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86-597: The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south (as measured in celestial latitude ) of the ecliptic , the apparent path of the Sun across the celestial sphere over the course of the year. Also within this zodiac belt appear the Moon and the brightest planets , along their orbital planes. The zodiac is divided along the ecliptic into 12 equal parts ("signs") , each occupying 30° of celestial longitude . These signs roughly correspond to
172-412: A celestial sphere , if the object's distance is unknown or trivial. Spherical coordinates , projected on the celestial sphere, are analogous to the geographic coordinate system used on the surface of Earth . These differ in their choice of fundamental plane , which divides the celestial sphere into two equal hemispheres along a great circle . Rectangular coordinates , in appropriate units , have
258-548: A right-handed convention. The origin at the centre of Earth means the coordinates are geocentric , that is, as seen from the centre of Earth as if it were transparent . The fundamental plane and the primary direction mean that the coordinate system, while aligned with Earth's equator and pole , does not rotate with the Earth, but remains relatively fixed against the background stars . A right-handed convention means that coordinates increase northward from and eastward around
344-437: A left-handed system, measures the angular distance of an object westward along the celestial equator from the observer's meridian to the hour circle passing through the object. Unlike right ascension, hour angle is always increasing with the rotation of Earth . Hour angle may be considered a means of measuring the time since upper culmination , the moment when an object contacts the meridian overhead. A culminating star on
430-407: A measurement of the position of a planet or spacecraft is made. There are also subdivisions into "mean of date" coordinates, which average out or ignore nutation , and "true of date," which include nutation. The fundamental plane is the plane of the Earth's orbit, called the ecliptic plane. There are two principal variants of the ecliptic coordinate system: geocentric ecliptic coordinates centered on
516-627: A planet were not as important as the astrologically significant dates when the planet crossed from one zodiacal sign to the next. Knowledge of the Babylonian zodiac is said to be reflected in the Hebrew Bible ; E. W. Bullinger interpreted the creatures that appear in the book of Ezekiel ( 1:10 ) as the middle signs of the four quarters of the zodiac, with the Lion as Leo , the Bull as Taurus ,
602-514: A result of the method of measuring right ascensions by timing the passage of objects across the meridian as the Earth rotates . There are 360° / 24 = 15° in one hour of right ascension, and 24 of right ascension around the entire celestial equator . When used together, right ascension and declination are usually abbreviated RA/Dec. Alternatively to right ascension , hour angle (abbreviated HA or LHA, local hour angle ),
688-442: A rudimentary stage of evolution. They measured the position of a planet in reference to a set of "normal stars" close to the ecliptic (±9° of latitude). The normal stars were used as observational reference points to help position a planet within this ecliptic coordinate system. In Babylonian astronomical diaries , a planet position was generally given with respect to a zodiacal sign alone, though less often in specific degrees within
774-405: 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. In astronomical ephemerides , the positions of significant astronomical phenomena were computed in sexagesimal fractions of a degree (equivalent to minutes and seconds of arc ). For daily ephemerides, the daily positions of
860-442: A small oscillation of the Earth's axis, nutation . In order to fix the exact primary direction, these motions necessitate the specification of the equinox of a particular date, known as an epoch , when giving a position. The three most commonly used are: A position in the equatorial coordinate system is thus typically specified true equinox and equator of date , mean equinox and equator of J2000.0 , or similar. Note that there
946-411: A star's position differs from observer to observer based on their positions on the Earth's surface, and is continuously changing with the Earth's rotation. Telescopes equipped with equatorial mounts and setting circles employ the equatorial coordinate system to find objects. Setting circles in conjunction with a star chart or ephemeris allow the telescope to be easily pointed at known objects on
