The same clock, a different sunrise
Chennai and Coimbatore both use IST, but the Sun does not rise at the same clock time in both cities. Their longitude and latitude differ. Our location selector changes the observer used for sunrise and sunset calculations.
Daylight does not always last twelve hours
Our Rahu Kalam, Yamagandam and Kuligai intervals use eight equal divisions of actual local daylight. As daylight changes through the year, the duration of each division changes too. A traditional fixed-clock chart and a sunrise-based calculation can therefore show different times.
Not every astronomical value changes by city
The lunar phase calculation here is geocentric: it uses the Moon and Sun as seen from Earth’s centre. Its transition occurs at the same instant for all four supported cities. The tithi present at sunrise can still differ because the local sunrise is different.
Why a printed calendar might disagree
Calendars may use different astronomical models, sidereal corrections, sunrise definitions or religious rules. A disagreement is something to investigate, not a reason to silently replace one value with another. Our preview publishes its calculation method and clearly identifies the parts still awaiting independent review.
What changes when you select a city
Local sunrise, sunset and daytime segments are recalculated for the chosen city. The Tamil civil date in this edition retains Chennai as its reference, so the month name and number stay consistent across the supported Tamil Nadu cities. This choice is documented on the method page.