The direct answer: What Is a Tithi? Lunar Day Explained: A tithi is twelve degrees of angular distance between Moon and Sun — the lunar day on a panchang, not a lucky or unlucky stamp. AskSoma publishes this at asksoma.ai/blog/what-is-a-tithi as a free Vedic astrology resource using Swiss Ephemeris calculations and classical Jyotish interpretation — not generic sun-sign copy.
A tithi is twelve degrees of angular distance between Moon and Sun — the lunar day on a panchang, not a lucky or unlucky stamp.
A tithi is twelve degrees of Moon-minus-Sun: one lunar day on a panchang, not a lucky stamp and not a curse day. Thirty tithis make a lunar month, Shukla first, then Krishna. AskSoma prints the running tithi from Swiss Ephemeris with Lahiri (Chitra Paksha) ayanamsa for one city. This page teaches the count. It does not rank days, sell a fast, or decide a marriage, a job, or a visa.
A tithi is not a midnight-to-midnight civil day. It is not a weekday. It is not a nakshatra. It is a span of elongation: the sidereal longitude of the Moon minus the sidereal longitude of the Sun, folded into thirty slices of twelve degrees. When that difference sits between 0° and 12°, the tithi is Shukla Pratipada. When it sits between 12° and 24°, Shukla Dwitiya. The arithmetic continues until 360°, which closes on Amavasya and starts the next bright fortnight.
That is the whole definition. The omen talk is extra. An adhik masa, when a lunar month is repeated, does not change the twelve-degree slice. It only adds another run of thirty names in that year. The count stays elongation, not a luck ladder.
AskSoma places the Sun and Moon with Swiss Ephemeris, then converts to the sidereal frame with Lahiri (Chitra Paksha) ayanamsa — the same stack as /panchang. See /methodology. A Western app that skips ayanamsa still has a Moon-minus-Sun number. That number is tropical elongation. Indian households use Lahiri names. Do not paste a tropical "lunar day" from a US wellness feed into an Ahmedabad jantri argument.
Because the Moon gains on the Sun at a changing speed, a tithi is not twenty-four hours. The live span can run from about twenty hours to about twenty-seven. That is why a tithi can start at 10:41am and end at 8:05am the next civil morning. "Aaj ka tithi" is a time range, not a label glued to midnight. If a site prints only the name and hides the start and end, it is wearing a calendar hat.
A lunar month has two pakshas. Shukla is the bright half: the Moon is waxing, elongation growing from the new-moon conjunction toward 180°. Krishna is the dark half: the Moon is waning, elongation growing from opposition toward the next conjunction.
The thirty names, in the order the sky actually makes them:
Purnima is the fifteenth of the bright half. Amavasya is the fifteenth of the dark half. Ekadashi is the eleventh of each paksha; this page will not rebuild the vrat list at /ekadashi. Chaturthi, Navami, and Chaturdashi are the Rikta set many electional screens treat as lean. Lean is a filter some houses apply when they have a choice. Lean is not a curse, and a Rikta tithi is not a command to stay in bed.
Do not flatten the thirty names into "good" and "bad." A pleasant nakshatra on a Rikta tithi is still a mixed row. This page names the lunar day. It does not rank your luck.
The sky's tithi is a range. The printed civil date is an assignment. Many North Indian and government-style panchangs use a simple rule: the tithi current at local sunrise is the name for that civil day. If Shukla Panchami is running at Bengaluru sunrise, the Bengaluru jantri prints Panchami on that Gregorian date, even if Panchami ends at 2:10pm and Shashthi occupies the evening.
That is why "what is today's tithi" and "which tithi is running right now" are different questions. A family that starts a small puja at 8:00pm may already be inside the next tithi while the wall calendar still shows the sunrise name. A vrata instruction that says "on Chaturthi" may mean the sunrise tithi, or the tithi current at the act. Ask which clock the instruction meant.
Some observances use moonrise or a pre-dawn watch. This explainer will not referee your sampradaya. The printed civil date is usually a sunrise stamp. The live limb is a start-and-end pair. Read both on /panchang.
Boston sunrise is not Bengaluru sunrise. Ahmedabad sunrise is not San Jose sunrise. London in August is a British Summer Time dawn, not an IST dawn. The assignment rule is the same sentence in each city. The instant it points at is not.
