Manasa Devi is a Hindu cobra (serpent) Tantric Goddess, Queen of the Nagas. The story of her birth starts when Lord Shiva was sexually aroused on the banks of the Kalidaha pool, a pond in West Bengal in Rajnagar (a town). The Manasa's vahana (vehicle) is either the swan or snake. Swan is also a vahana of Saraswati. This connection gives her the same attribute - Wisdom and Knowledge. Snake symbolizes immortality. The Sij plant (Euphorbia Hguhria called Sehund or Sij in Hindi), of the cactus family, is sacred to her, as it can cure poisons. Naaga Kanya is the Buddhist form of Manasa.
Manasa is also known as a one-eyed goddess, because the Lord Shiva's wife was jealous of her and burned her two eyes. Shiva's children have three eyes and Manasa, with her one eye only, was sent down into the underground (Patala). In addition to Manasamangal Kavya, texts from the Brahma Vaivarta Purana are used in worshipping her. The said texts belong to Prakriti khanda (the second part of the Brahma Vaivarta Purana). This Purana is one of the 18 major Puranas and it is divided into four parts. It also deals with goddesses - Shaktis - the manifestations of Prakriti, the essential nature of intelligence. Prakriti khanda, the second part, celebrates the greatness of Durga, Lakshmi, Saraswati and Savitri during the creation of the world. During the Manasa puja ceremony people bath the statues of Manasa Devi with milk and recite the hymns taken from Prakriti khanda.
Nag Panchami is a snake festival for celebration of the Nagas (both deities and cobras). It takes place on the fifth day after Amavasya (dark moon) of the month of Shraavana (July/August). Nag Panchami is also the day of Manasa.
Manasa Devi has more names: Jagatkaru Priya, Jagat Gauri, Mansa Devi, Sidh Yogini, Padmavati, Naag Bhaamini, Shaivi, Jaratkaaru, Aastik Mata, Maha Gyaan Yuktaa, Naageshwari, Vish Haar, Monosha, Maa Monosha, and probably a few more.
Manasa is a folk goddess only because her worship reflects a caste conflict, as the orthodox Bhrahmanism deprived lower castes of the right to have access to Brahmanical learning. Manasamangal Kavya (a Bengali Hindu religious text) narrates a story about her and how she renewed her worship in Bengal. It was written sometimes around or after 13th Century AD.
Astika, an ancient Hindu Rishi (a sage), is the Manasa's son she
conceived with Jaratkaru, a mythological sage. The Jaratkaru's or
Astika's name therefore sometimes appear in variations of the Manasa's
name. Astika was a great sage that helped to prevent the genocide
of the Nagas, the ancient serpent people of India.