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#17327727758811032-416: A takht. First, the astrologer would use an astrolabe to find the position of the sun, align the rule with the persons time of birth and then align the rete to establish the altitude of the sun on that date. Next, the astrologer would use an Ephemeris, a table denoting the mean position of the planets and stars within the sky at any given time. Finally, the astrologer would add the altitude of the sun taken from
1118-658: A very few years of 401 BC. Unlike modern astrologers, who place the beginning of the sign of Aries at the position of the Sun at the vernal equinox in the Northern Hemisphere ( March equinox ), Babylonian astronomers fixed the zodiac in relation to stars, placing the beginning of Cancer at the "Rear Twin Star" ( β Geminorum ) and the beginning of Aquarius at the "Rear Star of the Goat-Fish" ( δ Capricorni ). Due to
1204-459: Is a celestial coordinate system widely used to specify the positions of celestial objects . It may be implemented in spherical or rectangular coordinates, both defined by an origin at the centre of Earth , a fundamental plane consisting of the projection of Earth's equator onto the celestial sphere (forming the celestial equator ), a primary direction towards the March equinox , and
1290-524: Is analogous to terrestrial latitude . The right ascension symbol α , (lower case "alpha", abbreviated RA) measures the angular distance of an object eastward along the celestial equator from the March equinox to the hour circle passing through the object. The March equinox point is one of the two points where the ecliptic intersects the celestial equator. Right ascension is usually measured in sidereal hours, minutes and seconds instead of degrees,
1376-497: Is associated with different attributes. The zodiacal system and its angular measurement in 360 sexagesimal degree (°) originated with Babylonian astronomy during the 1st millennium BC . It was communicated into Greek astronomy by the 2nd century BC, as well as into developing the Hindu zodiac . Due to the precession of the equinoxes , the time of year that the Sun is in a given constellation has changed since Babylonian times, and
1462-475: Is based on the position of the observer on Earth, which revolves around its own axis once per sidereal day (23 hours, 56 minutes and 4.091 seconds) in relation to the star background. The positioning of a celestial object by the horizontal system varies with time, but is a useful coordinate system for locating and tracking objects for observers on Earth. It is based on the position of stars relative to an observer's ideal horizon. The equatorial coordinate system
1548-570: Is centered at Earth's center, but fixed relative to the celestial poles and the March equinox . The coordinates are based on the location of stars relative to Earth's equator if it were projected out to an infinite distance. The equatorial describes the sky as seen from the Solar System , and modern star maps almost exclusively use equatorial coordinates. The equatorial system is the normal coordinate system for most professional and many amateur astronomers having an equatorial mount that follows
1634-408: Is given beneath each case. This division is ambiguous because tan has a period of 180° ( π ) whereas cos and sin have periods of 360° (2 π ). Azimuth ( A ) is measured from the south point, turning positive to the west. Zenith distance, the angular distance along the great circle from the zenith to a celestial object, is simply the complementary angle of the altitude: 90° − a . In solving
1720-433: Is no "mean ecliptic", as the ecliptic is not subject to small periodic oscillations. A star 's spherical coordinates are often expressed as a pair, right ascension and declination , without a distance coordinate. The direction of sufficiently distant objects is the same for all observers, and it is convenient to specify this direction with the same coordinates for all. In contrast, in the horizontal coordinate system ,
1806-417: Is not usually used by English speakers. The Latin names are standard English usage (except that "Capricorn" is used rather than "Capricornus"). These twelve signs have been arranged into a nursery rhyme as a mnemonic device: The ram, the bull, the heavenly twins, And next the crab, the lion shines, The virgin and the scales, The scorpion, archer, and the goat, The man who holds
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#17327727758811892-473: Is still the center of the coordinate system, and the zero point is defined as the direction towards the Galactic Center . Galactic latitude resembles the elevation above the galactic plane and galactic longitude determines direction relative to the center of the galaxy. The supergalactic coordinate system corresponds to a fundamental plane that contains a higher than average number of local galaxies in
1978-471: Is the first known depiction of the classical zodiac of twelve signs. The earliest extant Greek text using the Babylonian division of the zodiac into 12 signs of 30 equal degrees each is the Anaphoricus of Hypsicles of Alexandria (fl. 190 BC). Particularly important in the development of Western horoscopic astrology was the astrologer and astronomer Ptolemy , whose work Tetrabiblos laid
