Astrology refers to any of several systems of understanding, interpreting and organizing knowledge about reality and human existence, based on the relative positions and movement of various real and construed celestial bodies, chiefly the Sun, Moon, planets, and lunar nodes as seen at the time and place of a birth or other event being studied. Common forms of astrology include Western astrology, Chinese astrology and Jyotish (vedic astrology). Western astrology is based on the tropical zodiac, while Jyotish is based on the sidereal zodiac.
Astrology is not the same as astronomy. Astronomers are often dismayed at being confused with their counterparts in astrology. Because they regard it as not adhering to standards of the scientific method mainstream Western scientists commonly consider astrology as a pseudoscience. Most astrologers, however, respect the knowledge gained from astronomy, and often incorporate it in their ideas.
Astrology was once deeply intertwined with astronomy, and a firm distinction between the two dates back only to the time of Galileo. He was one of the first to use the scientific method to test objective statements about the heavens by, for instance, using telescopic observations to show that astronomical bodies such as the sun and moon had markings on them, rather than being perfect, featureless spheres as maintained by Aristotle.
Astronomy aims to understand the physical workings of the universe, something of no particular interest to astrologers. Astrology, by contrast, attempts to draw connections between the physical motions of heavenly bodies and various events on earth, notably in the personal lives of individuals.
Many prominent figures in the early history of western astronomy, including Johannes Kepler and Galileo himself, also supported themselves by practising astrology for wealthy noblemen. Isaac Newton is sometimes cited as having an interest on astrology, but the proposed evidence does not stand up to close examination. There is not a single word recorded in Newton's hand that mentions the subject, and the handful of books in his possession that contained references to astrology were primarily concerned with other subjects.
There are some biological phenomena that are influenced by celestial movements (e.g. circadian rhythms, see Chronobiology). These results do not prove or disprove astrological claims, but suggest influences not fully understood. Scientific attempts to prove astrological influence have yielded negative or inconclusive results, for disputed reasons. Scientists would say astrology has no foundation in reality, and therefore cannot be proven. Astrologers would say scientists have designed the studies poorly because of an inadequate understanding of astrology.
Astrological concepts are pervasive in many societies, and endure despite strong efforts by scientists to discredit them. This is evidenced by the fact that influenza was so named because doctors once believed it to be caused by unfavorable planetary and stellar influences.