Why two panchangs disagree

Two honest panchangs can name different tithis on the same morning. The usual cause is the formula used for the Moon and the Sun, and then the rule that turns those longitudes into a civil day. A third cause is the month boundary. None of the three means that one household is careless. This note is about the difference, so a family can see why the uncle's sheet and the app on the phone do not match to the minute.

Astro's locked sky is drik plus Lahiri. A mode that reproduces one family's Surya Siddhanta panchang is a later choice, not this beta. Until the panchang page calculates, Astro also cannot show today's drik tithi for Dumka or for anywhere else.

Drik: positions that are computed

Drik means the positions are computed from a modern ephemeris and then shifted into the sidereal zodiac. The Government of India's Rashtriya Panchang, from the Positional Astronomy Centre in Kolkata, has been published in that form since 1957. It follows the Calendar Reform Committee of 1952 to 1955. Meghnad Saha chaired that committee. N. C. Lahiri was its secretary. Software in this line uses the Lahiri ayanamsa, also called Chitrapaksha.

The ayanamsa is the distance between the tropical zodiac, which is tied to the seasons and the March equinox, and the sidereal zodiac, which is tied to the stars. Indian calendars for festivals and kundli use the sidereal one. Lahiri is the standard offset in the Rashtriya Panchang and in most software a Dumka pandit actually runs. Other ayanamsas exist. They are not this beta.

An ephemeris answers a plain question: where is the Moon, in degrees, at this instant? The tithi, nakshatra, yoga, and karana are then arithmetic on those degrees. Sunrise for the city turns the arithmetic into a civil day. The quality of the panchang is the quality of those positions plus the honesty of the sunrise.

Drik replaces the printed ephemeris a pandit used to interpolate. The palm leaf stands for the older formula, not for a worse faith.

Vakya: the older formulas

Vakya, and the older Surya Siddhanta mean motions, are the formulas still printed in many temple and family panchangs. Tamil vakya is the best-known case. These are not guesses. They are mean-motion rules handed down and tabulated. They were the practical sky before a computer sat in the shop.

The end of a tithi or a nakshatra can differ from drik by minutes, and sometimes by hours. A public note of that gap is Drik Panchang's comparison of thiruganita and vakyam. The difference shows up exactly where families argue: the end time of an ekadashi, the sunrise tithi on a festival eve, the minute a muhurat closes. If one sheet says the tithi ended before sunrise and the other says it ended after, the English date of the vow can move by a day. Both printers may have done the arithmetic correctly inside their own formula.

The same phase, a small offset. Minutes here become a different morning when the offset crosses sunrise.

A difference of hours is often two formulas, not two mistakes.

The month boundary is a third split

Amanta months end at the new moon. The bright fortnight comes first, then the dark, and the month closes at Amavasya. Purnimanta months end at the full moon. The dark fortnight comes first, then the bright, and the month closes at Purnima. Much of North India speaks purnimanta names. Much of the south, and many computer defaults, speak amanta names.

Festivals can share one sky and wear two month names. Diwali's new moon is Kartik Amavasya in the usual North Indian count and Ashwin Amavasya in many amanta counts. Chhath's Shashthi, six bright days later, is Kartik Shukla Shashthi in both. The festival note keeps the North Indian names and flags the new-moon label where the schools diverge. Bringing an amanta month name into a purnimanta sentence, without saying so, is a good way to schedule the wrong week.

What to do when the sheets disagree

Read the colophon. A sheet that says Lahiri, or Chitrapaksha, or Rashtriya Panchang, is in the drik line. A sheet that says vakya, or Surya Siddhanta, or names a temple press your family has used for years, is in the other line. Pick one for the rite and stay with it for the end times. Do not take the tithi name from one and the minute from the other.

Astro will not silently average them. The locked choice is drik plus Lahiri, which is the sky a modern pandit's software is already close to. Matching a particular family vakya panchang to the minute is a later mode, and it should be named when it exists, so nobody thinks the two have become the same sheet.

A worked comparison without today's date

You can compare two schools without knowing this morning's tithi. Take any end time your family sheet prints, and ask only whether the other sheet puts that same end before or after the same sunrise. If both put it on the same side of sunrise, the civil date agrees and only the minutes differ. If they straddle sunrise, the mornings disagree, and the festival or the vrata can move by a day. That test needs the two sheets in hand. It does not need a blog to declare a winner, and it does not need Astro to publish a third time that splits the difference. Splitting the difference is a third formula nobody authorized. If you need a single minute for an invitation, pick the sheet the host household already uses and copy its end time whole. Say the name of that sheet on the card. Guests can then disagree with the school in the open, instead of discovering two clocks at the gate.

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