2064-670: The Chaldean period (mid-1st millennium BC), 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 comprehensive 2nd century AD work, the Almagest . 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
2150-572: 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. The vernal equinox has fallen on 20 March UT since 2008, and will continue to do so until 2043. As each sign takes up exactly 30 degrees of
2236-610: The Latinized form of the Ancient Greek zōdiakòs kýklos ( ζῳδιακός κύκλος ), meaning "cycle or circle of little animals". Zōdion ( ζῴδιον ) is the diminutive of zōon ( ζῷον , "animal"). The name reflects the prominence of animals (and mythological hybrids ) among the twelve signs. The zodiac was in use by the Roman era , based on concepts inherited by Hellenistic astronomy from Babylonian astronomy of
2322-417: The astronomical constellations with the following modern names: Aries , Taurus , Gemini , Cancer , Leo , Virgo , Libra , Scorpio , Sagittarius , Capricorn , Aquarius , and Pisces . The signs have been used to determine the time of the year by identifying each sign with the days of the year the Sun is in the respective sign. In Western astrology , and formerly astronomy , the time of each sign
2408-592: 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,
2494-415: The equator in the geographic coordinate system . The poles are located at ±90° from the fundamental plane. The primary direction is the starting point of the longitudinal coordinates. The origin is the zero distance point, the "center of the celestial sphere", although the definition of celestial sphere is ambiguous about the definition of its center point. The horizontal , or altitude-azimuth , system
2580-420: The precession of the equinoxes , the time of year the Sun is in a given constellation has changed since Babylonian times, as the point of March equinox has moved from Aries into Pisces . Because the divisions were made into equal arcs of 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
2666-419: The tan( A ) equation for A , in order to avoid the ambiguity of the arctangent , use of the two-argument arctangent , denoted arctan( x , y ) , is recommended. The two-argument arctangent computes the arctangent of y / x , and accounts for the quadrant in which it is being computed. Thus, consistent with the convention of azimuth being measured from the south and opening positive to
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2752-491: The "archer", and kumbha means "water-pitcher" and corresponds to Aquarius, the "water-carrier". During the Abbasid era , Greek reference books were translated into Arabic , and Islamic astronomers then did their own observations, correcting Ptolemy's Almagest. One such book was Al-Sufi 's Book of Fixed Stars , which has pictorial depictions of 48 constellations. The book was divided into three sections: constellations of
2838-488: The 14th century BC a complete list of the 36 Egyptian decans was placed among the hieroglyphs adorning the tomb of Seti I ; they figured again in the temple of Ramesses II , and characterize every Egyptian astrological monument. Both the famous zodiacs of Dendera display their symbols, identified by Karl Richard Lepsius . The division of the ecliptic into the zodiacal signs originates in Babylonian astronomy during
2924-416: The 1st century BC astronomical text of Geminus of Rhodes. Geminus explains that Greek astronomers of his era associate the first degrees of the zodiac signs with the two solstices and the two equinoxes, in contrast to the older Chaldean (Babylonian) system, which placed these points within the zodiac signs. This illustrates that Ptolemy merely clarified the convention of Greek astronomers and did not originate
3010-407: The Earth (in contrast to Earth-centred, Earth-fixed frames), remaining always directed toward the equinox , and drifting over time with the motions of precession and nutation . In astronomy, there is also a heliocentric rectangular variant of equatorial coordinates, designated x , y , z , which has: This frame is similar to the ξ , η , ζ frame above, except that the origin
3096-468: The Earth and heliocentric ecliptic coordinates centered on the center of mass of the Solar System. The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon, and planets. It was used to define the twelve astrological signs of the zodiac , for instance. The heliocentric ecliptic system describes
3182-592: The Earth's axis of rotation, rather than the plane of the planet's orbit around the Sun. Celestial latitude In astronomy , coordinate systems are used for specifying positions of celestial objects ( satellites , planets , stars , galaxies , etc.) relative to a given reference frame , based on physical reference points available to a situated observer (e.g. the true horizon and north to an observer on Earth's surface). Coordinate systems in astronomy can specify an object's relative position in three-dimensional space or plot merely by its direction on
