Astrology (from Greek ἄστρον, astron, "constellation, star"; and -λογία, -logia, "the study of") is a group of systems, traditions, and beliefs in which knowledge of the apparent relative positions of celestial bodies and related details is held to be useful in understanding, interpreting, and organizing information about personality, human affairs, and other terrestrial matters. A practitioner of astrology is called an astrologer or an astrologist. Numerous traditions and applications employing astrological concepts have arisen since its earliest recorded beginnings in the 3rd millennium BC. It has played a role in the shaping of culture, early astronomy, and other disciplines throughout history.
Astrology and astronomy were often indistinguishable before the modern era, with the desire for predictive and divinatory knowledge one of the primary motivating factors for astronomical observation. Astronomy began to diverge from astrology after a period of gradual separation from the Renaissance up until the 18th century. Eventually, astronomy distinguished itself as the scientific study of astronomical objects and phenomena without regard to the astrological speculations of these phenomena.
Astrology can be defined as the study of the positions of celestial bodies in the belief that their movements either directly influence life on Earth or correspond somehow to events experienced on a human scale. Modern astrologers define astrology as a symbolic language, an art form, and a form of divination. Despite differences of definitions, a common assumption of astrology is the use of celestial placements in order to explain past and present events and predict the future. Generally, the scientific community considers astrology a pseudoscience or superstition. Despite its rejection by virtually all scientists, 31% of Americans polled expressed a belief in astrology and 39% considered it scientific according to another study.
 Core beliefs
The core beliefs of astrology were prevalent in most of the ancient world and are epitomized in the Hermetic maxim "as above, so below". Tycho Brahe used a similar phrase to summarize his studies in astrology: suspiciendo despicio, "by looking up I see downward". Although the principle that events in the heavens are mirrored by those on Earth was once generally held in most traditions of astrology around the world, in the West there has historically been a debate among astrologers over the nature of the mechanism behind astrology. The debate also covers whether or not celestial bodies are only signs or portents of events, or if they are actual causes of events through some sort of force or mechanism.
Although the connection between celestial mechanics and terrestrial dynamics was explored first by Isaac Newton with his development of a universal theory of gravitation, claims that the gravitational effects of the celestial bodies are what accounts for astrological generalizations are not substantiated by scientific research, nor are they advocated by most astrologers.
Most astrological traditions are based on the relative positions and movements of various real or construed celestial bodies and on the construction of implied or calculated celestial patterns as seen at the time and place of the event being studied. These are chiefly the astrological planets, dwarf planets, the asteroids, the stars, the lunar nodes, Arabic parts and hypothetical planets. The frame of reference for such apparent positions is defined by the tropical or sidereal zodiac of twelve signs on one hand, and by the local horizon (ascendant-descendant axis) and midheaven-imum coeli axis on the other. This latter (local) frame is typically further divided into the twelve astrological houses. Furthermore, the astrological aspects are used to determine the geometric/angular relationship(s) between the various celestial bodies and angles in the horoscope.
The claim of astrology to predict future trends and developments, or predictive astrology, is based on two main methods in western astrology: astrological transits and astrological progressions. In astrological transits the ongoing movements of the planets are interpreted for their significance as they transit through space and the horoscope. In astrological progressions the horoscope is progressed forward in time according to set methods. In vedic astrology the focus is on planetary periods to infer the trend while transits are used to time significant events. Most western astrologers no longer try to forecast actual events, but focus instead on general trends and developments. By comparison, vedic astrologers predict both trends and events. Skeptics respond that this practice of western astrologers allows them to avoid making verifiable predictions, and gives them the ability to attach significance to arbitrary and unrelated events, in a way that suits their purpose.
In the past, astrologers often relied on close observation of celestial objects and the charting of their movements. Modern astrologers use data provided by astronomers which are transformed to a set of astrological tables called ephemerides, showing the changing zodiacal positions of the heavenly bodies through time.
There are many traditions of astrology, some of which share similar features due to the transmission of astrological doctrines between cultures. Other traditions developed in isolation and hold different doctrines, though they too share some features due to drawing on similar astronomical sources.
