The term "Pradosham" refers to the auspicious evening time that occurs one and a half hours before and after sunset, during which Lord Shiva and his vehicle Lord Nandi are worshipped. The Pradosham evening is observed on the 13th tithi (trayodashi) of both the waxing and waning lunar cycles, and is considered to be a significant religious occasion.
According to the legend, once Lord Indra was riding on his celestial white elephant, Airavata, and came across Sage Durvasa on the way. As a blessing, the sage offered Indra a special garland. Indra accepted the garland and put it on the head of Airavata. However, the flowers in the garland had a strong scent that attracted bees. Annoyed by the bees, Airavata threw the garland on the ground. Seeing this disrespectful act, Sage Durvasa became angry and cursed Indra and the rest of the devas, stripping them of their power, pride, fortune and everything else they had. As a result, they were defeated by the asuras in a battle led by King Bali.
After losing everything, Indra and the rest of the devas sought Lord Vishnu's help, who advised him that churning the celestial ocean was the only way to retrieve what they had lost. Indra then convinced the asuras to join them in this effort to obtain the nectar of immortality (Amrita). They used Mount Mandara as the churning rod and the serpent Vasuki from Lord Shiva's neck as the churning rope, with the asuras taking the side of serpent's mouth and the devas taking its tail. However, during the churning, the mount began to sink, prompting Lord Vishnu to take an avatar of a turtle, known as Lord Kurma, to support the mountain on his shell, allowing the churning to continue.
Due to the constant twists and pulls, the snake Vasuki began emitting deadly poison fumes, causing everyone to flee towards Lord Shiva for help. In an act of compassion, Lord Shiva swallowed the poison and saved them all. To celebrate this momentous event, Lord Shiva performed the cosmic dance (tandav) between the horns of his mount Lord Nandi, which was witnessed by Vishnu, Brahma and all the celestial sages. This divine moment of blessings from Lord Shiva is now known as "Pradosham," and is celebrated as an auspicious time for worshipping.
Five types of Pradosham
Nitya Pradosham (daily)
Paksha Pradosham (fortnight)
Maasa Pradosham (monthly)
Maha Pradosham (yearly)
Nitya Pradosham: It comes every evening roughly an hour and a half before and after sunset (around 4.30 pm to 7.30pm if we take 6pm as the average sunset time).
Paksha Pradosham: It comes on the 13th tithi (trayodashi) of the waxing lunar cycle.
Monthly Pradosham: It comes on the 13th tithi (trayodashi) of the waning lunar cycle.
Maha Pradosham: Trayodashi falling on a Saturday is referred to as Maha Pradosham. It is derived from the fact that the legend associated with Pradosham occurred on a Saturday (aka Shani Pradosham).
Pralaya Pradosham: Pralaya means “end”. In vedic puranas the term Pralaya is used to denote the ending of the final age when all living beings will look towards Lord Shiva to save them. This time is called Pralaya Pradosham.
The method of prayer, or pooja vidhi is as follows: Begin by taking a bath in the morning before sunrise and then worship Lord Nandi and Shiva by chanting their mantra 108 times. Start the fast (vrat) from then on and continue it till the end of the pooja at Pradosham time. In the evening, perform Shiva and Nandi pooja by lighting a diya and pouring milk over the Shivlingam and Nandi while chanting the mantra. You may also offer honey, sandalwood paste, curd, vibhuti (ash), Indian bael, rice, fruits, and other items, but milk is considered the most important as it symbolizes purity. Light an incense and chant the mantra 108 times once again. Finally, end the vrat after the pooja by eating the offerings.
Nandi Mantra: Om Namo Nandikeshwaraya Namah
Nandi Gayatri Mantra: Om Tatpurushaya Vidmahe Chakratundaya Dhimahi Tanno Nandih Prachodayat
You can also chant the "Maha Mrityunjaya Mantra" or "Om Namah Shivaya".