Panchang in Chahārbāgh, Alborz Province, Iran Mon 5 Sep 2016

Ganesha’s puja is done at madhyahna, the middle fifth of the day. Chaturthi runs from 17:54 on Sun 4 Sep to 20:09 on Mon 5 Sep, so only Monday’s madhyahna (11:48–14:21) falls within it.

Ganesh Chaturthi: every date in Chahārbāgh

The Moon gains on the Sun about 12° a day. Each 12° of lead is one tithi: 36°–48° is the 4th, Shukla Chaturthi. A day takes the tithi in force at its sunrise, 06:41 here. Tritiya ended at 17:54 Sun, before it. Chaturthi ends at 20:09, when the lead reaches 48°. The lead passed 0° at the new moon of 1 Sep, so the Moon is waxing: Shukla paksha.

The night of Sun 4 Sep ran from sunset 19:29 Sun to sunrise 06:41, 11 h 12 m. Cut into 15 muhurtas of 44 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 06:41 to 19:28, splits into 8 choghadiyas of 1 h 35 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 19:28 to 06:42 Tue, splits into 8 choghadiyas of 1 h 24 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 3 at 180°. It leaves at 18:39, for Swati.

Add the Sun's and the Moon's places among the stars: 138.9° + 180.7° = 319.6°. The sum, cut into 27 parts of 13°20′, gives the yoga: 306°40′–320°00′ is the 24th, Shukla. It ends at 07:27, then Brahma.

A karana is half a tithi: 6° of the Moon's lead, so the first half of Chaturthi is Vanija and the second Vishti. Vanija runs until 07:00, when the lead reaches 42°; Vishti until 20:09.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 06:41 to 06:42 Tue, so the hours after midnight still belong to Somawara.

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: Simha gives Bhadrapada. The Sun enters Kanya on 16 Sep, inside the month. The next new moon, 1 Oct, finds it in Kanya and begins Ashwina.

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 1 Sep, with the Sun in Simha, began Bhadrapada. This Shukla paksha reads Bhadrapada in both counts.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 7 Apr 2016, 15:53 Thu. Since then the Sun has moved 144.9° round the stars. Vikram Samvat numbers that year 2073; Shaka Samvat numbers it 1938.