The traditional Hindu calendar (Panchang) relies on precise astronomical calculations rather than fixed clock hours. Central to this system are the Tithi (lunar day) and Muhurat (auspicious time window).
What is a Tithi?
A Tithi is defined by the angular distance between the Sun and the Moon as observed from Earth. Each Tithi represents a 12-degree increase in the longitudinal angle between the Moon and the Sun.
Because the Moon's velocity in its elliptical orbit varies, a Tithi does not equal a 24-hour solar day. A single Tithi can range anywhere from approximately 19 to 26 hours.
The Two Pakshas (Fortnights)
The lunar month is divided into two halves:
- Shukla Paksha (Waxing Phase): The 15 Tithis from New Moon (Amavasya) to Full Moon (Purnima).
- Krishna Paksha (Waning Phase): The 15 Tithis from Full Moon (Purnima) to New Moon (Amavasya).
How Muhurats Are Calculated
Unlike static clock intervals, auspicious time windows such as Abhijit Muhurat or Rahu Kaal are dynamically computed relative to local sunrise and sunset at your exact geographic location.
- Rahu Kaal: A 1/8th segment of the daytime period, considered inauspicious for starting new endeavors.
- Abhijit Muhurat: Midday window centered around local solar noon, ideal for important activities.
Chakra uses the Lahiri (Chitrapaksha) ayanamsa. The heavy astronomy runs once at build time (astronomy-engine); the site and app then apply local sunrise and the festival rules. No ephemeris ships in the pages. Rahu Kaal and Abhijit are slices of that local solar day, not fixed clock hours.