Pillar article
How a Sidereal Birth Chart Is Cast
A sidereal birth chart starts from the lagna, the sign rising at the birth city once the zone offset has been applied to the Julian day. Jyothish SI uses the Lahiri ayanamsa and Swiss Ephemeris for that calculation, then counts houses by sign.
Lagna, Moon, and the nine grahas
The lagna sign is the first house. The next sign is the second house, and so on around the twelve. That is whole-sign reckoning: a graha is in the house whose sign it occupies. The Moon's sign is the emotional ground and the point from which gochar is counted. The Sun's sign is authority and the father-karaka's dignity, and it changes about once a month. The Moon changes sign in a little over two days. The lagna changes sign in about two hours, which is why a wrong clock or a wrong city moves the entire house count. Rahu and Ketu are opposite each other. They rule no sign on the seven-lord list.
The Moon's nakshatra starts the clock
Twenty-seven nakshatras divide the sidereal zodiac. The lord of the nakshatra holding the Moon starts the Vimshottari sequence: Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, with lengths 7, 20, 6, 10, 7, 18, 16, 19, and 17 years. The first period is the balance left in that nakshatra, not a full mahadasha dropped on the birthday. A chart reading that names a mahadasha without the Moon's nakshatra is guessing. Daylight saving changes the zone offset and can change the lagna, and therefore nothing in the house count should be trusted until the birth place is the city, not merely the state.
What you can ask it on the first pass
Marriage is the 7th, its lord, and D9. Work is the 10th and its lord. Money splits into the 2nd for stores and the 11th for income. The body and the life as a whole are the lagna lord. A free Jyothish SI account can cast this kundli and chat about those houses. Paid plans add PDF reports, extra divisional charts, and WhatsApp transit alerts. The first pass is still the lagna, the Moon's nakshatra lord, and the mahadasha already running.
Frequently asked questions
Why does the birth city change the lagna?
Local time depends on the zone offset in minutes, applied before the Julian day. Two cities in one country can be in different zones, and daylight saving can shift the offset by an hour.
Does the Sun sign alone decode the chart?
The Sun's rashi is one graha. The lagna sets the houses, and the Moon's nakshatra sets the dasha. A month of birth is not a substitute for those two.
Which ayanamsa is used?
Lahiri. The chart is sidereal. A tropical ascendant from another system will not match these houses sign for sign.
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D1, D9, D10, dashas, yogas, and transits, the same calculations referenced in this article.