Kartik Purnima is celebrated on the full moon day of Kartik month every year. It is one of the most pious tithis of the year. As this month falls under Dakshinayana,hence it is considered as the most holy month to do sadhana and attain liberation from the worldly affairs. Lord Vishnu and Lord Shiva are worshipped on this auspicious day as it is believed that they descend on earth in the month of Kartik. It is also believed that Lord Vishnu, who goes to sleep on Ashadha Shuddha Ekadashi, wakes up on Kartika Shuddha Ekadashi.
Taking a holy dip in the river Ganga and lighting diyas in the evening are considered extremely auspicious on this day. According to legend, Lord Vishnu took the Matsya (fish) incarnation in the evening of Kartik Purnima. This is the reason why all kinds of donations and prayers done at this hour has a special significance. If the nakshatra of this day is Krittika nakshatra then it is known as ‘Mahakartiki’. In case it is Bharani, then it gives highly fruitful results and if it is Rohini, then the result is extraordinary.
A person who follows a ritual of bathing in the entire month of Kartik ends it on the day of Kartik Purnima. Many people observe the Satynarayana vrata and listen to the Satyanarayana katha on this day. Diyas are lit in all sacred places such as temples, near sacred fig tree and tulsi plants. Several diyas are lit by devotees and flown on the Ganga as a part of rituals. The sight of twinkling earthen lamps floating on the river lends a mystical touch to the celebrations. In Kashi, this tithi is celebrated as Devdeepavali-Mahotsava.
This day also marks the end of Chandraayan vrat. It is believed that all the wishes of a person are fulfilled who observes vrata from the day of Kartik Purnima and continues to do so on every full moon day. A huge number of people assemble to bathe in Ganga or any other holy river to wash off their sins and become free of all evils. Several fairs are organized on the banks of river Ganga on the occasion of Kartik Purnima. The Sikhs celebrate Gurunanak Jayanti on this day.