The Ascendant orients an entire chart to one specific time and place, which is why two people born on the same day, even in the same city, can have noticeably different horoscopes once the hour is taken into account. Because the eastern horizon carries the whole ecliptic past it roughly once every twenty four hours, the Ascendant shifts by about one degree every four minutes, making it one of the most time sensitive points a chart uses. It served as a foundational device of Hellenistic horoscopy from at least the second century CE, when it is recorded under its Greek name, horoskopos, in the works of Vettius Valens and Claudius Ptolemy; Ptolemy's Tetrabiblos even devotes a chapter to the influence of the four angles the Ascendant heads.
In Latin astrological writing, such as the Mathesis of Firmicus Maternus, the same point appears among the cardines, the Latin term for the angles that survives in modern usage as the "cardinal" points of a chart. In current notation the Ascendant is abbreviated AC or Asc, and it is conventionally drawn at the nine o'clock position on the now standard circular wheel chart, a diagramming convention that itself replaced older square format horoscopes, used across Western, Indian and Chinese astrology for centuries, only around the nineteenth century.