Colorful Karthigai Deepam festival, India

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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