What is the Lagna (ascendant)?
Lagna is the ascendant: the sign and degree of the zodiac rising on the eastern horizon at the moment of birth.
What it is
The Lagna sets house 1 and changes about every two hours, because the sky turns once a day and the signs rise one after another. It is the reference point for the whole chart.
How it is worked out or read
The Lagna is found from local sidereal time and latitude. The method is on the lagna pages and the method page. It needs an exact birth time, so a time error of a few minutes can change the sign if the birth is close to a boundary.
Where it appears on this site
The Lagna is shown at the top of the birth chart. See how the Lagna is calculated.
Why the Lagna changes so quickly
The Lagna is the sign rising on the eastern horizon, and the sky turns once a day. With twelve signs rising in a day, each sign takes roughly two hours to rise, which is why the Lagna changes about every two hours. That rate is what makes birth time so important. Two children born in the same hospital ten minutes apart may have different Lagnas if the boundary falls between their times. A reader should always ask whether the birth time is exact, and say how exact, before using the Lagna for house-based reading.
Lagna and the other reference points
In practice, a reader compares the Lagna with the Moon sign and the Sun sign. The Lagna is the reference for houses in the whole-sign system. The Moon sign is the reference for the Moon-based rules, such as Kemadruma and the Moon-based houses used in some checks. The Sun is used in the tithi and in the Budhaditya yoga. A complete reading names all three, and says which rule uses which. Treating the Lagna as the only reference point is a common oversimplification.
Lagna and sunrise
The Lagna is related to the sunrise but is not the same thing. At sunrise the Sun is rising in the east, and the sign then on the horizon is the Lagna of a birth at that moment. A birth at sunrise therefore has a Lagna close to the Sun's position, usually in the same sign but not always. Readers who think the Lagna is simply the Sun's sign are making a common mistake; the two are close at sunrise but are not the same measurement.
Lagna in the daily sky
The Lagna changes through the day as the zodiac rises, so a reader can watch the sky at dawn and see the sign rising on the eastern horizon. Seeing it once makes the abstract idea of the Lagna concrete and helps a reader understand why the birth time matters.
Lagna and the rising horizon
The Lagna is the point of the zodiac on the eastern horizon at birth, and it is often pictured as a window through which the chart looks out onto the world. A reader may use this image to remember that the Lagna sets the frame, and the grahas are seen through it.