 Current traditions
The main traditions used by modern astrologers are:
Vedic and Western astrology share a common ancestry as horoscopic systems of astrology, in that both traditions focus on the casting of an astrological chart or horoscope, a representation of celestial entities, for an event based on the position of the Sun, Moon, and planets at the moment of the event. However, Vedic astrology uses the sidereal zodiac, linking the signs of the zodiac to their original constellations, while Western astrology uses the tropical zodiac. Because of the precession of the equinoxes, over the centuries the twelve zodiacal signs in Western astrology no longer correspond to the same part of the sky as their original constellations. In effect, in Western astrology the link between sign and constellation has been broken, whereas in Vedic astrology it remains of paramount importance. Other differences between the two traditions include the use of 27 (or 28) nakshatras or lunar mansions, which have been used in India since Vedic times, and the system of planetary periods known as dashas.
In Chinese astrology a quite different tradition has evolved. By contrast to Western and Indian astrology, the twelve signs of the zodiac do not divide the sky, but rather the celestial equator. The Chinese evolved a system where each sign corresponds to one of twelve 'double-hours' that govern the day, and to one of the twelve months. Each sign of the zodiac governs a different year, and combines with a system based on the five elements of Chinese cosmology to give a 60 (12 x 5) year cycle. The term Chinese astrology is used here for convenience, but it must be recognised that versions of the same tradition exist in Korea, Japan, Vietnam, Thailand and other Asian countries.
In modern times, these traditions have come into greater contact with each other, notably with Indian and Chinese astrology having spread to the West, while awareness of Western astrology is still fairly limited in Asia. Astrology in the Western world has diversified greatly in modern times. New movements have appeared, which have jettisoned much of traditional astrology to concentrate on different approaches, such as a greater emphasis on midpoints, or a more psychological approach. Some recent Western developments include:
- Modern tropical and sidereal horoscopic astrology
- Psychological astrology
- Sun sign astrology
- Hamburg School of Astrology
- Uranian astrology, subset of the Hamburg School
 Historical traditions
Throughout its long history, astrology has come to prominence in many regions and undergone developments and change. There are many astrological traditions that are historically important, but which have largely fallen out of use today. Astrologers still retain an interest in them and regard them as an important resource. Historically significant traditions of astrology include:
- Arab and Persian astrology (Medieval, near East)
- Babylonian astrology (Ancient, near East)
- Egyptian astrology
- Hellenistic astrology (Classical antiquity)
- Mayan astrology
The history of Western, Chinese, and Indian astrology is discussed in the main article history of astrology.
 Esoteric traditions
Many mystic or esoteric traditions have links to astrology. In some cases, like Kabbalah, this involves participants incorporating elements of astrology into their own traditions. In other cases, like divinatory tarot, many astrologers themselves have incorporated the tradition into their own practice of astrology. Esoteric traditions include, but are not limited to:
- Kabbalistic astrology
- Medical astrology
- Rosicrucian or "Rose Cross"
- Tarot divination
Historically, alchemy in the Western World was particularly allied and intertwined with traditional Babylonian-Greek style astrology; in numerous ways they were built to complement each other in the search for occult or hidden knowledge. Astrology has used the concept of the four classical elements of alchemy from antiquity up until the present day. Traditionally, each of the seven planets in the solar system known to the ancients was associated with, held dominion over, and "ruled" a certain metal.
 The zodiac
The zodiac is the belt or band of constellations through which the Sun, Moon, and planets transit across the sky. Astrologers noted these constellations and so attached a particular significance to them. Over time they developed the system of twelve signs of the zodiac (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces), based on twelve of the constellations they considered to be particularly important. The Western and Vedic zodiac signs have a common origin in the tradition of horoscopic astrology, and so are very similar in meaning. In China on the other hand, the development of the zodiac was different. Although the Chinese too have a system of twelve signs (named after animals), the Chinese zodiac refers to a pure calendrical cycle, as there are no equivalent constellations linked to it like the Western or Indian zodiacs. The common choice of twelve zodiac signs is understandable considering the interaction of the Sun and Moon was central to all forms of astrology.
