Panchang in Chahārbāgh, Alborz Province, Iran Sun 22 Aug 2021

The rakhi is tied in aparahna, the fourth fifth of the day, outside bhadra. Purnima runs from 18:00 on Sat 21 Aug to 16:31 on Sun 22 Aug, so it touches only Sunday’s aparahna (14:29–17:08). Every reading takes that day.

Raksha Bandhan: every date in Chahārbāgh

Purnima follows the tithi at sunrise. Purnima runs from 18:00 on Sat 21 Aug to 16:31 on Sun 22 Aug, so it holds sunrise only on Sun 22 Aug, at 06:30. 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, 06:30 here. Chaturdashi ended at 18:00 Sat, before it. Purnima ends at 16:31, when the lead reaches 180°. The lead passed 0° at the new moon of 8 Aug, so the Moon is waxing: Shukla paksha.

The night of Sat 21 Aug ran from sunset 19:49 Sat to sunrise 06:30, 10 h 41 m. Cut into 15 muhurtas of 42 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 06:30 to 19:47, splits into 8 choghadiyas of 1 h 39 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 19:47 to 06:31 Mon, splits into 8 choghadiyas of 1 h 20 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′. Dhanishtha spans 293°20′–306°40′; the Moon entered its pada 2 at 296°40′. It leaves at 18:39, for Shatabhisha.

Add the Sun's and the Moon's places among the stars: 125.1° + 299.7° = 424.8°, one full turn and 64.8°. Past the turn, cut into 27 parts of 13°20′, it gives the yoga: 53°20′–66°40′ is the 5th, Shobhana. It ends at 09:33, then Atiganda.

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 05:13, when the lead reached 174°; Bava runs until 16:31.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 06:30 to 06:31 Mon, so the hours after midnight still belong to Raviwara.

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: Karka gives Shravana. The Sun enters Simha on 17 Aug, inside the month. The next new moon, 7 Sep, finds it in Simha and begins Bhadrapada.

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 Aug, with the Sun in Karka, began Shravana. This Shukla paksha reads Shravana 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 126.8° round the stars. Vikram Samvat numbers that year 2078; Shaka Samvat numbers it 1943.