Pradosh Vrat is a Hindu vrat which is dedicated to God Shiva and Goddess Parvati. This is also known as Pradosham. This is a bimonthly occasion on the thirteenth day of every fortnight in Hindu calendar. Pradosh Vrat is observed on both Trayodashi Tithis, i.e. Shukla Paksha Trayodashi and Krishna Paksha Trayodashi, in lunar month. The puja done on this day to helps reduce various problems such issues in marital life, weak health, obstacles in travel etc.
The word Padoshan is considered as an opportunity for the devotees to free himself from sins and remove negative karma.
"Pra" means remover and "Dosha" means malicious Karma. This Vrat varies from region to region because the duration of the Kaal varies from place to place.
When Pradosham day falls on Monday it is called Soma Pradosham, on Tuesday it is called Bhauma Pradosham and on Saturday it is called as Shani Pradosham.
Once, Devas and Asuras were churning the ocean to extract Amrit. King of snakes, Vasuki helped them to churn the ocean. Due to scratches on the body of Vasuki which was caused through churning, she emitted dangerous poison. Frightened by the appearance, devas and demons visited Lord Shiva for the help. To save the world from the poison, Lord Shiva swallowed it. He took the poison inside; Goddess Parvati choked his throat to stop the poison to get inflected in the body due to which his throat turned blue. After this, he got the name Neelkantha. As per philosophy, it is said that on 13th Hindu lunar day i.e. Trayodashi, Devas and Asuras understood that by not worshiping Lord Shiva they have committed a blunder. After realization, they requested Shiva to grant them forgiveness. Lord Shiva forgave them and then danced between Nandi's (celestial bull) horns. It is this time which is known as Pradosham. Worshiping Lord Shiva during this time, i.e. Pradosh Kaal results in the fulfilment of wishes, desires and wants
The fast commences after the bath before sunset. Lord Shiva, Goddess Parvati, Lord Ganesha and Nandi are worshipped. Milk and water is offered to the Shivlinga. Kalash is filled with water and Durva grass is placed over the Kalash. Over the grass, a lotus is drawn. Flowers, betel nuts, betel leaf, coin and rice are offered to the deity. Lord Shiva's Mantra 'Maha Mrityunjaya ' is also chanted 108 times and sacred ash is applied on the forehead. It is believed that lighting a single Diya (lamp) on Pradosham appeases the deity and yields highly fruitful results.