Skanda is a popular Hindu deity especially among Tamil Hindus. Lord Skanda is son of God Shiva and Goddess Parvati. In south India, Skanda is considered as the younger brother of Lord Ganesha while in north India Skanda is considered as the elder brother of Lord Ganesha. God Skanda is also known as Murugan, Kartikeyan and Subramanya.
Sashti Tithi is dedicated to Lord Skanda. Devotees keep fast during Shukla Paksha Sashti day. For Skanda Sashti Vratam the day when Sashti Tithi is combined with Panchami Tithi is preferred. Hence Skanda Sashti Vratam might be observed on Panchami Tithi.
Notes: All timings are represented in 12-hour notation in local time of New Delhi, India with DST adjustment (if applicable). Hours which are past midnight are suffixed with next day date. In Panchang day starts and ends with sunrise.
When Panchami Tithi ends or Sashti Tithi starts between sunrise and sunset then both Panchami and Sashti are conjugated and this day is chosen for Skanda Sashti Vratam. This rule has been mentioned in Dharmasindhu and Nirnayasindhu. Many Murugan temples in Tamil Nadu, including famous Sri Subrahmanya Swami Devasthanam in Tiruchendur, follow the same rule and Soorasamharam day is observed one day before Sashti Tithi if on previous day Sashti Tithi is combined with Panchami Tithi.
Although all Sashti(s) are dedicated to Lord Murugan but Shukla Paksha Sashti during lunar month Kartika (which is during Solar month Aippasi or Karthikai) is the most significant one. Devotees observe six days fast which lasts on Soorasamharam day. Next day after Soorasamharam is known as Tiru Kalyanam.