Overview
Kārtika, also written as Karttika or Kartik, is the eighth month of the Hindu lunar calendar and the Indian national calendar. The name of the month is derived from the position of the Moon near the Kṛttikā nakshatra on the full moon day. The month falls during the autumn season and corresponds to October–November in the Gregorian calendar.
In the Hindu solar calendar, Kartik corresponds to the month of Tula and begins with the Sun's entry into Libra. It is the seventh month in the Bengali calendar, where it is known as Kartik, and the seventh month in Vikram Samvat, called Kartika. In the Tamil calendar, it corresponds to Karthigai, the eighth month, which falls in the Gregorian months of November–December. In the Vaishnava calendar, it is observed as Damodara, the eighth month.
As with other months in the Hindu lunar calendar, Kartik has 29 or 30 days. Depending on the regional convention, the month begins on the day after Amavasya (new moon) in the amanta system or on the day after Purnima (full moon) in the purnimanta system. The month is divided into two fortnights of fifteen days each: Shukla Paksha, the bright half, and Krishna Paksha, the dark half. Each day in a fortnight is identified by a tithi, and the tithis repeat twice within the month across the two pakshas.
References
Adapted from the English Wikipedia article on Kartika (month).