Truly Zodiac

 In both astrology and historical astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude that are centered upon the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The paths of the Moon and visible planets also remain close to the ecliptic, within the belt of the zodiac, which extends 8-9° north or south of the ecliptic, as measured in celestial latitude. Because the divisions are regular, they do not correspond exactly to the twelve constellations after which they are named.
Historically, these twelve divisions are called signs. Essentially, the zodiac is a celestial coordinate system, or more specifically an ecliptic coordinate system, which takes the ecliptic as the origin of latitude, and the position of the Sun at vernal equinox as the origin of longitude.
Usage  
The zodiac was in use by the Roman era, based on concepts inherited by Hellenistic astronomy from Babylonian astronomy of the Chaldean period, which, in turn, derived from an earlier system of lists of stars along the ecliptic. The construction of the zodiac is described in Ptolemy's vast 2nd century AD work, the Almagest.
The term zodiac derives from Latin zōdiacus, which in its turn comes from the Greek, meaning "circle of animals", derived from, the diminutive of  "animal". The name is motivated by the fact that half of the signs of the classical Greek zodiac are represented as animals .
Although the zodiac remains the basis of the ecliptic coordinate system in use in astronomy besides the equatorial one, the term and the names of the twelve signs are today mostly associated with horoscopic astrology. The term "zodiac" may also refer to the region of the celestial sphere encompassing the paths of the planets corresponding to the band of about eight arc degrees above and below the ecliptic. The zodiac of a given planet is the band that contains the path of that particular body; e.g., the "zodiac of the Moon" is the band of five degrees above and below the ecliptic. By extension, the "zodiac of the comets" may refer to the band encompassing most short-period comets.
History  
Early history  
The division of the ecliptic into the zodiacal signs originates in Babylonian  astronomy during the first half of the 1st millennium BC, likely during Median/"Neo-Babylonian" times .
The classical zodiac is a modification of the MUL.APIN catalogue, which was compiled around 1000 BC.
Some of the constellations can be traced even further back, to Bronze Age  sources, including Gemini "The Twins", from MAŠ.TAB.BA.GAL.GAL "The Great Twins", and Cancer "The Crab", from AL.LUL "The Crayfish", among others.
Babylonian astronomers at some stage during the early 1st millennium BC divided the ecliptic into twelve equal zones of celestial longitude to create the first known celestial coordinate system: a coordinate system that boasts some advantages over modern systems . The Babylonian calendar as it stood in the 7th century BC assigned each month to a sign, beginning with the position of the Sun at vernal equinox, which, at the time, was depicted as the Aries constellation, for which reason the first sign is still called "Aries" even after the vernal equinox has moved away from the Aries constellation due to the slow precession of the Earth's axis of rotation.
Because the division was made into equal arcs, 30° each, they constituted an ideal system of reference for making predictions about a planet's longitude. However, Babylonian techniques of observational measurements were in a rudimentary stage of evolution and it is unclear whether they had techniques to define in a precise way the boundary lines between the zodiacal signs in the sky. Thus, the need to use stars close to the ecliptic  as a set of observational reference points to help positioning a planet within this ecliptic coordinate system. Constellations were given the names of the signs and asterisms could be connected in a way that would resemble the sign's name. Therefore, in spite of its conceptual origin, the Babylonian zodiac became sidereal.
In Babylonian astronomical diaries, a planet position was generally given with respect to a zodiacal sign alone, less often in specific degrees within a sign. When the degrees of longitude were given, they were expressed with reference to the 30° of the zodiacal sign, i.e., not with a reference to the continuous 360° ecliptic. To the construction of their mathematical ephemerides, daily positions of a planet were not as important as the dates when the planet crossed from one zodiacal sign to the next.
