Astrology is a group of systems, traditions, and beliefs in which knowledge of the relative positions of celestial bodies and related information is held to be useful in understanding, interpreting, and organizing knowledge about personality, human affairs, and other terrestrial events. A practitioner of astrology is called an astrologer, or, less often, an astrologist.
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. 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, however, the word has come to refer to the astrological chart as a whole.