The Ascendant is the zodiac degree rising where the ecliptic meets the eastern horizon for a specific time and location. Its zodiac sign is commonly called the Rising sign. It is a calculated chart angle, not a planet or constellation.
Astrological traditions use the Ascendant to orient the houses and as a reflective symbol for approach, presence, or first response. Those meanings are interpretive conventions, not a scientific personality measure.
Because the horizon changes with time and place, an accurate Ascendant requires a reliable local birth time, coordinates, timezone handling, zodiac convention, and calculation method. A guessed time cannot support a definite result. If the time is unknown, a chart should omit or clearly mark the Ascendant and dependent houses.
The opposing western-horizon angle is the Descendant. The Sun, Moon, and Rising guide compares the Ascendant with the Sun sign and Moon sign.
Sources and further reading
The project methodology and pinned Astronomy Engine JavaScript reference document the coordinate calculation and required inputs. They do not establish the Ascendant’s traditional personality meanings.