In the lunar Hindu calendar, Kartika begins with the new moon in November and is the eighth month of the year except in Gujarat, where it marks the new year that falls on Diwali. In the solar religious calendar used in Tamil Nadu, Kartikai begins with the Sun's entry into Scorpio and is the eighth month of the year.
In the Vaishnava calendar, Damodara governs this month.
Kārttikai (கார்த்திகை, /kɑːrt̪iɡəj/) is the eighth month of the Tamil calendar used in Tamil Nadu and northern and eastern parts of Sri Lanka. It corresponds to November/December in the Gregorian calendar. It begins when the sun enters the sign of Scorpio. Many festivals, such as Karthikai Deepam, are celebrated in this month. The name of the month is derived from a star, kārttikai (கார்த்திகை).
The festival of Kartik Poornima (15th day Full Moon) falls in this month, celebrated as Dev Deepavali in Varanasi. This coincides with the nirvana of the Jain Tirthankara - Mahavira and the birth of the Sikh Guru Nanak, Guru Nanak Jayanti. And also, the well known festival, for the god of Sabarimalai, Ayyappan's garland festival. This is also known as Tripuri Pournima.
The second day of first of Karthika, called Bharatrudwitiya, is celebrated with sisters entertaining their brothers, following the legend of Yamuna, who entertained her brother Yama on the same day.