Panchang in Chahārbāgh, Alborz Province, Iran Sat 20 Feb 2016

Shiva’s Pradosh puja is done in pradosha, the 3 muhurtas after sunset. Trayodashi runs from 19:26 on Fri 19 Feb to 19:46 on Sat 20 Feb, touching pradosha on both evenings. The Nirnayasindhu takes the evening it holds more of: Sat 20 Feb. 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, 06:49 here. Dwadashi ended at 19:26 Fri, before it. Trayodashi ends at 19:46, when the lead reaches 156°. The lead passed 0° at the new moon of 8 Feb, so the Moon is waxing: Shukla paksha.

The night of Fri 19 Feb ran from sunset 17:51 Fri to sunrise 06:49, 12 h 58 m. Cut into 15 muhurtas of 51 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 06:49 to 17:52, splits into 8 choghadiyas of 1 h 22 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 17:52 to 06:47 Sun, splits into 8 choghadiyas of 1 h 36 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′. Pushya spans 93°20′–106°40′; the Moon entered its pada 1 at 93°20′. It leaves at 01:59 Sun, for Ashlesha.

Add the Sun's and the Moon's places among the stars: 306.8° + 96.5° = 403.3°, one full turn and 43.3°. Past the turn, cut into 27 parts of 13°20′, it gives the yoga: 40°00′–53°20′ is the 4th, Saubhagya. It ends at 00:17 Sun, then Shobhana.

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 07:33, when the lead reaches 150°; Taitila until 19:46.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 06:49 to 06:47 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: Makara gives Magha. The Sun enters Kumbha on 13 Feb, inside the month. The next new moon, 9 Mar, finds it in Kumbha and begins Phalguna.

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 8 Feb, with the Sun in Makara, began Magha. This Shukla paksha reads Magha in both counts.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 20 Mar 2015, 13:06 Fri. Since then the Sun has moved 331.4° round the stars. Vikram Samvat numbers that year 2072; Shaka Samvat numbers it 1937.