Significance of Aadi Krithigai !!
Aadi Krithigai is celebrated on the Krithika star day of Aadi month and it is a day that is auspicious for Lord Muruga. Lord Muruga is the second son of Lord Shiva and Goddess Parvathi. Muruga in Tamil means beauty. In Sanskrit `Su’ means good-natured or beautiful. `Brahmanya’ means one who has realized Brahman. So, Lord Muruga is also known as Lord Subrahmanya.
As per Skanda Purana, Goddess Parvathi did penance and married Lord Shiva. The union of Shiva and Parvathi signifies the `Knowledge’ and `Grace’ coming together to deliver `Bliss’ in the form Lord Subrahmanya. When Devas pleaded Lord Shiva to put an end to the deeds of the demon Soorapadman, He took a form with six faces (i.e., Sathyojatham, Vamadevam, Thathpurusham, Eesanam, Aghoram, and Atho). Lord Muruga took birth from each of the 3rd eye of Lord Shiva as six sparks and formed a fireball. Agni and Vayu deva carried the fireball to the Vindhyas in the South (present Western Ghats). Even the fire God was unable to bear the heat of the fire and he dropped it in the water pond. When the hot fire touched the cold surface of the water, it speckled to 6 sparks, each taking the form of a beautiful baby boy in 6 six red Lotus flower. This waterbody is later known as Saravana Poigai. Six Kaarthigai Pengal (Nymphs) took care of the six babies still they attained boyhood. Then, Goddess Parvati embraced the six boys together they merged to one form named Lord Muruga with six faces and twelve hands. Hence Lord Muruga is also called Lord Shanmuga. In praise of the services rendered by the Karthigai Pengal, Lord Shiva and Goddess Parvathi granted them a boon that all special poojas for Lord Muruga will be held on Karthiga (Krithigai) nakshatra day.
This is the reason why the Krithigai star day is considered highly auspicious to worship Lord Muruga. And Aadi Krithigai is considered even more important because Aadi is the first month in the Dakshinayana Punyakalam (i.e) when the sun god changes his direction from the north towards south.