Some time during the 1st millennium B.C., Babylonian astronomers decided to split the ecliptic into twelve equal sections to create the first discovered celestial coordinate system. The zodiac also sometimes refers to a region of the celestial sphere that binds the paths of our Moon and Mercury, Venus, Mars, Jupiter, and Saturn (also known as the naked eye planets). The astronomers from long ago referred to these planets as the wandering stars to distinguish them from the stars that do not move.

Technically, the original classical zodiac signs should include those that are not represented by animals, such as Libra, Virgo, and Gemini. However, it can be argued that its correlation with animals derives from early perceptions of the constellations and the sculpted animals that were common. As for the Chinese zodiac, its core concept is to understand the movement of the planets and the Sun as a way to explain certain happenings one earth.

Like any prehistoric discovery, we cannot be completely sure how people responded to this astrological breakthrough. The geo-centrist view is that celestial objects move in relation to the Earth, hence the Earth is acting as a frame of reference. This means that they are rotating around the Earth as would other objects rotate around other planets and the moon, yet much slowly. Objectively speaking, then, the Earth would be the center of everything in the Universe. Likewise, stars also travel in respect to Earth and not the other way around. This specific view of geo-centrists is quite similar to that of the father of astrology, Ptolemy: “The sphere of the fixed stars also performs a motion of its own in the opposite direction to the revolution of the universe, that is [the motion of] the great circle through both poles, that of the equator and that of the ecliptic.” Ptolemy mentions the daily cycle as the rotation of the Earth, which is a result of the revolution of the universe. Nonetheless, it can be found that in Ptolemys The Almagest, he claims an alternative view, the fixed celestial sphere, or rather that he at least understands the difference between the two distinct motions. After endless construction of models of star constellations, Ptolemy finally concluded that since it is not reasonable to mark the solstitial and equinoctial points on the actual zodiac of the globe (for the stars depicted [on the globe] do not retain a constant distance with respect to these points), we need to take some fixed starting point in the delineated fixed stars." Thus Ptolemy‘s complicated resolution is that the zodiac travels through the equinox and the equinox through the zodiac.

Although the zodiac signs are still used today to serve as the pillar of the coordinate system, modern astronomers seem to prefer equatorial coordinate systems. These zodiacal signs, however, are actually modernized simplifications of the traditional pictorial representations from the Hellenistic times.

As you probably already know, astrologers often use their nighttime astronomical observations, s uch as star constellations and its relation to zodiac, for divinatory purposes. Modern astrology continues to utilize zodiac interpretation, but the debate of tropical versus sidereal coordinate systems also remains at large. The basic issue at hand is whether the symbols should be defined in terms of its position within the constellations that are the same or whether the symbols should be defined in terms of the various zones that are formed from Earth‘s motion during a tropical year. The existence of these two different astronomical coordinate systems suggests that the Sun travels through each zodiac symbol at distinct times of the year, resulting in multiple different mappings of the symbols to each day of the year.

Despite the existence of two distinct coordinate systems, modern astrologers map the position of the Sun and the planets in regards to the zodiac system. Then how does the horoscope come into play? The horoscope is used to compare and link characteristics of a specific sign with the characteristics of planets that are situated in that sign. These characteristics of planets are ideally supposed to influence the events on Earth but how it influences the Earth varies depending on how the sign is positioned.

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