Panchang in Chahārbāgh, Alborz Province, Iran Wed 20 Oct 2021

Purnima follows the tithi at sunrise. Purnima runs from 17:03 on Tue 19 Oct to 18:26 on Wed 20 Oct, so it holds sunrise only on Wed 20 Oct, at 06:17. No text giving Purnima’s time was found; sunrise is Tithika’s convention.

Purnima: every date in Chahārbāgh

The Moon gains on the Sun about 12° a day. Each 12° of lead is one tithi: 168°–180° is the 15th, Shukla Purnima. A day takes the tithi in force at its sunrise, 06:17 here. Chaturdashi ended at 17:03 Tue, before it. Purnima ends at 18:26, when the lead reaches 180°. The lead passed 0° at the new moon of 6 Oct, so the Moon is waxing: Shukla paksha.

The night of Tue 19 Oct ran from sunset 17:26 Tue to sunrise 06:17, 12 h 51 m. Cut into 15 muhurtas of 51 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 06:17 to 17:24, splits into 8 choghadiyas of 1 h 23 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 17:24 to 06:18 Thu, 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′. Revati spans 346°40′–360°00′; the Moon entered its pada 4 at 356°40′. It leaves at 12:01, for Ashwini.

Add the Sun's and the Moon's places among the stars: 182.8° + 357.1° = 539.9°, one full turn and 179.9°. Past the turn, cut into 27 parts of 13°20′, it gives the yoga: 173°20′–186°40′ is the 14th, Harshana. It ends at 18:38, then Vajra.

A karana is half a tithi: 6° of the Moon's lead, so the first half of Purnima is Vishti and the second Bava. Vishti ended at 05:41, when the lead reached 174°; Bava runs until 18:26.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 06:17 to 06:18 Thu, so the hours after midnight still belong to Budhawara.

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: Kanya gives Ashwina. The Sun enters Tula on 17 Oct, inside the month. The next new moon, 5 Nov, finds it in Tula and begins Kartika.

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 6 Oct, with the Sun in Kanya, began Ashwina. This Shukla paksha reads Ashwina in both counts.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 12 Apr 2021, 07:00 Mon. Since then the Sun has moved 184.5° round the stars. Vikram Samvat numbers that year 2078; Shaka Samvat numbers it 1943.