"Karthigai Deepam" is an ancient Tamil festival, celebrated on the full moon day in the Tamil month of "Karthigai", which falls between the months of November and December. In 2015, this festival was celebrated on 25th of November, which was a full moon day.
It is the Festival of Lights, where lamps made out of clay are lit in all households in Tamilnadu, a state in India. Also, this festival is associated with a miraculous natural phenomenon that happens year after year with accurate precision on this special full moon day.
Usually, the "Karthigai" month has not much wind blowing. But on this special day of full moon in "Karthigai" month (November - December), there will not be a bit of wind blowing anywhere across Tamilnadu.
Also, even though it is the month of heavy rains in Tamilnadu, on the day of the full moon in this month, there will not be a bit of rain anywhere across Tamilnadu.
This miraculous natural phenomenon gave the opportunity to keep clay oil lamps outside the house and let them burn whole night without them turning off. Of course, the oil has to be refilled and the wick has to be maintained properly. It is such a beautiful and miraculous sight to see so many lamps burning in open spaces in houses and temples across Tamilnadu.
Also, since ancient times, home made crackers made out of charcoal were used to be lit on this special day.
Ancient Tamils were awe struck by this natural phenomenon and understood the divinity of nature and the consistency of its laws. Hence, to respect nature and the force operating behind it with such precision and intelligence, they started celebrating the full moon day of Karthigai month as "Karthigai Deepam" festival.
To destroy this truth and to establish that they were superior, the Aryan invaders of India invented something called Diwali, called it the festival of lights, made it start on the first day of the month of "Karthigai" to supersede this awesome day of nature's miracle, burst crackers the same way as ancient Tamils did and created a fake story that a demon called Narakasura was killed by Krishna.