Onam, it is the annual Malayali harvest festival, in kerala of India this festival is celebrated at large scale. This festival is very famous in other states also because of its craze of celebration.
The keralas peoples do payattu, kalari named traditional dance to celebrate this. And the biggest boat race is also programmed on this day. This culture event is mostly of 9 to 10 days. On every day there is new celebration.
So tha main day for celebrating onam is 8th September and it is celebrated in 30 August to 8th September. So the onam os started.