Knowledge of the Babylonian zodiac is also reflected in the Hebrew Bible. E. W. Bullinger interpreted the creatures appearing in the books of Ezekiel and Revelation as the middle signs of the four quarters of the Zodiac, with the Lion as Leo, the Bull is Taurus, the Man representing Aquarius and the Eagle representing Scorpio. Some authors have linked the twelve tribes of Israel with the twelve signs. Martin and others have argued that the arrangement of the tribes around the Tabernacle  corresponded to the order of the Zodiac, with Judah, Reuben, Ephraim, and Dan representing the middle signs of Leo, Aquarius, Taurus, and Scorpio, respectively. Such connections were taken up by Thomas Mann, who in his novel Joseph and His Brothers attributes characteristics of a sign of the zodiac to each tribe in his rendition of the Blessing of Jacob.
Hellenistic and Roman era  
The Babylonian star catalogs entered Greek astronomy in the 4th century BC, via Eudoxus of Cnidus.
Babylonia or Chaldea in the Hellenistic world came to be so identified with astrology that "Chaldean wisdom" became among Greeks and Romans the synonym of divination through the planets and stars.
Hellenistic astrology derived in part from Babylonian and Egyptian astrology.
Horoscopic astrology first appeared in Ptolemaic Egypt. The Dendera zodiac, a relief dating to ca. 50 BC, is the first known depiction of the classical zodiac of twelve signs.
Particularly important in the development of Western horoscopic astrology was the astrologer and astronomer Ptolemy, whose work Tetrabiblos laid the basis of the Western astrological tradition. Under the Greeks, and Ptolemy in particular, the planets, Houses, and signs of the zodiac were rationalized and their function set down in a way that has changed little to the present day. Ptolemy lived in the 2nd century AD, three centuries after the discovery of the precession of the equinoxes by Hipparchus around 130 BC. Hipparchus's lost work on precession never circulated very widely until it was brought to prominence by Ptolemy, and there are few explanations of precession outside the work of Ptolemy until late Antiquity, by which time Ptolemy's influence was widely established. Ptolemy clearly explained the theoretical basis of the western zodiac as being a tropical coordinate system, by which the zodiac is aligned to the equinoxes and solstices, rather than the visible constellations that bear the same names as the zodiac signs.
Hindu zodiac  
The Hindu zodiac uses the sidereal coordinate system, which makes reference to the fixed stars. The Tropical zodiac  is divided by the intersections of the ecliptic and equator, which shifts in relation to the backdrop of fixed stars at a rate of 1° every 72 years, creating the phenomenon known as precession of the equinoxes. The Hindu zodiac, being sidereal, does not maintain this seasonal alignment, but there are still similarities between the two systems. The Hindu zodiac signs and corresponding Greek signs sound very different, being in Sanskrit and Greek respectively, but their symbols are nearly identical. For example, dhanu means "bow" and corresponds to Sagittarius, the "archer", and kumbha means "water-pitcher" and corresponds to Aquarius, the "water-carrier".
Middle Ages  
The High Middle Ages saw a revival of Greco-Roman magic, first in Kabbalism and later continued in Renaissance magic. This included magical uses of the zodiac, as found, e.g., in the Sefer Raziel HaMalakh.
The zodiac is found in mediaeval stained glass as at Angers Cathedral, where the master glassmaker, André Robin, made the ornate rosettes for the North and South transepts after the fire there in 1451.
Early modern  
An example of the use of signs as astronomical coordinates may be found in the Nautical Almanac and Astronomical Ephemeris for the year 1767. The "Longitude of the Sun" columns show the sign, degrees from 0 to 29, minutes, and seconds.
The zodiacal symbols are Early Modern simplifications of conventional pictorial representations of the signs, attested since Hellenistic times.
The twelve signs  
What follows is a list of the twelve signs of the modern zodiac, where 0° Aries is understood as the vernal equinox, with their Latin, Greek, Sanskrit, and Babylonian names . Also, the "English translation" is not usually used by English speakers. The Latin names are standard English usage.
