Lord Skanda is son of God Shiva and Goddess Parvati and younger brother of Lord Ganesha. He 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.
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. Next Skanda Sashti after Soorasamharam is known as Subramanya Sashti which is also known as Kukke Subramanya Sashti and falls during lunar month Margashirsha. The following six temples, which are known as Arupadaiveedu are the most important shrines for Murugan devotees in Tamil Nadu, India.
Palani Murugan Temple (100 km south east of Coimbatore)
Swamimalai Murugan Temple (Near Kumbakonam)
Thiruthani Murugan Temple (84 km from Chennai)
Pazhamudircholai Murugan Temple (10 km north of Madurai)
Sri Subrahmanya Swami Devasthanam, Tiruchendur (40 km south of Thoothukudi)
Thirupparamkunram Murugan Temple (10 km south of Madurai)
Marudamalai Murugan Temple (a suburb of Coimbatore) is another important shrine.
Kukke Subramanya Temple, near Mangalore, Karnataka, India is also very famous shrine dedicated to Lord Murugan but it is not part of six abodes of Lord Murugan which are located in Tamil Nadu