Pradosham Vratam is an auspicious day dedicated to Lord Shiva in a Hindu lunar month. In August 2015 Pradosham dates are August 11 and August 27. Another auspicious factor is that the first Pradosham is in the Hindi Calendar Shravan month dedicated to Lord Shiva.
Pradosham falls on the 13th day a Hindu lunar fortnight. There are two Pradoshams – one during the waxing phase of moon (Shukla Paksha) and another during the waning phase of moon (Krishna Paksha).
Fasting, special pujas and rituals dedicated to Lord Shiva and Parvati are observed on the day. Most pujas and rituals are performed during the twilight period (around 1.5 hours before sunset and 1 hour after sunset).
Fasting from sunrise to sunset is observed on anyone of the Pradoshams in a month. There are also many Shiva devotees who fast on all the Pradosham days.
You may also like to read