What is a tithi?

A tithi is the time the Moon takes to pull 12 degrees ahead of the Sun. Thirty of those steps make a lunar month. The mean length is a little under a civil day, about twenty-three and a half hours. A real tithi runs shorter or longer than that, so it does not line up with midnight, and it does not line up with a printed English date.

That single fact is why most Hindu festivals move on the civil calendar. The festival is tied to a tithi. The English date is tied to the Sun. This note stays with the lunar day itself. The year's dates are a different question, and they wait for a panchang you trust.

Thirty names, two halves

The bright half is shukla paksha, from the new moon toward the full moon. The dark half is krishna paksha, from the full moon toward the next new moon. Each half has fifteen names.

Shukla runs Pratipada, Dwitiya, Tritiya, Chaturthi, Panchami, Shashthi, Saptami, Ashtami, Navami, Dashami, Ekadashi, Dwadashi, Trayodashi, Chaturdashi, and Purnima. Krishna repeats the first fourteen names and ends at Amavasya. Purnima is the full moon. Amavasya is the new moon.

People often say "the ekadashi" or "the ashtami" and stop. The name is incomplete until you know the paksha, and until you know which lunar month the panchang has assigned. Two schools name the month on a different boundary. Amanta months end at the new moon. Purnimanta months end at the full moon. The sky is one sky. The month label can be two labels. A vow that says "Kartik Shukla Ekadashi" has already chosen a school. A vow that says only "ekadashi" has not.

Shukla is the bright fortnight. Krishna is the dark fortnight. The same fourteen names appear in both.

How the 12 degrees are measured

The Sun and the Moon both move along the ecliptic. The Moon is faster. A tithi begins at a multiple of 12 degrees of elongation and ends at the next multiple. Amavasya is the stretch around 0 degrees, when the Moon is with the Sun. Purnima is the stretch around 180 degrees, when the Moon is opposite the Sun.

Because both bodies change speed, the time needed for 12 degrees is not constant. A short tithi can be near nineteen hours. A long one can pass twenty-six. Nothing in that variation is a moral fact. It is the geometry of two orbits.

The end time printed in a panchang is the instant the elongation reaches the next multiple, converted to the local clock. That instant is the same for the whole Earth. The clock reading is not, because timezones and the civil day differ. The sunrise rule, below, is what turns the instant into "today's tithi."

A tithi is 12 degrees of the Moon's gain on the Sun. The gap in the drawing is the idea, not a measurement for today.

Sunrise decides the name of the morning

The civil day in a panchang runs from sunrise to the next sunrise. If a tithi is in force at sunrise, that tithi is the day's tithi, even if it ends before breakfast. If one tithi covers two sunrises, it is the tithi of two civil days. If a tithi falls entirely between two sunrises, that civil day never wears its name.

Readers meet this as kshaya and vriddhi. A tithi that skips a sunrise is dropped from the civil list. A tithi that holds two sunrises is the name of two mornings. Families notice when a fast seems to fall on different dates in two towns. Near a boundary, Dumka and a city far west can honestly print different tithis on the same English date. The cause is the horizon.

Some vows do not use the sunrise tithi alone. They ask which tithi is running at a later hour, or they prefer the tithi that is current at the moment of the rite. A careful panchang states the rule for that vow. Guessing the rule is how a date gets argued in the courtyard.

The morning wears the tithi that is alive at sunrise, even when that tithi ends an hour later.

What a tithi is used for

Festivals, vrats, and many muhurats are pinned to a tithi rather than to a weekday alone. Ekadashi fasts follow the eleventh tithi. A wedding muhurat is a window inside a chosen tithi, read together with nakshatra, yoga, and weekday. The tithi is the spine. It is not, by itself, a promise that the act will succeed.

This note does not say which tithi is running today. Astro's panchang page is not calculating yet. Publishing "today is Shukla Panchami in Dumka" without that calculation would be a fiction. The festival note, separately, gives the usual tithi rules for Diwali, Chhath, Holi, Navratri, and Raksha Bandhan, and it gives no English date for 2026.

A short way to read the line

When you do have a panchang for your city, read the tithi line in this order. Read the paksha. Read the name. Read the end time, and notice whether that end is soon after sunrise or late in the next night. Then read the month name and remember which school printed it. If the end time is close to sunrise, look at the neighbouring town's sheet before you argue. If two sheets differ by hours, they may be drik and vakya, not a misprint. That difference has its own note.

Karana, the half that rides on the tithi

Each tithi holds two karanas. They are not a second lunar month. They are the tithi cut in half, so a long tithi has long karanas and a short tithi has short ones. A panchang that prints a karana is telling you which half is current and when it flips. Some muhurat lists treat a particular karana as unfit for a start. That is a rule of the list, not a property of the person. This note names the half so you can see it on the page. It does not rank the halves, and it does not print which half is running this morning.

A note on Astro is for understanding. It is a matter of belief and reflection. It is not a promise about health, death, money, or the law.

What Astro is, in this beta: https://astro.lawazia.tech/about