Bhai Dooj is an ancient Hindu festival that comes two days after Diwali. In 2017, the date falls on Saturday, October 21. The festival is about the pious relationship between brothers and sisters.
The festival is marked by the ritual of Sisters' praying for the long lives of their brothers and to signify it they put a tilak on the forehead to keep the evil eyes of death, lord Yama.
There are several mythological accounts that narrate the history of Bhai dooj. By one account Lord of death Yama visited his sister Yami when she applied tilak and in return Yama gave her lots of gifts.
A pleased Yama said that those brothers who'll have the tilak on their foreheades will be fearless.
The best time to apply the tilak is between morning 7:50 and 9:15 AM and from 10:38 Am till 1:26 PM.
The time between 9:15 and 10:38 is not considered good as it will have the affects of Rahu (the severed head of demon Svarbhānu).