Every month on the 13th lunar day – 2 days(waning and waxing moon) Pradosha pooja is held. Special abishekam with Shri Rudra mantra parayanam is held during the Pooja.
Pradosh Vrat, which is also known as Pradosham in South India, is observed to seek blessings of Lord Shiva.
Pradosh Vrat is observed on both Trayodashi Tithis, i.e. Shukla Paksha Trayodashi and Krishna Paksha Trayodashi, in lunar month. Some people distinguish between Shukla and Krishna Paksha Pradosham.
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