3268-526: 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 (305 BC–30 BC). The Dendera zodiac , a relief dating to c. 50 BC ,
3354-673: The Man as Aquarius and the Eagle as a higher aspect of Scorpio. Some authors have linked the signs of the zodiac with the twelve tribes of Israel , and with the lunar Hebrew calendar , which has twelve lunar months in a lunar year . Martin and others have argued that the arrangement of the tribes around the Tabernacle (reported in the Book of Numbers ) corresponded to the order of the zodiac, with Judah , Reuben , Ephraim , and Dan representing
3440-435: The Sun is not in each constellation for the same amount of time. Thus, Virgo takes up 5 times as much ecliptic longitude as Scorpius . The zodiacal signs are an abstraction from the physical constellations, and each represent exactly 1 ⁄ 12 th of the full circle, but the time spent by the Sun in each sign varies slightly due to the eccentricity of the Earth's orbit . Sidereal astrology remedies this by assigning
3526-490: The Sun's planets have orbits that have only a slight inclination to the orbital plane of the Earth. Stars within the zodiac are subject to occultations by the Moon and other solar system bodies. These events can be useful, for example, to estimate the cross-sectional dimensions of a minor planet , or check a star for a close companion. The Sun's placement upon the vernal equinox, which occurs annually around 21 March, defines
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3612-491: The astrolabe, with the mean position of the planets on the person's birthday, and add them together on the takht (also known as the dustboard). The dust board was merely a tablet covered in sand; on which the calculations could be made and erased easily. Once this had been calculated, the astrologer was then able to interpret the horoscope. Most of these interpretations were based on the zodiac in literature. For example, there were several manuals on how to interpret each zodiac sign,
3698-561: 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' lost work on precession never circulated very widely until it
3784-507: The best date for founding the new capital of Baghdad. Whilst horoscopes were generally widely accepted by society, many scholars condemned the use of astrology and divination, linking it to occult influences. Many theologians and scholars thought that it went against the tenets of Islam; as only God should be able to determine events rather than astrologers looking at the positions of the planets. In order to calculate someone's horoscope, an astrologer would use 3 tools: an astrolabe, ephemeris and
3870-678: The bottom part of which interjects between Scorpio and Sagittarius. Occasionally this difference between the astronomical constellations and the astrological signs is mistakenly reported in the popular press as a "change" to the list of traditional signs by some astronomical body like the IAU, NASA , or the Royal Astronomical Society . This happened in a 1995 report of the BBC Nine O'Clock News and various reports in 2011 and 2016. Some "parazodiacal" constellations are touched by
3956-425: The celestial sphere. The declination symbol δ , (lower case "delta", abbreviated DEC) measures the angular distance of an object perpendicular to the celestial equator, positive to the north, negative to the south. For example, the north celestial pole has a declination of +90°. The origin for declination is the celestial equator, which is the projection of the Earth's equator onto the celestial sphere. Declination
4042-415: The end of the constellation Pisces, having been within that constellation since the 2nd century AD. The subsequent 30° of the ecliptic is nominally designated the zodiac sign Taurus, and so on through the twelve signs of the zodiac so that each occupies 1 ⁄ 12 th (30°) of the zodiac's great circle. Zodiac signs have never been used to determine the boundaries of astronomical constellations that lie in
4128-404: The end of the fifth century BC, Babylonian astronomers divided the ecliptic into 12 equal "signs", by analogy to 12 schematic months of 30 days each. Each sign contained 30° of celestial longitude , thus creating the first known celestial coordinate system. According to calculations by modern astrophysics, the zodiac was introduced between 409 and 398 BC, during Persian rule , and probably within
4214-549: The equation of Munjaala. The discovery of precession is attributed to Hipparchus around 130 BC. Ptolemy quotes from Hipparchus' now-lost work entitled "On the Displacement of the Solstitial and Equinoctial Points" in the seventh book of his 2nd century astronomical text, Almagest , where he describes the phenomenon of precession and estimates its value. Ptolemy clarified that the convention of Greek mathematical astronomy
