Ascendant
The Ascendant (AC) is the zodiac sign — more precisely, the zodiac degree — rising on the eastern horizon at the moment of birth. It depends on the time and place of birth and shifts roughly every two hours.
While the Sun sign ("star sign") depends only on the date of birth, the Ascendant arises from Earth's rotation: over the course of 24 hours, all twelve zodiac signs rise once on the eastern horizon. The Ascendant is the intersection of the horizon and the ecliptic at the moment of birth — which is why calculating it strictly requires the birth time (ideally accurate to the minute) and the birthplace.
In astrological tradition, the Ascendant is linked to bearing, immediate presence, and the "threshold" over which a person meets the world; the Sun is assigned other themes there. Together with the Midheaven, the Ascendant forms one of the chart's two axes, and it's also the starting point for house counting in most house systems.
Without a reliable birth time, the Ascendant can't be determined precisely. Even a deviation of a few minutes shifts the degree value; close to a sign boundary, the sign itself can change. A value calculated from an estimated time must therefore be flagged as an approximation.
How we use this term
Leitstern calculates the Ascendant only when you provide a birth time — and leaves it out otherwise, rather than guessing. Leitstern deliberately doesn't use house systems.
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