Location and time
All displayed times use Asia/Kolkata (IST, UTC +5:30). We support Chennai, Madurai, Coimbatore and Tiruchirappalli. Sunrise and sunset use the city-centre coordinates at sea level and Astronomy Engine’s apparent upper-limb rise/set model. Local terrain and elevation are not modelled.
The astronomical engine
We use the MIT-licensed Astronomy Engine 2.1.19 to calculate the Sun and Moon. Tithi boundaries are successive twelve-degree steps in the geocentric Moon–Sun ecliptic longitude difference. The daily sheet shows the tithi present at local sunrise and its ending time.
Tamil solar dates and nakshatram
This preview uses a linear Lahiri sidereal correction: 23.85675° at J2000 plus 50.29 arcseconds per tropical year. This is an approximation, not a full implementation of an independently certified panchangam. Nakshatram is the Moon’s sidereal longitude divided into twenty-seven equal parts. Its displayed ending time is found by a numerical search.
Where no reviewed boundary applies, the Tamil solar month is assigned using the Sun’s sidereal sign at Chennai sunset: an ingress after sunset begins the next civil day. We retain Chennai as the Tamil civil-date reference for all supported cities. Boundary dates and sidereal transition times require independent review before the preview can be promoted to an authoritative calendar.
For all of 2026, civil Tamil dates use month boundaries checked against the Federal Bank Tamil Calendar 2026. July–November boundaries were also reviewed using the Gnanananda panchangam, with Avani and Purattasi cross-checked against Prokerala’s Chennai calendar. Avani begins 18 August and Purattasi begins 18 September: 19 September is Purattasi 2. These civil boundaries take precedence over our approximate solar model; astronomical timings remain calculated.
For 2027, Thai, Masi, Panguni and Chithirai start dates (15 January, 13 February, 15 March and 14 April) agree in the Gnanananda panchangam and Prokerala’s Chennai calendar. Month starts from Vaikasi to Margazhi 2027 follow Prokerala’s Chennai calendar alone, because a printed panchangam for that period was not yet available when we checked on 11 October 2026. This moves Aani 1 to 15 June. We will re-check these dates against a printed panchangam when one is published.
Daytime intervals
Sunrise-to-sunset is divided into eight equal segments. Rahu Kalam, Yamagandam and Kuligai use the standard weekday segment mappings. These are location-based intervals, rather than the fixed ninety-minute slots found in some printed calendars. They are traditional classifications, not guarantees about an activity’s outcome.
Amavasai and Pournami
Our Special Days list contains the calculated tithi intervals. An entry is sorted by its start date, and both endpoints are shown. A monthly calendar marks each civil date touched by an interval. This does not select a fasting date, tarpanam date, or temple observance; those require additional tradition-specific rules.
Thirukkural of the day
The daily sheet shows the kurals of Aram and Porul (1 to 1,080) in order, one a day, starting with kural 1 on 1 January 2026. The Tamil text and G. U. Pope’s 1886 English translation come from an open compilation (tk120404/thirukkural), checked against Tamil Wikisource and Pope’s translation on Project Madurai. Some printed editions join or split words differently.
Traditional calendar details
Daytime Gowri periods divide local sunrise-to-sunset into eight equal parts. Weekday classifications follow the Drik Panchang Gowri table. The highlighted periods are favourable Gowri segments excluding Rahu Kalam. They are not the shorter, publisher-selected Nalla Neram hours printed in some calendars.
Soolam and Parigaram use the Tamil weekday convention documented by Golden Chennai. Day direction uses the sunrise nakshatra grouping described in this panchangam discussion; independent editorial review is still pending. These are traditional classifications.
The monthly tithi/star index lists values present at local sunrise. A tithi that starts and ends between successive sunrises will not appear in that index. It is not a list of prescribed fasting dates.
What we do not publish yet
The edition covers 2026–2027. Published festival, observance, Karinaal and general wedding dates are available under Special days with sources. These dates are separate from calculated tithi intervals. The 2027 holiday list is not yet included. Publisher-selected Nalla Neram hours, personalised marriage muhurtham times, star birthdays and daily horoscopes are not yet available.
Sources and corrections
Astronomy Engine provides the underlying astronomy. Our calculation version is drik-preview-1.1.0. Corrections are versioned and regenerated consistently across daily sheets and monthly views. Independent spot checks and their tolerances are recorded with the project; they do not replace a complete panchangam review.