4300-745: The equatorial coordinates of the North Galactic Pole and l NCP {\displaystyle l_{\text{NCP}}} is the Galactic longitude of the North Celestial Pole. Referred to J2000.0 the values of these quantities are: If the equatorial coordinates are referred to another equinox , they must be precessed to their place at J2000.0 before applying these formulae. These equations convert to equatorial coordinates referred to B2000.0 . Equatorial coordinate system The equatorial coordinate system
4386-415: The farther away from the equator the observer is situated, the greater the difference. Thus, signs are spoken of as "long" or "short" ascension . In tropical astrology , 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 because the physical constellations take up varying widths of the ecliptic, so
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#17327727758814472-575: The first half of the 1st millennium BC . The zodiac draws on stars in earlier Babylonian star catalogues , such as the MUL.APIN catalogue, which was compiled around 1000 BC. Some constellations can be traced even further back, to Bronze Age ( Old Babylonian Empire ) sources, including Gemini "The Twins", from Sumerian : 𒀯𒈦𒋰𒁀𒃲𒃲 , romanized: MAŠ.TAB.BA.GAL.GAL "The Great Twins"; Cancer "The Crab", from Sumerian : 𒀯𒀠𒇻 , romanized: AL.LUL "The Crayfish", among others. Around
4558-401: The fundamental plane. This description of the orientation of the reference frame is somewhat simplified; the orientation is not quite fixed. A slow motion of Earth's axis, precession , causes a slow, continuous turning of the coordinate system westward about the poles of the ecliptic , completing one circuit in about 26,000 years. Superimposed on this is a smaller motion of the ecliptic, and
4644-590: The influence that the stars have on events on the earth was important in Islamic civilization. As a rule, it was believed that the signs of the zodiac and the planets control the destiny not only of people but also of nations, and that the zodiac has the ability to determine a person's physical characteristics as well as intelligence and personal traits. The practice of astrology at this time could be divided into 4 broader categories: Genethlialogy, Catarchic Astrology, Interrogational Astrology and General Astrology. However
4730-461: 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 . The Babylonian star catalogs entered Greek astronomy in the 4th century BC, via Eudoxus of Cnidus . Babylonia or Chaldea in
4816-497: The most common type of astrology was Genethlialogy, which examined all aspects of a person's life in relation to the planetary positions at their birth; more commonly known as our horoscope. Astrology services were offered widely across the empire, mainly in bazaars, where people could pay for a reading. Astrology was valued in the royal courts, for example, the Abbasid Caliph Al-Mansur used astrology to determine
4902-421: The movement of the sky during the night. Celestial objects are found by adjusting the telescope's or other instrument's scales so that they match the equatorial coordinates of the selected object to observe. Popular choices of pole and equator are the older B1950 and the modern J2000 systems, but a pole and equator "of date" can also be used, meaning one appropriate to the date under consideration, such as when
4988-406: The natures of the signs from the theory of prognostication, or impossible to avoid error in then retaining and making use of them; as the regularity of their spaces and distances, upon which their influence depends, would then be invaded and broken in upon. Astronomically, the zodiac defines a belt of space extending 8° or 9° in celestial latitude to the north and south of the ecliptic , within which
5074-469: The observer's meridian is said to have a zero hour angle (0 ). One sidereal hour (approximately 0.9973 solar hours ) later, Earth's rotation will carry the star to the west of the meridian, and its hour angle will be 1 . When calculating topocentric phenomena, right ascension may be converted into hour angle as an intermediate step. There are a number of rectangular variants of equatorial coordinates. All have: The reference frames do not rotate with
5160-422: The orbits of the Moon and the principal planets remain. It is a feature of the ecliptic coordinate system – a celestial coordinate system centered upon the ecliptic (the plane of the Earth's orbit and the Sun's apparent path), by which celestial longitude is measured in degrees east of the vernal equinox (the ascending intersection of the ecliptic and equator). The zodiac is narrow in angular terms because most of
