Lagna
The Ascendant: the zodiac sign rising at the eastern horizon for an exact time and location.
Definition
Lagna changes quickly with local sidereal time and depends strongly on birth time, latitude and longitude. In Whole Sign houses, the Lagna sign becomes House 1.
Example
A 15- or 20-minute birth-time change near a sign boundary can change Lagna while the slower planets remain nearly unchanged.
Accurate local time, timezone and coordinates are essential. A guessed birth time should not be presented with false precision.