What is Lagna (Ascendant)?
The lagna (also udaya lagna, ascendant) is the point of the zodiac rising on the eastern horizon at a particular instant and place. The rashi containing that point becomes the first house of a kundali, and every other house is counted from it.
How it is found
The Earth turns once in about 24 hours, so the entire zodiac rises past the eastern horizon in that time — roughly one rashi every two hours. Computing the lagna needs the exact instant plus the latitude and longitude: the same minute gives different lagnas in Chennai and in Delhi. Being the fastest-moving element of a chart, it is also the one an inexact birth time damages first.
Rashis do not rise for equal times
Two hours per rashi is an average, not a rule. The ecliptic meets the horizon at an angle that changes through the day, so some rashis take well over two hours to rise and others well under — and the disparity grows with latitude. This is why lagna tables are computed for a place rather than read off a clock.
Why it anchors everything else
Bhavas are counted from the lagna, so the lagna decides which house every graha lands in. Two people born on the same day in the same city, two hours apart, share nearly identical graha positions and yet get completely different house placements — and rules that depend on houses, Mangal Dosha among them, change with it.
Lagna and muhurta
Lagna is not only a birth quantity. Choosing an auspicious lagna for the moment of a ceremony is a standard part of muhurta, which is why an almanac prints the day’s lagna timings alongside its choghadiya and hora tables.
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FAQ
How often does the lagna change?
About every two hours on average — twelve rashis across roughly 24 hours — but the actual span of each rashi varies with the season and your latitude.
Is lagna the same as the moon sign?
No. The lagna is the rashi rising in the east at the birth moment; the moon sign (chandra rashi) is the rashi the Moon itself occupies. A chart carries both.
Does lagna depend on the birth place?
Yes. It is defined by the local horizon, so latitude and longitude both enter the calculation.