Dhanteras or Dhanwantari Triodasi falls on the 13th day of the dark fortnight in the month of Kartik (October-November), i.e. two days before Diwali. The word ‘Dhan’ means wealth and ‘Teras’ means thirteen. Lord Yama is worshipped on this day to provide prosperity and well-being.
According to a legend, when the Gods and demons churned the ocean for Amrit or nectar, Dhanavantri (the physician of the Gods and an incarnation of Vishnu) emerged carrying a jar of Amrit or elixir. Both the Asuras and the Devas wanted the ambrosia, but finally Vishnu with a slight of hand managed to give the immortal nectar to the Gods and the Asuras were defeated. Thus the churning of the ocean resulted in the immortality of the Devas and was the reason for Goddess of Wealth, Lakshmi`s emergence.
Another legend says that on this day the 16-year old son of King Hima was doomed to die by a snake-bite on the fourth day of his marriage as per his horoscope.
On that fateful day, his young wife did not allow him to fall asleep. She laid all the ornaments and lots of gold and silver coins in a big heap at the entrance of her husband`s room and lighted innumerable lamps all over the place. And she went on telling stories and singing songs to him.
When Yama, the Lord of Death arrived in the guise of a serpent, he was blinded by the dazzle of gold ornaments due to which he could not enter the Prince`s chamber. So he climbed on top of the heap of the ornaments and coins and sat there whole night listening to the melodious songs. In the morning he quietly went away thus forgetting his purpose.
Thus the young wife saved her husband from the clutches of death. Since then this day of Dhanteras came to be known as the day of ‘Yamadeepdaan’. The lamps are kept burning throughout the night in reverential adoration to Yama, the God of Death.