Panchang in Chahārbāgh, Alborz Province, Iran Sun 7 Oct 2018

Shiva’s worship centres on nishitha, the midnight muhurta. Chaturdashi runs from 12:02 on Sun 7 Oct to 09:32 on Mon 8 Oct, so only Sunday night’s nishitha (23:29–00:19 Mon) falls within it. No text giving Masik Shivratri’s time was found; nishitha is Tithika’s convention.

Masik Shivratri: every date in Chahārbāgh

The Moon gains on the Sun about 12° a day. Each 12° of lead is one tithi: 324°–336° is the 28th, Krishna Trayodashi. A day takes the tithi in force at its sunrise, 06:06 here. Dwadashi ended at 14:40 Sat, before it. Trayodashi ends at 12:02, when the lead reaches 336°. The lead passed 180° at the full moon of 25 Sep, so the Moon is waning: Krishna paksha.

The night of Sat 6 Oct ran from sunset 17:43 Sat to sunrise 06:06, 12 h 23 m. Cut into 15 muhurtas of 49 m, its 14th is Brahma Muhurta, the one before the last.

Daylight here, 06:06 to 17:42, splits into 8 choghadiyas of 1 h 27 m. Their names follow a fixed order that starts from the weekday, and each name is counted good, neutral or bad.

The night here, 17:42 to 06:07 Mon, splits into 8 choghadiyas of 1 h 33 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′. Purva Phalguni spans 133°20′–146°40′; the Moon entered its pada 3 at 140°. It leaves at 13:18, for Uttara Phalguni.

Add the Sun's and the Moon's places among the stars: 169.7° + 142.3° = 312°. The sum, cut into 27 parts of 13°20′, gives the yoga: 306°40′–320°00′ is the 24th, Shukla. It ends at 18:33, then Brahma.

A karana is half a tithi: 6° of the Moon's lead, so the first half of Trayodashi is Garaja and the second Vanija. Garaja ended at 01:21, when the lead reached 330°; Vanija runs until 12:02.

A Hindu day runs from one sunrise to the next, not midnight to midnight. This one runs 06:06 to 06:07 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: Simha gives Bhadrapada. The Sun enters Kanya on 17 Sep, inside the month. The next new moon, 9 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 9 Oct, with the Sun in Kanya, begins Ashwina. Until then this Krishna paksha reads Ashwina here, and Bhadrapada in the amanta count.

A samvat year begins with Chaitra, the month whose new moon finds the Sun in Meena: 17 Mar 2018, 16:41 Sat. Since then the Sun has moved 196.9° round the stars. Vikram Samvat numbers that year 2075; Shaka Samvat numbers it 1940.