Panchang in Myshkin, Yaroslavl Oblast, Russia Thu 20 Dec 2018

Shiva’s Pradosh puja is done in pradosha, the 3 muhurtas after sunset. Trayodashi runs from 03:56 on Thu 20 Dec to 02:04 on Fri 21 Dec, so only Thursday’s pradosha (15:38–19:08) falls within it. No text giving Pradosh Vrat’s time was found; pradosha is Tithika’s convention.

Pradosh Vrat: every date in Myshkin

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, 09:08 here. Dwadashi ended at 03:56, before it. Trayodashi ends at 02:04 Fri, when the lead reaches 156°. The lead passed 0° at the new moon of 7 Dec, so the Moon is waxing: Shukla paksha.

The night of Wed 19 Dec ran from sunset 15:38 Wed to sunrise 09:08, 17 h 30 m. Cut into 15 muhurtas of 1 h 10 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 09:08 to 15:38, splits into 8 choghadiyas of 48 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 15:38 to 09:08 Fri, splits into 8 choghadiyas of 2 h 11 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′. Krittika spans 26°40′–40°00′; the Moon entered its pada 2 at 30°. It leaves at 00:34 Fri, for Rohini.

Add the Sun's and the Moon's places among the stars: 244.2° + 31° = 275.2°. The sum, cut into 27 parts of 13°20′, gives the yoga: 266°40′–280°00′ is the 21st, Siddha. It ends at 16:54, then Sadhya.

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 15:05, when the lead reaches 150°; Taitila until 02:04 Fri.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 09:08 to 09:08 Fri, so the hours after midnight still belong to Guruwara.

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: Vrishchika gives Margashirsha. The Sun enters Dhanu on 16 Dec, inside the month. The next new moon, 6 Jan, finds it in Dhanu and begins Pausha.

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 7 Dec, with the Sun in Vrishchika, began Margashirsha. This Shukla paksha reads Margashirsha in both counts.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 17 Mar 2018, 16:11 Sat. Since then the Sun has moved 271.4° round the stars. Vikram Samvat numbers that year 2075; Shaka Samvat numbers it 1940.