Pongal, a harvest festival, is celebrated here to thank the Sun God. Sun is regarded as the creator and sustainer of life on earth, and worshipping the Sun is an age-old practice still followed in India. We could find several hymns praising the Sun god in our scriptures and also several temples enshrining the Sun god (Surya) as the primary deity across India. Suryanaar temple is one of the Sun temples in south India (Kumbakonam, Tamilnadu) where wheat pongal is offered to the supreme deity, Sun God. So we can also prepare wheat pongal instead of rice pongal and offer to Sun God on this Pongal festival.
Aadi Perukku is a festival of fertility & prosperity being celebrated in South India for over 500 years. The 14th century Sangam Tamil literature, Paripadal, described the celebration of this festival elaborately. It gives us a glimpse of how our ancestors celebrated this festival and also how they revered the Mother Nature in those days. It is quite enthralling to read those old verses mentioning about the rivers passing through our neighbourhood. You may read those Sangam Tamil verses here.