Pradoṣa Vrata

Pradoṣa (Pradosham) is the vrata of Lord Śiva observed on Trayodaśī, the thirteenth tithi, in both the waxing (śukla) and waning (kṛṣṇa) fortnights — so it recurs roughly twice a lunar month.

The observance centres on the pradoṣa-kāla, the hour and a half around sunset that is held the most auspicious time to worship Śiva. Devotees keep a fast through the day and break it after the evening worship.

The vrata takes a special name from the weekday it falls on — Soma Pradoṣa on a Monday, Bhauma (Aṅgāraka) Pradoṣa on a Tuesday, Śani Pradoṣa on a Saturday — each held in particular regard.

Here the Pradoṣa date is placed on the civil day whose sunset the Trayodaśī tithi covers, computed for your own location from the Swiss Ephemeris.