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How Spasht calculates

Every number on Spasht is worked out, not copied. This page sets out how, so you can check it or disagree with it.

The astronomy

  • Ephemeris: Swiss Ephemeris, using its built-in Moshier model.
  • Zodiac: sidereal, with the Lahiri (Chitrapaksha) ayanamsa.
  • Places: local time comes from each city’s official time zone in force on that date, including clock changes.

The Hindu day

A Hindu day runs from one sunrise to the next, so tithis, nakshatras and moon events are reported for that span. That’s why a day can show “no moonrise” when the Moon rose just before dawn: that moonrise belongs to the previous Hindu day.

  • Sunrise and sunset: the Sun’s upper edge, with atmospheric refraction.
  • Moonrise and moonset: the centre of the Moon’s disc, with no refraction.

The five limbs

  • Tithi: each 12° the Moon gains on the Sun.
  • Vara: the weekday, which traditionally runs from sunrise to sunrise.
  • Nakshatra: the Moon’s position in 27 equal divisions of 13°20′.
  • Yoga: the Sun’s and Moon’s longitudes added together, in the same 27 divisions.
  • Karana: half a tithi, or each 6° the Moon gains.

The lunar month isn’t one of the five, but a panchang gives it too. It’s named from the Sun’s sign at the new moon that opens it. A month with no solar ingress is an extra month, Adhik Maas.

Traditional timings

Rahu Kaal, Yamaganda and Gulika each take one of eight equal parts of daylight, and which part depends on the weekday. Abhijit is the 8th of the day’s 15 muhurtas, and isn’t listed on Wednesdays. These are traditional rules we calculate faithfully. They aren’t astronomical events, and we know of no evidence that they affect outcomes.

Festival dates

Each festival is a lunar date plus the part of the day when it must be in force: Diwali needs Amavasya during Pradosh, Rama Navami needs Navami at midday, and so on. Holika Dahan and Raksha Bandhan also avoid Bhadra. Dates shown for other cities are calculated for that city, so they can differ.

How it’s tested

  • Daily panchang: compared with Drik Panchang on 8 dates in 5 cities, covering every weekday, London just after its clock change and New York in summer. Names and months match. Most times agree to within a minute. Tithi and karana ends run about a minute later than Drik, and agree to within 2.
  • Moon phases: compared with the US Naval Observatory’s published times.
  • Festival dates: compared with Drik Panchang’s New Delhi calendars for 2026–2030. Of the 90 dates compared, 89 match. The rules were adjusted using 2026–2028, so 2029–2030 are the fairer test: 35 of 36.
  • Consistency: every day of a year is calculated for 5 cities to catch gaps and clock-change errors.

These checks run automatically whenever the code changes.

Where we differ, and why

  • Tithi and karana ends usually fall about a minute later than Drik Panchang’s. Our times agree with the US Naval Observatory: it gives the new moon of 9 November 2026 as 07:02 UT, which is 12:32 IST. We show 12:32 and Drik Panchang shows 12:31.
  • Rama Navami 2029: we give 22 April; Drik Panchang lists 23 April. Traditions can differ on this festival, and Drik Panchang itself lists separate dates in some years.
  • Local practice wins. Regional panchangs and family traditions can differ from any calculation, including this one.

For a worked example of why sources disagree, read why Lakshmi Puja timings differ. Found a mistake? Tell us.