Pradoṣa vrata

Why it appears

Trayodaśī and early evening determine the date.

Trayodaśī means the thirteenth tithi. It occurs once in the bright fortnight and once in the dark fortnight, so this condition normally recurs twice in a lunar month. The observance is assigned to the local date on which Trayodaśī overlaps pradoṣa, the early-evening period after sunset.

Pradoṣa vrata centers on Śiva. It may include fasting, prayer, and worship according to a person's or community's tradition. The Marathi Viśvakoś describes this Trayodaśī observance, and Vera Lazzaretti's field study records it on the thirteenth day of each lunar fortnight at Kedār jī in Varanasi.

References: Marathi Viśvakoś on pradoṣa · Vera Lazzaretti, Here and Elsewhere, chapter 6

For this site, the pradoṣa period runs from local sunset until 144 minutes after sunset. Other pañcāṅgas may use a different boundary.

Śivarātri is another important Śiva observance with different timing rules.