Tithi vs Moon phase

Tithi is a calendar division of the Moon-Sun angle; Moon phase describes the changing illuminated appearance of the Moon.

They follow the same lunar cycle, but answer different questions. A phase name such as full Moon can refer to an exact astronomical instant. A tithi occupies a span of time.

Thirty steps through the cycle

Each tithi covers 12° of the Moon's longitude ahead of the Sun. Fifteen belong to waxing Shukla Paksha, and fifteen to waning Krishna Paksha.

Purnima (पूर्णिमा) is the final tithi of Shukla Paksha, ending when the Moon reaches 180° ahead of the Sun in longitude. That boundary is the full-Moon instant. Amavasya (अमावस्या) is the final tithi of Krishna Paksha, ending at the new-Moon conjunction.

Neither tithi is a fixed 24-hour day. A date labelled Purnima does not mean the exact full Moon occurs at midnight or lasts all day.

Why the Moon can look full on another date

Illumination changes continuously. The Moon can look nearly full before and after the exact full-Moon instant, while the tithi has already changed. The visible shape alone does not identify a precise tithi boundary.

Moonrise is another event: it describes the Moon crossing a local horizon. It need not coincide with a tithi change or the exact full Moon.

How to read the dashboard

The Tithi row shows the value at the city's sunrise, followed by its ending time. Moonrise and moonset have their own clock times. Read those fields separately rather than treating them as interchangeable phase indicators.

See the Panchang reading guide, or the Tithi and Moon rows on the Delhi dashboard.