Significance
Bhai Dooj, the fifth and final day of Diwali, celebrates the bond between brothers and sisters — much like Raksha Bandhan. Sisters apply a tika to their brothers and pray for their long life and prosperity.
It recalls Yama, the god of death, visiting his sister Yamuna, who welcomed him with a tilak; hence it is also called Yama Dwitiya.
Rituals
Sisters perform aarti, apply a ceremonial tika of roli and rice, and offer sweets to their brothers, who in turn give gifts and pledge protection. Families gather for a festive meal. Brothers who cannot visit are remembered in prayer.
How the date is fixed
Bhai Dooj falls on the Dwitiya of Kartika Shukla paksha, two days after Diwali; the tika is best applied in the auspicious afternoon window shown above.