Skanda is a popular Hindu deity especially among Tamil Hindus. Lord Skanda is son of God Shiva andGoddess Parvati and younger brother of Lord Ganesha. God Skanda is also known as Murugan,Kartikeyan and Subramanyan.
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.
Skanda Sashti is also known as Kanda Shashti.
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. Also Sri Subrahmanya Swami Devasthanam, Tiruchendur temple in Tamil Nadu follows the same rule and Soora Samharam 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 monthKartika (which is during Solar month Aippasi) is the most significant one. Devotees observe six days fast which lasts on Soora Samharam day. Next day after Soora Samharam is known as Tiru Kalyanam.
Next Skanda Sashti after Soora Samharam is known as Subramanyan Sashti which is also known as Kukke Subramanyan Sashti and falls during lunar month Margashirsha.