Nag Panchami (Naga Panchami Puja, Nagula Panchami), is the festival of snakes observed in Shravan month. In 2013, Nag Panchami date is August 11, Sunday.
In 2012, Naga Panchami date was July 23, 2012 (Monday). Nag Chaturthi Upvaas 2012 was on July 22 (Sunday). Nag Panchami festival dedicated to Naga devatas (Serpent Gods), falls on the Shravan Shukla Panchami (fifth day in Shukla paksha during Sawan month).
On the day of Naga Panchami, nine prominent Serpent Gods (Nagas or snake Gods) are fed with milk and worshipped by certain rituals and pujas. Ananta, Vasuki, Padmanabha, Sesha, Kambala, Shankhapala, Dhruthrashtra, Takshaka and Kaliya are the nine prominent Serpent Gods.
Slokam to remember all the nine names of Naga Devatas:
Anantam Vasukim Sesham Padmanabham cha Kambalam
Shankhapalam Dhartarashtram Taxakam Kaliyam thatha
Etani navanamani cha mahatmanam
The sloka means – the above mentioned 9 Naga devatas are most auspicious and important serpent gods.
Legend of Naga Panchami:
Nag Panchami is celebrated all over India, but on different dates as mentioned above. Naga Panchami commemorates various legends and stories. One of these legends tells us about the victory of Lord Sri Krishna on Serpent Kaliya on the day of Shravan Shukla Panchami.
Nag Panchami is also celebrated as Garuda Panchami. On Naga Panchami day, people of North India and East India observe Ashtanag Puja. Ashtanag Puja is dedicated to Goddess Manasa, who is also called as the Queen of Serpents. Read Nag Panchami Puja Procedure (Naga Panchami Vrat Vidhi) here.