Pillar article
Tithi and Paksha: the Moon's Phase in Jyotish
A tithi is one phase of the Moon, defined as twelve degrees of elongation between the Moon and the Sun, and thirty tithis complete a lunar month. Shukla paksha runs from Amavasya toward Purnima as the Moon moves ahead of the Sun and gathers light. Krishna paksha runs from the full Moon back toward the dark Moon. Emotional cycles in a kundli follow this paksha and the natal Moon's sign, not a weekly column of Sun signs.
How a phase is measured
The Sun and Moon meet at Amavasya and stand opposite at Purnima. Between those meetings the Moon pulls ahead by about twelve degrees per tithi. Fifteen tithis fill each paksha. The eleventh, Ekadashi, and the fourth, Chaturthi, are familiar vow days because they are tithis, not weekdays. A tithi can begin in the afternoon and end the next morning, so the panchang day is the tithi in force at local sunrise. Two cities can observe different civil dates for the same tithi when sunrise falls near the change. India keeps Asia/Kolkata with no daylight saving, and sunrise still differs between Mumbai and Kolkata. A phase posted for one city is not automatically the phase in another.
Natal Moon versus today's phase
The birth tithi is a natal fact: how far the Moon had traveled from the Sun at the birth minute. A person born on Purnima has a full Moon in the chart. A person born on Amavasya has a Moon lost in the Sun's light, which classical texts treat as a Moon under pressure. Today's tithi is a transit of that same elongation and lasts only until the next twelve-degree step. Using today's phase to erase the natal Moon confuses a one-day panchang fact with a birth chart. The natal Moon's house still rules the mind. The running mahadasha, Moon's ten years or another lord's span, still rules the decade. A waxing week inside Saturn mahadasha does not become a Moon mahadasha.
Using the phase without a forecast mill
Muhurta prefers certain tithis for certain acts. Weddings avoid a handful of tithis and watch Bhadra, which is a karana problem inside the tithi. Emotional housekeeping can follow a simpler rule: Shukla paksha is the traditional half for beginnings that need light, Krishna paksha for endings, ancestor rites, and Amavasya observances such as Shani Jayanti when it falls on Jyeshtha Amavasya. Neither half diagnoses a mood disorder. If the natal Moon is debilitated in Vrishchika, the birth chart's mind is the lasting fact, and the paksha is only the month's lighting. Jyothish SI calculates the birth Moon from the city and time. The day's tithi still has to be read from a panchang for that city's sunrise.
Frequently asked questions
What is a tithi in degrees?
Twelve degrees of elongation between the Moon and the Sun. Thirty such steps make the lunar month, fifteen in Shukla paksha and fifteen in Krishna paksha.
Does today's Moon phase replace the birth Moon?
No. Today's tithi lasts until the next step of elongation. The natal Moon's sign, nakshatra, and dasha balance remain the birth chart.
Why do tithi dates differ by city?
The civil date follows the tithi at local sunrise. Sunrise differs by city, so a tithi that changes near dawn can fall on different calendar dates.
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D1, D9, D10, dashas, yogas, and transits, the same calculations referenced in this article.