Scientific Meaning : Evening of the 13th phase of the moon, 90 minutes before and after Sun set. It is considered auspicious for worshipping Shiva in all Saivite temples - when thousands congregate for worship.
Importance of Pradhosam : Pradosha pooja is one of the most sacred and important among the poojas performed by Shivites to the Graceful Lord Shiva.
Shukla Paksha : 15 moon days from new moon to full moon.
Trayodasi : Thirteenth moon day.
Dhwadhasi : Twelfth moon day.
In Shukla Paksha and Krishna Paksha , the evening of the Trayodasi between 4.30 pm to 6.00 p.m. is called Pradosham. It comes once in fifteen moon days.Pradosha time is to pray Lord Shiva and invoke his Blessings. Praying in this time will free us from sins and gives Moksha - Hence the name Pradosha.
Story Behind the Pradhosam:
Once Dhevas and Asuras using the serpent Vasuki and the hill Mandhara were trying to get Amrutham (nectar) from the Khseerabthi (milk ocean). Then the terrible poison Halahalam came up. All got frightened and pleaded to Lord Shiva for rescue. Being the peak of mercy Lord Shiva ate that poison. Then as per His order they resumed their effort to get Amrutham. They got it on Dhwadhasi (twelfth moon day).
Without praying and thanking the God, by whom they got Amrutham, Devas started dancing and celebrating their victory. On Thrayodhasi (thirteenth moon day) they realized their sin of not praying the God and pleaded for forgiveness. The pleased graceful Lord Shiva forgave them and danced between the horns of the Nandhi (Holy Bull). That time is called Pradhosham.Whoever Prays Lord Shiva in that time, Lord Shiva fulfills their wishes and give them mukthi.
During Prodhosha time anointing (Abhishekam) the Shiva deity with the Following is considered fruitful. Oh Rudra, My salutations to your anger and to your arrows. My salutations to your bow and to your two hands. Rudra is always known to be easily pleased and through the praise contained in Sri Rudram, the fierce Rudra is calmed and becomes ready to grant us every conceivable blessing as requested in the Chamakam hymn.
During Prodhosha time Abhishekam with the Shiva deity.
Bhavaya Namaom Namah shiva