Constellations  
The zodiacal signs are distinct from the constellations associated with them, not only because of their drifting apart due to the precession of equinoxes but also because the physical constellations take up varying widths of the ecliptic, so the Sun is not in each constellation for the same amount of time. Thus, Virgo takes up five times as much ecliptic longitude as Scorpius. The zodiacal signs are an abstraction from the physical constellations, and each represent exactly one twelfth of the full circle, or the longitude traversed by the Sun in about 30.4 days.
Some "parazodiacal" constellations are also touched by the paths of the planets. The MUL.APIN lists Orion, Perseus, Auriga, and Andromeda. Furthermore, there are a number of constellations mythologically associated with the zodiacal ones : Piscis Austrinus, The Southern Fish, is attached to Aquarius. In classical maps, it swallows the stream poured out of Aquarius' pitcher, but perhaps it formerly just swam in it. Aquila, The Eagle, was possibly associated with the zodiac by virtue of its main star, Altair. Hydra in the Early Bronze Age marked the celestial equator and was associated with Leo, which is shown standing on the serpent on the Dendera zodiac. Corvus is the Crow or Raven mysteriously perched on the tail of Hydra.
Due to the constellation boundaries being redefined in 1930 by the International Astronomical Union, the path of the ecliptic now officially passes through thirteen constellations: the twelve traditional 'zodiac constellations' plus Ophiuchus, the bottom part of which interjects between Scorpio and Sagittarius. Ophiuchus is an anciently recognized constellation, catalogued along with many others in Ptolemy's Almagest, but not historically referred to as a zodiac constellation. The inaccurate description of Ophiuchus as a sign of the zodiac drew media attention in 1995, when the BBC Nine O'Clock News reported that "an extra sign of the zodiac has been announced by the Royal Astronomical Society". There had been no such announcement, and the report had merely sensationalized the 67-year-old 'news' of the IAU's decision to alter the number of designated ecliptic constellations.
Table of dates  
The following table compares the Gregorian dates on which the Sun enters
a sign in the Ptolemaic tropical zodiac
a sign in the Hindu sidereal system
the astronomical constellation of the same name as the sign, with constellation boundaries as defined in 1930 by the International Astronomical Union.
The theoretical beginning of Aries is the moment of vernal equinox, and all other dates shift accordingly.
The precise Gregorian times and dates vary slightly from year to year as the Gregorian calendar shifts relative to the tropical year. These variations remain within less than two days' difference in the recent past and the near-future, vernal equinox in UT always falling either on 20 or 21 March in the period of 1797 to 2043, falling on 19 March in 1796 the last time and in 2044 the next.
{  class "wikitable" style "text-align:left"
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! colspan "4"   Sign
! colspan "4"   Constellation
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! Name
! Symbol
! Tropical zodiac
! Sidereal zodiac
! Name
! IAU boundaries
! Solar stay
Precession of the equinoxes  
The zodiac system was developed in Babylonia, some 2,500 years ago, during the "Age of Aries". At the time, it is assumed, the precession of the equinoxes was unknown, as the system made no allowance for it. Contemporary use of the coordinate system is presented with the choice of interpreting the system either as sidereal, with the signs fixed to the stellar background, or as tropical, with the signs fixed to the point of vernal equinox.
Western astrology takes the tropical approach, whereas Hindu astrology takes the sidereal one. This results in the originally unified zodiacal coordinate system drifting apart gradually, with a clockwise precession of 1.4 degrees per century.
For the tropical zodiac used in Western astronomy and astrology, this means that the tropical sign of Aries currently lies somewhere within the constellation Pisces .
The sidereal coordinate system takes into account the ayanamsa, ayan meaning transit or movement, and amsa meaning small part, i.e. movement of equinoxes in small parts. It is unclear when Indians became aware of the precession of the equinoxes, but Bhaskar II's 12th-century treatise Siddhanta Shiromani gives equations for measurement of precession of equinoxes, and says his equations are based on some lost equations of Suryasiddhanta plus the equation of Munjaala.