The majority of Western astrologers base their work on the tropical zodiac which divides the sky into twelve equal segments of 30 degrees each, beginning with the first point of Aries, the point where the line of the Earth's celestial equator and the ecliptic (the Sun's path through the sky) meet at the northern hemisphere spring equinox. Due to the precession of the equinoxes, the slow changing of the way Earth rotates in space, the zodiacal signs in this system bear no relation to the constellations of the same name but stay aligned to the months and seasons.
Practitioners of the Vedic astrological tradition and a minority of Western astrologers use the sidereal zodiac. This zodiac uses the same evenly divided ecliptic but approximately stays aligned to the positions of the observable constellations with the same name as the zodiacal signs. The sidereal zodiac differs from the tropical zodiac by an offset called the ayanamsa, which steadily increases as the equinoxes drift further. Furthermore, some siderealists (i.e. astrologers employing sidereal techniques) use the actual, unequal constellations of the zodiac in their work.
 Horoscopic astrology
Horoscopic astrology is a system that was developed in the Mediterranean region and specifically Hellenistic Egypt around the late 2nd or early 1st century BCE. The tradition deals with two-dimensional diagrams of the heavens, or horoscopes, created for specific moments in time. The diagram is then used to interpret the inherent meaning underlying the alignment of celestial bodies at that moment based on a specific set of rules and guidelines. A horoscope was calculated normally for the moment of an individual's birth, or at the beginning of an enterprise or event, because the alignments of the heavens at that moment were thought to determine the nature of the subject in question. One of the defining characteristics of this form of astrology that makes it distinct from other traditions is the computation of the degree of the Eastern horizon rising against the backdrop of the ecliptic at the specific moment under examination, otherwise known as the ascendant. Horoscopic astrology has been the most influential and widespread form of astrology across the world, especially in Africa, India, Europe, and the Middle East, and there are several major traditions of horoscopic astrology whose origins are Hellenistic, including Indian, Medieval, and most other modern Western traditions of astrology.
 The horoscope
Central to horoscopic astrology and its branches is the calculation of the horoscope or astrological chart. This two-dimensional diagrammatic representation shows the celestial bodies' apparent positions in the heavens from the vantage of a location on Earth at a given time and place. The horoscope is also divided into twelve different celestial houses which govern different areas of life. Calculations performed in casting a horoscope involve arithmetic and simple geometry which serve to locate the apparent position of heavenly bodies on desired dates and times based on astronomical tables. In ancient Hellenistic astrology the ascendant demarcated the first celestial house of a horoscope. The word for the ascendant in Greek was horoskopos from which horoscope derives. In modern times, the word has come to refer to the astrological chart as a whole.
 Branches of horoscopic astrology
Traditions of horoscopic astrology can be divided into four branches which are directed towards specific subjects or purposes. Often these branches use a unique set of techniques or a different application of the core principles of the system to a different area. Many other subsets and applications of astrology are derived from these four fundamental branches.
- Natal astrology, the study of a person's natal chart to gain information about the individual and his/her life experience.
- Katarchic astrology, which includes both electional and event astrology. The former uses astrology to determine the most auspicious moment to begin an enterprise or undertaking, and the latter to understand everything about an event from the time at which it took place.
- Horary astrology, used to answer a specific question by studying the chart of the moment the question is posed to an astrologer.
- Mundane or world astrology, the application of astrology to world events, including weather, earthquakes, and the rise and fall of empires or religions. This includes the Astrological Ages, such as the Age of Aquarius, Age of Pisces and so on. Each age is about 2,150 years in length and many people believe these massive ages correspond to major historical events and current developments in the world
 History of astrology
The origins of much of the astrological doctrine and method that would later develop in Asia, Europe, and the Middle East are found among the ancient Babylonians and their system of celestial omens that began to be compiled around the middle of the 2nd millennium BCE. This system of celestial omens later spread either directly or indirectly through the Babylonians and Assyrians to other areas such as India, Middle East, and Greece where it merged with pre-existing indigenous forms of astrology.This Babylonian astrology came to Greece initially as early as the middle of the 4th century BCE, and then around the late 2nd or early 1st century BCE after the Alexandrian conquests, this Babylonian astrology was mixed with the Egyptian tradition of decanic astrology to create horoscopic astrology. This new form of astrology, which appears to have originated in Alexandrian Egypt, quickly spread across the ancient world into Europe, the Middle East and India.
