Today Karthigai Deepam festival is celebrated in Tamil Nadu and Andhra pradesh. The festival is very famous in Tiruvannamalai where the Deepam is lighted in the Arunachaleswarar temple and on the top of the Hill simultaneously around 6 pm on this day every year.
I give below a small write up on the festival:
Karthikai Deepam (Tamil: கார்த்திகை தீபம்) or Karthikai vilakkidu (Tamil:கார்த்திகைத் விளக்கீடு) [ also known as Karthika Deepam (కార్తీక దీపం) in Telugu ] is a Hindu specially Hindu Tamils and Hindu Telugu festival. The festival is observed in every home and every temple, and falls in the month of Kārttikai (mid-November to mid-December) as per Tamil calendar. This occurs on the day when the moon is in conjunction with the constellation Karthigai (Pleiades) and purnimai. 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. Houses and streets are lit up with rows of oil lamps (Deepam) in the evening of the festival day.
Lord Shiva appeared as an endless flame of light before Lord Vishnu and Lord Brahma, who each considered himself supreme and said that the matter could be tested if the two could search for Lord Shiva's Head and feet.
Lord Vishnu took the form of a boar(Sanskrit:Varaha, Tamil:Varahan) and delved deep into the earth, Lord Brahma that of a swan(Sanskrit:Hamsa, Tamil:Annam) and flew towards the skies. Lord Vishnu failed in his search and returned. But Lord Brahma, chancing upon a piece of Thazhambu, a flower, learnt from it that it had been floating down for thirty thousand years from Lord Shiva's head. He seized upon this and claimed to Lord Shiva that he had seen the other's top. Lord Siva realized the falsehood and pronounced that there would never be a temple for Lord Brahma in this world. He also interdicted the use of the flower Thazhambu in his worship. Lord Shiva appeared as a flame, this day is called Maha Deepam.
Rows of Agal vilakkus (oil lit lamps) are lit in every house. Karthigai is essentially a festival of lamps. The lighted lamp is considered an auspicious symbol. It is believed to ward off evil forces and usher in prosperity and joy. While the lighted lamp is important for all Hindu rituals and festivals, it is indispensable for Karthigai.
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.
In Telugu households, Kaartheeka maasam (month) is considered very auspicious. The Kartheeka month starts on the day of Deepawali. From that day till the end of the month, oil lamps are lit every day. On Kartheeka Pournami (full moon of Kartheeka month) oil lamp with 365 wicks, prepared at home, are lit in Lord Shiva temples. Apart from that, Kaartheeka puranam is read and fasting is observed till sunset, every day for the whole month.
Celebrations at Tiruvannamalai
Arunachaleswarar temple and Hill in Tiruvannamalai
Karthigai festival in Tiruvannamalai hills is very famous. On Karthigai day, a huge fire lamp is lit up on the hill, visible for several kilometers around the hill.
The fire (dheepam) is called Mahadeepam, as Hindu devotees visit the place, to pray and offer lord Shiva.