Paksha

The Moon takes about 29.5 days to return to the same phase, and the Hindu calendar splits that cycle down the middle: each half is a paksha, a fortnight of fifteen tithis. Everything else in lunar time-keeping — the tithi names, the festival dates, the ritual calendar — depends on knowing which paksha you are in.

The two halves are named for what the Moon is doing. Shukla paksha, "the bright fortnight", runs from Amavasya (new moon) to Purnima (full moon) as the Moon waxes — its lit face growing night by night. Krishna paksha, "the dark fortnight", runs from Purnima back to Amavasya as the Moon wanes. The word krishna here means dark, not the deity, though the deity's birthday does fall in that half.

Worked example: a calendar shows Dwitiya on a given day. Which one? If the Moon is a thin waxing crescent two days past new moon, it is Shukla Dwitiya — the second tithi of the bright half. If the Moon is nearly new again, two days past the full moon, it is Krishna Dwitiya. Same name, different fortnight, different rituals — and the panchang distinguishes them every single time.

The halves carry different reputations. Shukla paksha is the growing half: tradition favours it for beginnings, expansion, purchases and anything meant to increase. Krishna paksha is the contracting half, preferred for settling debts, releasing old commitments and completion-type rituals — and it hosts Pitru Paksha, the ancestor fortnight. Amavasya itself is considered the pivot, auspicious for ancestor offerings but avoided for new ventures.

One practical wrinkle: in South Indian (amanta) reckoning, the month ends at Amavasya and the fortnight order is Shukla then Krishna; North Indian (purnimanta) reckoning ends the month at Purnima. The pakshas are identical — only which month they belong to shifts — a detail that explains most confusion when two calendars disagree on a festival date.