Kaarthigai Deepam is celebrated on the full moon day in the Tamil month of Kaarthigai which coincides with Krithikai/Krittika Nakshatra in the month of November or December. The burning lamp with the divine flame is considered an auspicious symbol and believed to fend off evil forces and escort ecstasy and prosperity.It is also considered as the extension of the Deepavali festival and in some homes people double the number of lamps every day from the day of Deepavali and conclude with a number of lamps on the day of Kaarthigai Deepam or Deepam.
The month of Karthigai is of special importance as it is believed that Lord Muruga, the divine light of Lord Shiva, took his form during this month. Karthigai occurs on the day when the moon is in conjunction with the constellation Karthigai (Pleiades) and purnima. This constellation appears as a group of six stars in the firmament in the shape of a pendant from the ear. Many legends and lyrical poetry have grown round this star. The six stars are considered in Indian mythology as the six celestial nymphs who reared the six babies in the saravana tank which later were joined together to form the six faced Muruga. He is therefore called Karthikeya, the one brought up by the Karthigai nymphs.
It is believed that the Devas tried their best to have a full darshan of Lord Shiva and in the process Lord Brahma took the form of a swan and Lord Vishnu the form of a boar conducted an extensive search in the sky and in the neither world did they find him.Lord Shiva asked Lord Brahma and Lord Vishnu to determine the location of his head and his feet when he took a gigantic form. When they were unable to locate them, Lord Shiva took the form of a jyothi (flame)on the Thiruvannamalai hill whose ends could not be defined . Hence this festival is also known as Annamalai Deepam. Here, a special torch is lit on the top of the hill and is believed that Lord Shiva's jothi will be visible on this day. When the light on the top of the Tiruvannamalai Hill is unveiled on the Kartigai Deepam day, people see the big light and worship it. They recite again and again in a loud voice "Harohara". The esoteric meaning is that he who sees the light of lights that is burning eternally in the chambers of his heart through constant meditation attains immortality. The light on the Arunachala brings the message to you that the Self or Lord Shiva is self-effilgent, He is the light of lights.
According to another legend,it was on this day that Lord Muruga who first incarnated as six infants, out from six sparks from the third eye of Lord Siva, in Saravana Poigai (a holy tank, was conjoined into one, with the embrace of Goddess Parvati. Special poojas are performed to Lord Muruga on this day.
Karthigai Deepam is the oldest festivals celebrated in Tamil Nadu and Southern India, even before Deepavali and Navarathri celebrations. The reference of Karthigai Deepam can be found in many ancient Tamil literatures like ‘Ahananuru’ (200 B.C. to 300 A.D.) ‘Tolkappiyam' that dates back to 2,000 or 2,500 BC, 'Jeevakachintamani', an epic written by Jain poet, Thiruthakka Thevar, in the Sangam period, 'Karnarpadu', 'Kalavazhi Narpadu' dating around 1,000 BC and 'Pazhamozhi', even the famous poetess Avaiyyar, also mentions about the festival in her literary work.
The festival is celebrated for nine auspicious days with each day having its own special importance. There are special celebrations organized at Arunachaleswarar Temple amidst Annamalai Hills in Thiruvannamalai.People clean their homes and draw kolams (rangoli) and decorate it with lamps. The lamps(Agal) are placed in the pooja room and after Deeparathana the lamps are moved to different places in the house. The lamps glow in all homes in Tamilnadu on these days.It is a luminous sight to see little lamp arrayed on the extension, in front of the houses, in the courtyard were they are placed on Kolams (Rangolis), on windows, at the backyard etc. It is a beautiful sight in the villages, where houses are lined; little flames appear in an unending extension. The temples are all lit up and special prayers are offered. The observance of Karthigai Deepam festival, the festival of lamps, is believed to bring in fresh hope, peace, prosperity and happiness in one's life.This festival is also celebrated to commemorate the bonding between brothers and sisters in south India(analogous to Bhaiya-Dhuj and Raakhi). Sisters pray for the prosperity and success of their brothers and light lamps to mark the occasion.
The spiritual significance of celebrating Karthigai Deepam festival, is symbolised in the functioning of a lamp. The oil used to light the lamp, symbolises the innate tendencies in one, which, is responsible for the ego to thrive. The wick is the ego. The flame of the lamp symbolises, spiritual knowledge, which empties the oil, as it also burns the wick, the ego(body, mind complex). With the draining of the innate tendencies and the burning of the wick, one attains the spiritual goal, the realisation of the ultimate truth. Further the little flames of different lamps, symbolise the essence of universal oneness.