The short version
- Ephemeris
- Swiss Ephemeris (JPL DE431-derived)
- Ayanamsa
- Lahiri / Chitrapaksha
- Zodiac
- Sidereal (nirayana)
- Reference location
- Kolkata — 22.5726° N, 88.3639° E
- Time zone
- Asia/Kolkata (IST, UTC+05:30)
- Tradition
- Drik siddhanta (observed positions)
- Bengali month rule
- Solar Sankranti, West Bengal convention
Positions and the ayanamsa
Solar and lunar positions come from the Swiss Ephemeris, the same ephemeris used by most professional astronomical software. It returns tropical longitudes; Indian calendrics needs sidereal ones, so the ayanamsa for the moment in question is subtracted from each.
The ayanamsa used here is Lahiri, also called Chitrapaksha — the value adopted by the Indian Calendar Reform Committee and used by the Rashtriya Panchang. It is the same basis as most Bengali drik panjikas, which is why the tithi and nakshatra boundaries on this site line up with them closely.
The ayanamsa is evaluated for the moment of sunrise on the day being shown, not for a fixed epoch. The difference is small but it is the correct treatment, and it matters near a boundary that falls within a few minutes of sunrise.
Tithi, nakshatra, yoga and karana
These are computed from the sidereal longitudes rather than looked up. A tithi is one twelfth of a sign of elongation between Moon and Sun; a nakshatra is one of the twenty-seven 13°20′ divisions the Moon occupies; a yoga comes from the sum of the two longitudes; a karana is half a tithi.
Because the Moon does not move at a constant rate, a tithi is not a fixed length — it runs anywhere from about 19 to about 26 hours. That is why a tithi can be skipped entirely on one day and repeat on another, and why the day a festival is observed is decided by which tithi is current at a specified moment rather than by which tithi the day “belongs to”.
Sunrise, sunset and the muhurta windows
Sunrise and sunset are true rise and set times computed topocentrically for the Kolkata coordinates above, with standard atmospheric refraction applied (1013.25 hPa, 15 °C). They are not a state-wide approximation.
Rahu Kalam, Kalbela, Kalratri, Amrita Yoga and Mahendra Yoga are all derived from that computed sunrise and sunset pair by the traditional divisions of the day and night, which is why they shift through the year rather than sitting at fixed clock times.
This is the figure most worth knowing about: because everything is computed for Kolkata, a reader elsewhere in West Bengal should expect a few minutes of difference. Siliguri sunrise runs several minutes later than Kolkata; the far west of the state later still. For most observances that is immaterial. For a muhurta measured in minutes, it is not.
How the Bengali month begins
The Bengali calendar is solar. A month begins when the Sun enters the corresponding sidereal sign — the Sankranti. This site computes the exact moment of each Sankranti from the ephemeris rather than using the nominal 14th/15th of the Gregorian month.
West Bengal and Bangladesh then apply different conventions for turning that instant into a calendar date. This site follows the West Bengal convention, under which the new month begins on the day following the transit. Bangladesh has used a fixed-length civil calendar since 1966 (revised 2019), so Bangladeshi dates will not always match what you see here, and are not what this site is computing.
Where this can disagree with your almanac
Bengali almanacs divide into two traditions. Drik or Visuddha Siddhanta panjikas use observed astronomical positions. Surya Siddhanta panjikas use the classical mean values, which have drifted from observation over the centuries.
This site is drik throughout. Against a drik panjika it should agree to the minute. Against a Surya Siddhanta panjika it can differ, occasionally by a whole tithi where a boundary falls near sunrise — which is exactly when a festival date can move by a day.
Neither tradition is an error. If this site disagrees with the almanac your family observes, follow your family's. What this page is for is letting you see why the two differ rather than leaving you to guess.
Common questions
Which ayanamsa does this Bengali calendar use?
Lahiri (Chitrapaksha) ayanamsa, the value adopted by the Indian Calendar Reform Committee and used by the Rashtriya Panchang. Sidereal longitudes are obtained by subtracting the ayanamsa for the moment of sunrise from the tropical longitude returned by the Swiss Ephemeris.
Which location are the timings calculated for?
All timings are computed for Kolkata at 22.5726° N, 88.3639° E, in Asia/Kolkata time. Sunrise and sunset are true topocentric rise and set times for that point, not a state-wide average, so a reader in Siliguri or Digha should expect a difference of several minutes.
Why does this panjika sometimes differ from a printed almanac?
Printed Bengali almanacs fall into two traditions. Drik (Visuddha Siddhanta) panjikas use observed astronomical positions and agree closely with this site. Surya Siddhanta panjikas use classical mean values and can differ by a tithi near a boundary. This site is drik throughout, so where it disagrees with a Surya Siddhanta almanac, follow whichever tradition your family observes.
Reporting a discrepancy
If a figure here looks wrong, it is worth reporting. Write to mailus.silly@gmail.com with the date, the value shown, the value you expected, and which panjika you are comparing against — that last detail usually settles whether it is a bug or a difference of tradition.