What is lagna (ascendant), and why does it matter so much?

lagna is the sign rising on the eastern horizon at your birth; it fixes the first house and so the whole chart.

As the Earth turns, all twelve signs rise one after another on the eastern horizon in about 24 hours, so each sign rises for roughly two hours. The sign rising at the moment and place of your birth is your lagna, or ascendant. It becomes the first house, and the other eleven houses — wealth, siblings, home, children, marriage, career and so on — are counted from it.

This is why classical texts give lagna the highest place: the same planets fall in different houses for two people born a few hours apart on the same day. The Moon rāśi describes the mind; the lagna describes the body, temperament and the overall frame of life.

Because the lagna changes every couple of hours, an accurate birth time and place are essential for reading it.

Source: Bṛhat Parāśara Horā Śāstra; Bṛhat Jātaka · Each sign rises for about 2 hours

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