Your Moon sign is the rashi the Moon occupied at the moment of birth. All Vedic practice — horoscopes, dasha timing, marriage matching, naming — runs on this janma rashi, not on the Western date-based sun sign.
The computation uses Swiss Ephemeris: the Moon's sidereal longitude at your birth time and place, corrected by the Lahiri ayanamsa, is placed among the twelve 30° signs. The Moon changes sign every ~2¼ days — which is why time and place are asked along with the date.
How is the Moon sign different from the sun sign?
The sun sign comes from the birth month (Sun's position); the Moon sign from the Moon at the birth moment. In Vedic practice 'your rashi' almost always means the Moon sign — fasts, horoscopes and matching all use it.
What if I don't know my exact birth time?
The Moon is time-sensitive only on sign-boundary days; on most days morning and evening give the same rashi. On a boundary day the result shows both possibilities — refine the time by life-event matching then.
Why does a Western app show a different sign?
Western apps use the tropical zodiac, ~24° ahead of the sidereal — so the Vedic sign is usually one sign earlier. For Vedic prediction the sidereal reckoning is the scriptural one.
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