Shivaratri is great festival of convergence of Shiva and Shakti. Chaturdashi Tithi during Krishna Paksha is observed as Masik Shivaratri or Masa Shivaratri and staunch devotees of Lord Shiva observe fast and worship Shiva Linga on all Shivaratris in the year. In a year there are usually twelve Shivaratri days.
Shivaratri which falls during Shravana month is known as Sawan Shivaratri. As whole Shravana month is dedicated to perform Shiva Puja, Masa Shivaratri during Sawan month is considered highly auspicious. Sawan Shivaratri is more popular in North Indian states - Uttarakhand, Rajasthan, Uttar Pradesh, Madhya Pradesh, Punjab, Himachal Pradesh and Bihar where Purnimant Lunar Calendar is followed.
Vrat Vidhi – One day before Shivaratri Vratam, most likely on Trayodashi, devotees should eat only one time. On Shivaratri day, after finishing morning rituals devotees should take Sankalp(संकल्प) to observe full day fast on Shivaratri and to take food next day. During Sankalp devotees pledge for self-determination throughout the fasting period and seek blessing of Lord Shiva to finish the fast without any interference. Hindu fasts are strict and people pledge for self-determination and seek God blessing before starting them to finish them successfully.
On Shivaratri day devotees should take second bath in the evening before doing Shiva Puja or visiting temple. Shiva Puja should be done during night and devotees should break the fast next day after taking bath. Devotees should break the fast between sunrise and before the end of Chaturdashi Tithi to get maximum benefit of the Vrat. According to one contradictory opinion devotees should break the fast only when Chaturdashi Tithi gets over. But it is believed that both Shiva Puja and Parana (पारणा) i.e. breaking the fast should be done within Chaturdashi Tithi.
Shivaratri puja can be performed one time or four times during the night. The whole night duration can be divided into four to get four Prahar (प्रहर) to perform Shiva Puja four times.
Nishita Kaal Puja Time = 24:04+ to 24:48+
Duration = 0 Hours 43 Mins
On 13th, Sawan Shivaratri Parana Time = 05:52 to 15:42
Ratri First Prahar Puja Time = 18:59 to 21:43
Ratri Second Prahar Puja Time = 21:43 to 24:26+
Ratri Third Prahar Puja Time = 24:26+ to 27:09+
Ratri Fourth Prahar Puja Time = 27:09+ to 29:52+
Chaturdashi Tithi Begins = 17:40 on 12/Aug/2015
Chaturdashi Tithi Ends = 18:49 on 13/Aug/2015