5246-475: The paths of the planets, leading to counts of up to 25 "constellations of the zodiac". The ancient Babylonian MUL.APIN catalog lists Orion , Perseus , Auriga , and Andromeda . Modern astronomers have noted that planets pass through Crater , Sextans , Cetus , Pegasus , Corvus , Hydra , Orion , and Scutum , with Venus very rarely passing through Aquila , Canis Minor , Auriga , and Serpens . Some other constellations are mythologically associated with
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#17327727758815332-530: The planets' orbital movement around the Sun, and centers on the barycenter of the Solar System (i.e. very close to the center of the Sun). The system is primarily used for computing the positions of planets and other Solar System bodies, as well as defining their orbital elements . The galactic coordinate system uses the approximate plane of the Milky Way Galaxy as its fundamental plane. The Solar System
5418-457: The point of March equinox has moved from Aries into Pisces . The zodiac forms a celestial coordinate system , or more specifically an ecliptic coordinate system , which takes the ecliptic as the origin of latitude and the Sun's position at vernal equinox as the origin of longitude. In modern astronomy, the ecliptic coordinate system is still used for tracking Solar System objects. The English word zodiac derives from zōdiacus ,
5504-468: The principle of the tropical zodiac, as is sometimes assumed. Ptolemy demonstrates that the principle of the tropical zodiac was well known to his predecessors within his astrological text, the Tetrabiblos , where he explains why it would be an error to associate the regularly spaced signs of the seasonally aligned zodiac with the irregular boundaries of the visible constellations: The beginnings of
5590-439: The region of the celestial sphere encompassing the paths of the planets corresponding to the band of about 8 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 5° above and below the ecliptic. By extension, the "zodiac of the comets" may refer to the band encompassing most short-period comets . As early as
5676-426: The same fundamental ( x, y ) plane and primary ( x -axis) direction , such as an axis of rotation . Each coordinate system is named after its choice of fundamental plane. The following table lists the common coordinate systems in use by the astronomical community. The fundamental plane divides the celestial sphere into two equal hemispheres and defines the baseline for the latitudinal coordinates, similar to
5762-554: The same names as the zodiac signs. According to mathematician-historian Montucla , the Hindu zodiac was adopted from the Greek zodiac through communications between ancient India and the Greek empire of Bactria . The Hindu zodiac uses the sidereal coordinate system , which makes reference to the fixed stars. The tropical zodiac (of Mesopotamian origin) is divided by the intersections of
5848-513: The serpent on the Dendera zodiac . 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. 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
5934-472: The signs fixed to the point ( vector of the Sun) at the March 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 (westward) precession of 1.4 degrees per century. For the tropical zodiac used in Western astronomy and astrology, this means that
6020-454: The signs, and likewise those of the terms, are to be taken from the equinoctial and tropical points. This rule is not only clearly stated by writers on the subject, but is especially evident by the demonstration constantly afforded, that their natures, influences and familiarities have no other origin than from the tropics and equinoxes, as has been already plainly shown. And, if other beginnings were allowed, it would either be necessary to exclude
6106-408: The sky as seen from Earth. Conversions between the various coordinate systems are given. See the notes before using these equations. The classical equations, derived from spherical trigonometry , for the longitudinal coordinate are presented to the right of a bracket; dividing the first equation by the second gives the convenient tangent equation seen on the left. The rotation matrix equivalent
6192-405: The starting point for measurement, the first degree of which is historically known as the " first point of Aries ". The first 30° along the ecliptic is nominally designated as the zodiac sign Aries, which no longer falls within the proximity of the constellation Aries since the effect of precession is to move the vernal point through the backdrop of visible constellations. It is currently located near
6278-548: The treatise relating to each individual sign and what the characteristics of these zodiacs were. 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 (represented as a digit from 0 to and including 11), degrees from 0 to 29, minutes, and seconds. Mughal king Jahangir issued an attractive series of coins in gold and silver depicting