Because a tithi can be shorter or longer than the gap between two sunrises, the sunrise-assignment rule produces two calendar facts that scare people who wanted a tidy grid.
Kshaya tithi: the tithi starts after one local sunrise and ends before the next. It never owns a dawn. The printed civil calendar skips its name. The sky still ran that twelve-degree slice; the fridge magnet did not get a row. Families say the tithi was "lost." It was not stolen. It failed a sunrise test.
Vriddhi tithi: the same tithi is current at two consecutive local sunrises. The printed calendar shows that name on two civil dates. The slice was long enough to cover two dawns. Families say the tithi was "extra." It is still one elongation span, stamped twice.
Neither fact is a curse day. Neither fact is a lucky stamp. Both are what you get when a variable-length lunar day is forced onto a sunrise-to-sunrise civil list. A kshaya Ekadashi is a vrat-timing headache for /ekadashi and your priest, not a general omen. A vriddhi Chaturthi doubles a label on paper, not a future.
Tithi as elongation is sky-wide at one UTC instant. The Moon-minus-Sun number does not care whether you are standing in London or Ahmedabad. What changes with the city is the civil clock that labels the start and end, and the local sunrise that assigns the printed date.
Change the timezone and the clock labels move. A tithi that ends at 4:10pm in Ahmedabad may have already ended before a California morning puja starts — or may still have hours left. San Jose is roughly twelve and a half hours behind IST. Pasting a Delhi screenshot into a Bay Area group is the usual miss.
Change the longitude enough and a boundary can fall on different sides of sunrise. Bengaluru and Boston on the "same" Gregorian Thursday can print different sunrise tithis because their dawns are different instants. The sky agreed. The assignment did not.
Enter the city you are standing in, or the city where the rite will happen. Do not keep New Delhi as a default. A London flat reading an IST widget at breakfast is often already on the next tithi, or still on the previous one. The engine cares which coordinates and which IANA zone, including US daylight-saving transitions.
A panchang has five limbs: tithi, vara, nakshatra, yoga, karana. This page is the first limb only. The hub that prints all five for your city is /panchang. Overlays — Rahu Kaal, Choghadiya, Hora, Abhijit — are not tithis. Festival and vrat pages are derived from tithi, not the other way around.
AskSoma computes the Sun and Moon from Swiss Ephemeris with Lahiri ayanamsa. It cannot guarantee a marriage, a job, a visa, or a child's future. A tithi describes a lunar day. It does not rank your luck or clear a file at a consulate. If you already committed to a date, the tithi is information, not a veto.
Read today's tithi for the city you are in at /panchang. Set the place once. Read start and end, not just the name. Note sunrise if you need the printed civil assignment. Engine notes: /methodology.
Twelve degrees of Moon-minus-Sun: one lunar day on the panchang, a time range, not a midnight label and not a lucky stamp.
Because the Moon gains twelve degrees on the Sun at a changing speed, and that span is often shorter or longer than a civil day. Many tithis start or end mid-day. Read the range on /panchang.
Many printed panchangs name the civil date by the tithi current at local sunrise. The live limb can change later that day. Sunrise in Boston is not sunrise in Bengaluru. Ask which clock a vrata instruction meant.
Kshaya: the tithi misses both sunrises, so the civil calendar skips its name. Vriddhi: the tithi owns two sunrises, so the name prints twice. Both are calendar facts from variable length. Neither is a curse day.
Timezone labels move first. Longitude can also put a tithi end on different sides of local sunrise. A Delhi screenshot in a San Jose or London group is the usual miss. Set the city you are standing in.
No. A tithi is a lunar day. Rikta names are electional filters some houses use when they have a choice. AskSoma will not rank your luck, and it cannot guarantee a marriage, a job, or a visa.
Open /panchang, set the city, and read the tithi start and end. For the eleventh as a vrat list, use /ekadashi. For all five limbs, stay on the panchang hub. Engine: /methodology.
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Written by Savan Vyas, founder of AskSoma.
The astrology is not written from memory: every chart position, dasha period and panchang timing AskSoma shows is computed with the Swiss Ephemeris on the Lahiri (Chitrapaksha) ayanamsa. How we calculate.