Pradosha pooja is one of the most important types of worship performed to Lord Shiva. The time between 4.30 and 6.00 in the evening of trayodashi (13th day of lunar fortnight) during both the shukla paksha (bright fortnight) and krishna paksha (dark fortnight) is known as pradosha. It occurs every fifteen lunar days. This pradosha time is especially meant for worshipping Lord Shiva. Offering prayers at this particular time rids us of our sins (hence the name pradosha) and grants final beatitude - moksha. During the pradosha time a special type of circumambulating called “soma sutra pradakshinam” is performed.

Pradhosha Purana:

Once the devas and asuras in quest of amrita (nectar), churned the kshirabdhi (ocean of milk) using the serpent, Vasuki, and the hill, Mandara. A terrible poison halahala came up which threatened existence. Frightened, they all sought refuge with Lord Shiva. The All-Merciful Lord Shiva consumed halahala. With His permission, they resumed their effort to obtain the amrita. The amrita appeared on a dwadashi (12th day of lunar fortnight). But, without paying obeisance to the God of Gods, without whom they would not have obtained the nectar, the devas started celebrating their victory.

On trayodashi (13th day of lunar fortnight) they realised their sin and pleaded for forgiveness. Pleased, Lord Shiva forgave them and danced between the horns of the divine Nandi (holy bull). This time came to be called pradosham. Whoever prays to Lord Shiva during this time, their wishes are fulfilled and are blessed with emancipation.

During pradosha time, anointing (abhisheka) of Shiva with the particular offerings bestows the following fruits –

Anoint the Lord with Love and He would give Himself!!

Bilvam and flowers can also be offered for Shiva pooja. Visit a Shiva temple on every pradosha to live under the shade of His grace blissfully. 

shivAya namaOm bhavAya namaH
bhavAya namaOm namaH shivAya

See Also:
1. Somasootra pradakshina
2. Pradhosha puja - in Tamil script
3. Pradhosham calendar for this year

4. பிரதோஷ மகத்துவம்