6364-577: The tropical sign of Aries currently lies somewhere within the constellation Pisces (" Age of 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 Bhāskara 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
6450-401: The twelve signs of the zodiac. What follows is a list of the signs of the modern zodiac (with the ecliptic longitudes of their first points), where 0° Aries is understood as the vernal equinox, with their Latin, Greek, Sanskrit, and Babylonian names. But the Sanskrit and the name equivalents (after c.500 BC) denote the constellations only, not the tropical zodiac signs. The "English translation"
6536-459: The vicinity of the zodiac, which are, and always have been, irregular in their size and shape. The convention of measuring celestial longitude within individual signs was still being used in the mid-19th century, but modern astronomy now numbers degrees of celestial longitude continuously from 0° to 360°, rather than 0° to 30° within each sign. This coordinate system is primary used by astronomers for observations of solar system objects. The use of
6622-499: The watering-pot, And fish with glittering scales. The following table compares the Gregorian dates on which the Sun enters a sign in the Ptolemaic tropical zodiac, and a sign in the sidereal system proposed by Cyril Fagan . The beginning of Aries is defined as the moment of vernal equinox , and all other dates shift accordingly. The precise Gregorian times and dates vary slightly from year to year as
6708-617: The west, where If the above formula produces a negative value for A , it can be rendered positive by simply adding 360°. Again, in solving the tan( h ) equation for h , use of the two-argument arctangent that accounts for the quadrant is recommended. Thus, again consistent with the convention of azimuth being measured from the south and opening positive to the west, where These equations are for converting equatorial coordinates to Galactic coordinates. α G , δ G {\displaystyle \alpha _{\text{G}},\delta _{\text{G}}} are
6794-519: The zodiac as a means to determine astronomical measurement remained the main method for defining celestial positions by Western astronomers until the Renaissance, at which time preference moved to the equatorial coordinate system, which measures astronomical positions by right ascension and declination rather than the ecliptic-based definitions of celestial longitude and celestial latitude . The orientation of equatorial coordinates are aligned with
6880-428: The zodiac sign approximately to the corresponding constellation. This alignment needs re calibrating every so often to keep the alignment in place. The ecliptic intersects with 13 constellations of Ptolemy 's Almagest , as well as of the more precisely delineated IAU designated constellations . In addition to the twelve constellations after which the twelve zodiac signs are named, the ecliptic intersects Ophiuchus ,
6966-717: The zodiac, as found, e.g., in the Sefer Raziel HaMalakh . The zodiac is found in medieval stained glass as at Angers Cathedral , where the master glass maker, André Robin, made the ornate rosettes for the North and South transepts after the fire there in 1451. Astrology emerged in the 8th century AD as a distinct discipline in Islam, with a mix of Indian, Hellenistic Iranian and other traditions blended with Greek and Islamic astronomical knowledge, for example Ptolemy's work and Al-Sufi's Book of Fixed Stars. A knowledge of
7052-700: The zodiac, constellations north of the zodiac, and southern constellations. When Al-Sufi's book, and other works, were translated in the 11th century, there were mistakes made in the translations. As a result, some stars ended up with the names of the constellation they belong to (e.g. Hamal in Aries). The High Middle Ages saw a revival of interest in Greco-Roman magic , first in Kabbalism and later continued in Renaissance magic . This included magical uses of
7138-416: The zodiac, the average duration of the solar stay in each sign is one twelfth of a sidereal year , or 30.43 standard days . Due to Earth's slight orbital eccentricity , the duration of each sign varies appreciably, between about 29.4 days for Capricorn and about 31.4 days for Cancer (see Equation of time ). In addition, because the Earth's axis is at an angle, some signs take longer to rise than others, and
7224-483: 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
7310-413: 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
7396-413: Was to commence the zodiac from the point of the vernal equinox and to always refer to this point as "the first degree" of Aries. This is known as the "tropical zodiac" (from the Greek word trópos, turn) because its starting point revolves through the circle of background constellations over time. The principle of the vernal point acting as the first degree of the zodiac for Greek astronomers is described in
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