Astrology.
Astrology is a group of systems, traditions, and beliefs in which knowledge of the 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, less often, an astrologist. Historically, the term mathematicus was used to denote a person proficient in astrology, astronomy, and mathematics.

Although the two fields share a common origin, modern astronomy is entirely distinct from astrology. Astronomy is the scientific study of astronomical objects and phenomena, whereas astrology is concerned with the attempt to correlate these phenomena with earthly affairs. Astrology is variously considered by its proponents to be a symbolic language, a form of art, science, or divination. The scientific community generally considers astrology to be a pseudoscience or superstition as astrologers have failed empirical tests in controlled studies. Despite the lack of scientific evidence, belief in astrology is widespread.

The word astrology is derived from the Greek αστρολογία, from άστηρ (aster, "star") and λόγος (logos, "speech, statement, reason"). The -λογία suffix is written in English as -logy, "study" or "discipline".

The main traditions used by modern astrologers are:
Chinese astrology
Jyotisha, Indian or Vedic astrology
Western astrology
Western astrology derives from the ancient Indian astrology and is a horoscopic systems of astrology and so is essentially similar in content. 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. The main difference between the two traditions is that Indian astrology continues to use the sidereal zodiac, linking the signs of the zodiac to their original constellations, while Western astrology uses the tropical zodiac (see section below). Because of the phenomenon 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 (and so to their Indian counterparts). In effect, in Western astrology the link between sign and constellation has been broken, whereas in Indian astrology it remains of paramount importance.

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. Also most notably and uniquely, 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 Japan, Vietnam, Thailand and other Asian countries.

In modern times, the three traditions have come into greater contact with each other. Chinese and Indian astrology have spread to the West, and awareness of Western astrology has increased in India and East Asia.