Karwa Chauth falls on the Chaturthi of Krishna Paksha in Kartika. Married women keep a nirjala fast — without food or water — from before sunrise until the moon is sighted, for the long life of their husbands. It is among the strictest of the common vratas, and among the most precisely timed: it ends not at a clock hour but at moonrise, which shifts by city and by a few minutes each year.

The fast opens with sargi, a meal eaten before dawn, traditionally sent by the mother-in-law. It closes when the woman sees the moon through a sieve, then looks through the same sieve at her husband, and takes water from his hand.

The sieve is the detail that carries the meaning. The moon is looked at only through something that filters — and the husband is seen the same way, in the same light, immediately after.

The best-known story is of Veeravati, who kept the fast for her seven brothers' beloved sister. Unable to bear her hunger, the brothers lit a fire behind a tree and showed her its glow through a sieve as the 'moon'; she broke her fast — and word came that her husband had died. She refused to accept it, kept the vrat with full rigour the next year, and won him back from death. Older tellings reach further: Savitri arguing Satyavan's life back from Yama, and Draupadi keeping the fast on Krishna's counsel for the Pandavas.

Karwa Chauth falls in Kartik, as winter begins and the harvest year turns — traditionally the season of a bride's first months in a new home, which is part of why the bond it marks matters so. The pre-dawn sargi loads the body before a long day's fast; the moon, sighted after sunset through a sieve, gives the fast a precise, verifiable end rather than an arbitrary hour.

The vrat is a small, exacting tapasya offered for another's life rather than one's own — its whole weight is a turning of the self outward. The order of the evening carries the teaching: the moon is looked at first, through the sieve, and only then the husband's face — the beloved seen after, and through, a glimpse of the divine.

Veeravati was the only sister of seven devoted brothers. She kept her first Karwa Chauth fast and, by evening, was faint with thirst. Her brothers could not bear to watch. They lit a fire behind a peepal tree and held up a sieve before it, and told her the moon had risen. She looked, saw the glow, offered arghya and ate.

The moment the food touched her, word came that her husband was dead. She refused to accept it and sat by his body through the year, and when Karwa Chauth returned she kept the fast exactly, until the true moon. Parvati, moved, restored her husband to life. The story is told not as a warning against kind brothers but as an insistence on the one thing the vrat cannot bend on — the moon itself must be seen, and no likeness of it will serve.