2043
Tuesday, 15 September 2043
In 2043 the nakshatra runs from 11:41 am on 15 Sep to 12:15 pm on 16 Sep. It covers part of the madhyahna on two days: 109 of its 148 minutes on 15 Sep and 74 of its 148 minutes on 16 Sep. By the rule, the day on which it covers more of that period is taken†: Tuesday, 15 September 2043. This year the nakshatra comes 2 times in the solar month; the rule takes the later†.
2044
Sunday, 4 September 2044
In 2044 the nakshatra runs from 9:08 am on 4 Sep to 11:31 am on 5 Sep. It covers the whole madhyahna (11:04 am–1:35 pm) on Sunday, 4 September 2044, but only 28 of its 151 minutes on 5 Sep, so that is the day of Onam.
How the date is fixed
Onam is the day of Shravana nakshatra in the solar month of Simha (while the Sun is in sidereal Simha); the lunar month does not enter. The date is the day whose madhyahna, the middle of the day (the third of five equal parts of the daytime) the nakshatra covers completely. If it covers only part of it on two days, the day on which it covers more of that period is taken†. If the nakshatra comes twice in that solar month, the later one is taken†.
† Practice varies between schools; our faculty is reviewing these rules.
About
Onam is fixed by nakshatra and by the Sun, not by tithi: the main day, Thiruvonam, is the day on which the Moon is in Shravana (Thiruvonam) nakshatra during the Malayalam solar month of Chingam, while the Sun is in sidereal Simha, in August or September. The lunar month does not enter, so the day can fall in Shravana or in Bhadrapada. The day on which the nakshatra holds the middle of the day (madhyahna) is taken, and when Thiruvonam comes twice in Chingam the later one is kept; Kerala's own almanacs occasionally print the next day. The ten days from Atham (Hasta) to Thiruvonam are the festival. It recalls the annual return of King Mahabali to his people.
How it is observed
Flower carpets (pookalam) for ten days, the Onam sadya feast on Thiruvonam, boat races and Kathakali.