Colorful Karthigai Deepam festival, India

Vaikom Mahadeva Temple,  mymanorama.manoramaonline.co

Thiruvannamalai temple, TN., India.crystalgrandeur.blogspot.com

Thiruvannamalai temple, TN., India.arunachalagrace.blogspot.com

Thiruvannamalai temple, TN., India.arunachalagrace.blogspot.com

Karthigai Deepam plus.google.com

If there is one religion that has the largest number of festivals, it is Hinduism and each festival  has an interesting legend that has  meaningful relevance in terms of moral  and  scientific values. Such festivals are joyous  preoccupations for the people and  are good for them psychologically. With respect to  temples, they enhance the continuity of spiritual values and promote devotion to God. In addition, the places of worship  wear festive look as a result of visit of lots of devotees on such occasions and they generate positive energy. 

Karthikai Deepam, the festival lights, is an important Hindu festival observed in most homes and 
temples. According to Tamil calender this festival comes in the month of Karthikai (mid-November to mid-December) when the moon is in union  with the constellation Karthigai (Pleiades) and pournami (full moon). This  cluster  of six stars in the firmament  has links with this  colorful festival.

Legend has it Lord Shiva created  six babies out of six sparks issued out of his third eye (eye of wisdom; in Tamil: Gnanakkan).  Six  celestial nymphs nurtured  them in the tank called Saravana. The Lord's consort Parvathi fused the six babies into one to form six faced Lord Kathikaya or Subramanyam (also Muruga). When he grew up, he   gained enormous power. Lord Shiva created Kathikaya (Muruga) to destroy Soorapadhman, a demon who was a menace to  sages, including Devas - celestial beings. Lord Shiva blessed the nymphs with immortality as they brought up the six babies  with care and affection and they became six stars (Pleiades) in the firmament, a lasting tribute to them for their services to the Almighty. Hence Lord Karthikaya (Muruga) has six abodes (temples; in Tamil : Aarupadai Veedu) in Tamil nadu.

Worshiping the six stars /karthigai nakshatram  is equal to worshiping Lord Subramanya. On the evening of this festival, women, wearing new dress light rows of oil lamps at homes and around the houses. In all Siva  and Murugan temples, this festival is observed with religious fervor, devotion and bakthi. Further, Karthigai deepam marks the birth day of Lord Karthikaya, the second son of Lord Shiva, first being Lord Ganesa.

In Indian mythology these six stars are considered as six celestial nymphs. One can find early reference to this festival in  Tamil work of poems 'Aganaanooru' that dates  back as far as Sangam Age (200 B.C. to 300 A.D.). This great work mentions the observance  of this festival on  the full moon day (pournami) of the month of Karthigai as per Tamil Calender. The festival  also finds reference in old Sangam literature like 'Akanaṉuṟu' and the poems of Auvaiyar. These references in  pretty old Tamil literature imply how the Indians, in particular, Tamils,  had a good knowledge of Astronomy centuries ago-long before major discoveries made by European Astronomers.

This festival  is widely celebrated in Tamil Nadu, in the neighboring state of Kerala, where it is known as 'Thirukarthika,' and in Andhra.  The lighting of  oil lamps at homes and temples is  a Hindu tradition and is considered as an  auspicious religious duty.  It is believed that it will  usher in peace and prosperity to the home and society. More over  the sanctity of the places is further purified. Yet another fact is lighting of oil lamps at home will guard the home dwellers from evil spirits, black magic and spells.
Ref:
https://en.wikipedia.org/wiki/Karthikai_Deepam