The Ascendant is the point of the ecliptic rising on the eastern horizon at the exact moment and place for which a chart is cast, formed where the ecliptic, the sun's apparent yearly path among the stars, crosses the plane of the local horizon on its eastward, ascending side. It is the cusp of the first house and one of the four angles, the points where the ecliptic meets the horizon and the celestial meridian.
The Ascendant is so central to the discipline that Hellenistic astrology took its own Greek name from it: the term was horoskopos, "hour-marker" or "hour-watcher," from hora, hour, and skopos, watcher, and this word is the direct root of the English "horoscope." It appears in the Greek text of Ptolemy's Tetrabiblos and, in the same second century, in the Anthologies of Vettius Valens, where the ascendant and midheaven together are called kentra, "centers" or angles, rendered in Latin as cardines. Because the Ascendant depends on the exact time and place of observation rather than the date alone, it was the technical device that let Hellenistic astrologers turn a table of planetary positions into a chart particular to one birth or event, distinct from a general almanac. Firmicus Maternus, writing his Latin Mathesis in the fourth century, names the ascendant among the cardines and calls it the best of the twelve places, ranking it above even the midheaven.