Circle ...
Because the changes in the positions of the planets were possible celestial signs and therefore very important to the Babylonians, they needed a way to keep track of the planets' movements. This was not as easy to do as you might think. Many civilizations tried to devise a reliable way of keeping track of the movements of the planets but did not succeed in doing so. The Babylonian astrologers were the first to accomplish this.

To do it, they invented the circle. Have you ever wondered why a circle has 360 degrees instead of 50 degrees or 100 degrees? A circle has 360 degrees because the circle was designed by Babylonian astrologers to be a map of the sky. And there are 360 degrees in a circle because the Sun moves almost exactly one degree a day. The Sun actually moves about 0.9856 degrees per day, but one degree a day was close enough for the Babylonians 4,000
years ago. Figure 3B is an example of how the Babylonians used the
circle as a map to help them both record and illustrate the positions of the planets in the sky. The way they did this was both simple and ingenious. Since the planets moved around and around in the sky, they placed the Earth at the center of the circle and drew the positions of the planets on the circumference of the circle. They began to do this more than 4,000 years ago.

The Babylonian astrologers invented and used their circle with its 360 degrees to help them record and illustrate the positions of the Sun, Moon, and the planets every single night for thousands of years as they looked for celestial signs in the sky of impending mega-events. For thousands of years!

The Stars Were Grouped into Constellations ...
Sometime early on during those thousands of years, the Babylonians figured out that they needed reference points so that they could easily locate the planets in the nighttime sky. After all, it could be very difficult to find a planet other than the Sun and Moon. For this reason, the Babylonians divided the sky into constellations. This way, they had clear guideposts for the positions of the planets. For example, if you wanted to find Jupiter, they might say, "Tonight Jupiter is just a little east of the brightest star in the
Taurus constellation."

Originally, the Babylonians believed that they needed reference points over the entire visible sky in order to track the movements of the seven visible planets. So they grouped the visible stars into about 48 different constellations. Then after several hundreds of years of observation, they began to realize that the planets' movements were always limited to a narrow circular band of the sky that was only about 50 degrees
wide. The planets did not ever go above or below this 50-degree-wide band. The planets didn't do it then, and they still don't do it now. This 50-degree-wide band in the sky that delineates the boundaries of the movement of the planets is now called the ECLIPTIC. The ecliptic is sort of like the equator, but it is wider, and is in the sky rather than around the Earth. It is most easily defined as the path of the Sun across the sky measured against the stars that are fixed. (Please see Figure 3C) All the planets travel across the sky in such a way that they are normally positioned within this approximately 50-degree-band in the sky.
In these modern times, we know that there are nine planets plus the Sun and Moon.

But the Babylonians could only see five of the planets plus the Sun and Moon. These five planets were Mercury, Venus, Mars, Jupiter, and Saturn. Together with the Sun and Moon, we refer to them as the SEVEN VISIBLE PLANETS. Because the seven visible planets rarely moved above or below the ecliptic, the most important constellations became the ones that were within the boundaries of the ecliptic. The ecliptic also became known commonly as the zodiac, and the constellations that were within the zodiac became known as the zodiac constellations. The Babylonians had 12 of them.

They were the ones that covered the path of travel of the planets. Naturally, since the Babylonians were looking for celestial signs, somewhere along the way, these 12 zodiac constellations were also called the 12 Zodiac signs.

The 12 zodiac constellations were named Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. Legends grew up about them and their origins-legends that became a part of what we now call mythology.

The most important thing to bear in mind about the constellations is that they were initially devised by the Babylonians as guideposts to help them find the planets. Therefore, the Babylonians needed to include the zodiac constellations in their circular maps of the sky. In order to facilitate the drawing of their circles as maps of the sky, the
Babylonians assigned a unique symbol to represent each zodiac constellation; in this way, they could just put the symbol of the zodiac sign on the circle rather than drawing a whole lot of stars. Many of you are probably familiar with the symbols for the 12 zodiac constellations. For example, here are the symbols for the Taurus and Gemini
constellations: