Panchang in Chahārbāgh, Alborz Province, Iran Sat 16 May 1981

Shiva’s Pradosh puja is done in pradosha, the 3 muhurtas after sunset. Trayodashi runs from 20:26 on Fri 15 May to 22:47 on Sat 16 May, touching pradosha on both evenings. The Nirnayasindhu takes the evening it holds more of: Sat 16 May. No text giving Pradosh Vrat’s time was found; pradosha is Tithika’s convention.

Pradosh Vrat: every date in Chahārbāgh

The Moon gains on the Sun about 12° a day. Each 12° of lead is one tithi: 144°–156° is the 13th, Shukla Trayodashi. A day takes the tithi in force at its sunrise, 05:00 here. Dwadashi ended at 20:26 Fri, before it. Trayodashi ends at 22:47, when the lead reaches 156°. The lead passed 0° at the new moon of 4 May, so the Moon is waxing: Shukla paksha.

The night of Fri 15 May ran from sunset 19:04 Fri to sunrise 05:00, 9 h 56 m. Cut into 15 muhurtas of 39 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 05:00 to 19:05, splits into 8 choghadiyas of 1 h 45 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 19:05 to 05:00 Sun, splits into 8 choghadiyas of 1 h 14 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The fixed stars divide the Moon's path into 27 nakshatras of 13°20′, each in 4 padas of 3°20′. Chitra spans 173°20′–186°40′; the Moon entered its pada 2 at 176°40′. It leaves at 19:38, for Swati.

Add the Sun's and the Moon's places among the stars: 31.5° + 179.4° = 210.9°. The sum, cut into 27 parts of 13°20′, gives the yoga: 200°00′–213°20′ is the 16th, Siddhi. It ends at 09:30, then Vyatipata.

A karana is half a tithi: 6° of the Moon's lead, so the first half of Trayodashi is Kaulava and the second Taitila. Kaulava runs until 09:36, when the lead reaches 150°; Taitila until 22:47.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 05:00 to 05:00 Sun, so the hours after midnight still belong to Shaniwara.

An amanta month runs from new moon to new moon and takes its name from the rashi the Sun is in at the new moon that begins it: Mesha gives Vaishakha. The Sun enters Vrishabha on 14 May, inside the month. The next new moon, 2 Jun, finds it in Vrishabha and begins Jyeshtha.

A purnimanta month runs from full moon to full moon, so its waning half comes first. It shares its name with the amanta month that its second half falls in: the new moon of 4 May, with the Sun in Mesha, began Vaishakha. This Shukla paksha reads Vaishakha in both counts.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 4 Apr 1981, 23:49 Sat. Since then the Sun has moved 40.1° round the stars. Vikram Samvat numbers that year 2038; Shaka Samvat numbers it 1903.