 Before the modern era
The differentiation between astronomy and astrology varied from place to place; they were strongly linked in ancient India, ancient Babylonia and medieval Europe, but separated to an extent in the Hellenistic world. The first semantic distinction between astrology and astronomy was given in the 11th century by the Persian astronomer, Abū Rayhān al-Bīrūnī (see astrology and astronomy).
The pattern of astronomical knowledge gained from astrological endeavours has been historically repeated across numerous cultures, from ancient India through the classical Maya civilization to medieval Europe. Given this historical contribution, astrology has been called a protoscience along with pseudosciences such as alchemy (see "Western astrology and alchemy" below).
Astrology was not always uncritically accepted before the modern era; it was often challenged by Hellenistic skeptics, church authorities, and medieval Muslim astronomers, such as Al-Farabi (Alpharabius), Ibn al-Haytham (Alhazen), Abū Rayhān al-Bīrūnī, Avicenna and Averroes. Their reasons for refuting astrology were often due to both scientific (the methods used by astrologers being conjectural rather than empirical) and religious (conflicts with orthodox Islamic scholars) reasons.Ibn Qayyim Al-Jawziyya (1292-1350), in his Miftah Dar al-SaCadah, used empirical arguments in astronomy in order to refute astrology and divination.
Many prominent thinkers, philosophers and scientists, such as Pythagoras, Plato, Aristotle, Galen, Paracelsus, Girolamo Cardan, Nicholas Copernicus, Taqi al-Din, Tycho Brahe, Galileo Galilei, Johannes Kepler, Carl Jung and others, practiced or significantly contributed to astrology.
 Modern approaches
Several innovations have occurred in astrological practice in modern times.
 Western astrology
- During the middle of the 20th century, Alfred Witte and following him Reinhold Ebertin pioneered the use of midpoints (midpoints in Astrology) in horoscopic analysis.
- From the 1930s to the 1980s, astrologers including Dane Rudhyar, Liz Greene and Stephen Arroyo pioneered the use of astrology for psychological analysis, with some following the lead of psychologists like Carl Jung.
- In the 1930s, Don Neroman developed and popularised in Europe a form of Locational Astrology under the name of "Astrogeography." In the 1970s, American astrologer Jim Lewis developed and popularized a different approach under the name of Astrocartography. Both methods purport to identify varying life conditions through differences in location.
 Vedic astrology
- In the 1960s, H.R. Seshadri Iyer, introduced a system including the yoga point, which became popular in the West.
- From the early 1990s, Indian vedic astrologer and author, V.K. Choudhry has created and developed the Systems' Approach for Interpreting Horoscopes, a simplified system of Jyotish (predictive astrology). The system, also known as "SA", helps those who are trying to learn Jyotisha.
- The late K. S. Krishnamurti developed the Krishnamurti Paddhati system based on the analysis of the stars (nakshatras), by sub-dividing the stars in the ratio of the dasha of the concerned planets. The system is also known as "KP" and "sub theory".
 Effects on world culture
Astrology has had a profound influence over the past few thousand years on Western and Eastern cultures. In the Middle Ages, when the educated of the time believed in astrology, the system of heavenly spheres and bodies was believed to reflect on the system of knowledge and the world itself below.
Astrology has had an influence on both language and literature. For example, influenza, from medieval Latin influentia meaning influence, was so named because doctors once believed epidemics to be caused by unfavorable planetary and stellar influences. The word "disaster" comes from the Italian disastro, derived from the negative prefix dis- and from Latin aster "star", thus meaning "