Pradosha Vrata is observed on the 13th day of a fortnight and there are two Pradosham in a Hindu month. Lord Shiva and Goddess Parvati are worshipped in the evening during twilight on this day. In some regions, the day is dedicated to Nataraja form of Shiva. The fasting on this day is observed for success, peace and fulfillment of desires. It is said that mere darshan of any of the one form of Shiva removes ignorance.
Pradosham is observed when the Trayodashi Tithi is there during the twilight period. This is important.
The importance of Pradosha Vrata and how to observe it is narrated in the Skanda Purana.
There are two methods of fasting on the day. Some people observe a 24-hour fast which includes not sleeping during night. Another method is fasting from sunrise till sunset and after Shiva puja in the evening the fast is broken.
Pradosham is the twilight period just before sunset and after sunset. Pujas and prayers are performed during this period. Many people during this period spend the time in a Shiva temple or listening to the glory of Shiva.
In the evening, an hour before sunset the devotee takes bath and prayers are offered to Lord Shiva, Goddess Parvathi, Ganesha, Kartik and Nandi. After the initial prayers, Lord Shiva is worshipped in the form of a Kalasha (sacred pot). The Kalasha filled with water is covered with darbha grass and a lotus is drawn on the pot.
Another form of worship is the puja of Shivling. The shivling is bathed with water and Bilva leaves are offered. Some people use a painting or picture of Shiva for worship. It is said that offering Bilva leaves on Pradosham is highly auspicious.
After this people listen to the Pradosha Vrata Katha or story or read chapters from Shiva Purana. Then the Maha Mrityunjaya Mantra is recited 108 times.
After this the water used in the puja ceremony is given as ‘Prasad’ along with sacred ash. The ash is applied on the forehead.
It is said that just lighting a single lamp during Pradosham period is enough to please Lord Shiva and the act is highly rewarding. Majority of Shiva devotees have a darshan of Shiva during Pradosham in a nearby temple.