The Ascendant, called in Greek the horoskopos, the hour-marker, is the degree of the ecliptic rising over the eastern horizon at a given moment and place. It is not a body at all but a calculated point, and it is the single most important element in the classical system: the whole word horoscope comes from its Greek name, and the division of the chart into twelve houses is reckoned from it. Because the Earth turns once in twenty-four hours, the Ascendant moves through the entire zodiac in a day, about one degree every four minutes, which is why an accurate birth time matters and why astrology is sensitive to place as well as to time. The Ascendant governs the first house and is taken as the significator of the body, the appearance, the constitution and the native as an embodied person, and its ruling planet is the chart ruler.
Hellenistic technique gave the Ascendant a further role beyond signifying the body: it is the fixed reference point from which every one of the Hermetic lots, Fortune, Spirit and the rest, catalogued in this atlas among the Arabic parts, is projected, so that an error in the Ascendant's calculated degree propagates into every lot derived from it as well as into the house cusps themselves, making an accurate birth time the single most consequential piece of data a chart depends on.