Pradosh or Pradosh vrat is an auspicious Shiva Puja observed on every 13th day in both Paksha of a Hindu month. In August 2012, Pradosh vrat dates are: August 15 & 29 August. Both Pradosham pooja in August 2012 is Budh Pradosh as it falls on Wednesday (Budhvar).
Pradosh puja time for any pradosh vrat is 4.30 to 6’0 clock in the evening of Trayodasi tithi.
Guru Pradosh of 15 August 2012 falls in Krishna Paksha of Shravan month as per all chandramana or lunar calendars followed in Maharashtra, Gujarat, Karnataka & Andhra Pradesh.
Pradosh vrata of 29 August 2012 falls in Shukla Paksha of Bhadrapada month in North Indian Hindi calendars. It falls in Krishna Paksha of Shravana month as per Telugu, Kannada, Marathi & Gujarati calendars.
Here is the prayer to chant on Pradosh vrat – Pradosh Ashtakam