Onam is the great festival of Kerala and of Malayali communities everywhere. It is a harvest festival and a homecoming, and its main day is called Thiruvonam. The day is not fixed by a tithi like most Hindu festivals. It is fixed by a nakshatra, a lunar mansion, and by a solar month, which makes it one of the few festivals whose date follows two different clocks at once.
The legend
The tradition tells of Mahabali, an asura king of great generosity, whose reign was so just that the people lived in plenty and contentment. The gods grew uneasy about his power. Vishnu came as Vamana, a small Brahmin boy, and asked Mahabali for as much land as he could cover in three steps. Mahabali agreed, though his teacher warned him. Vamana grew until he covered the earth with one step and the sky with the next, and for the third Mahabali offered his own head. Pleased by his devotion, Vishnu granted that he might return once a year to see his people. Onam is said to be that visit. The story is told in the Puranas and the details vary, and many Malayalis enjoy the festival for its warmth rather than for any one version of the tale.
The ten days
The celebrations begin on Atham, the day of the Hasta nakshatra, and run for ten days to Thiruvonam. Each morning a pookalam, a floral carpet, is laid in the courtyard, growing larger and more intricate day by day. On the days before Thiruvonam, families buy new clothes (Onakkodi), swings are hung from trees, and in towns there are folk dances such as Thiruvathira Kali and the tiger dance of Thrissur called Pulikali. Boat races on the backwaters, including the snake boat races, are held around the festival, though not always on Thiruvonam itself.
Thiruvonam day
On Thiruvonam the family bathes, dresses in the traditional off-white and gold cotton of Kerala, and prays. The Onasadya, a vegetarian feast served on a banana leaf, often has more than twenty dishes, including rice, sambar, parippu with ghee, avial, thoran, pachadi, pickles, banana chips, and the sweet payasam. Elders give gifts, and in many homes the day ends with games and music.
How the date is fixed
The Moon takes about 27 days to pass through the 27 nakshatras. Thiruvonam is the Sanskrit Shravana, the twenty-second. The festival belongs to the Malayalam month of Chingam, the solar month in which the Sun is in Simha, from about mid August to mid September. The day used here is the civil day on which the Moon is in Thiruvonam at local solar noon, in Chingam. The table shows, for each city, the date and the hours the nakshatra begins and ends.
In a few years the Moon is in Thiruvonam twice before the Sun leaves Simha. We then take the later one, and a day on or after the civil day of the Sun’s entry into Kanya is outside Chingam. This rule was chosen because it agrees with the dates Drik Panchang lists for 25 city and year pairs, including one with two candidates. It is an astronomical rule that Kerala’s own almanacs and the government announcement may not follow in every year, and if the Kerala calendar you follow names a different day, use that.
Why cities differ
The nakshatra begins and ends at the same instant everywhere, but noon is at a different clock time in each city. A nakshatra that runs from the night before into the afternoon may include noon in one city and miss it in another. In those cities Onam is a day apart. The any-city tool works out the same day for other places, and Vishu is the other main festival of the Malayalam year.
A calm note
Onam is a festival of generosity and shared meals more than of precise hours. A pookalam on a doorstep and a meal with family, or with neighbours, honours the day wherever you live. Follow your own family and community for the day.