Every January, as the winter chill slowly begins to fade, many parts of India light up with colourful celebrations. Families clean their homes, prepare special sweets, and gather on rooftops to fly kites. It is the festival of Sankranti, celebrated under different names across the country. While it is filled with traditions, food, and joy, this festival is also closely linked to the movement of the Earth, the position of the Sun, and the science of seasons.
Sankranti marks the day when the Sun begins its northward journey across the sky. This movement is called Uttarayana. The word itself means ‘northern journey.’ In scientific terms, it refers to the time when the Sun appears to move from the southern hemisphere of the sky to the northern hemisphere. This happens because of the tilt of the Earth’s axis. The Earth does not rotate in a straight upright position. Instead, it is tilted at an angle of about 23.5 degrees. This tilt, along with its orbit around the Sun, causes the changing seasons and also influences how high or low the Sun appears in the sky throughout the year.
In December, during the winter solstice, the Sun appears at its lowest point in the sky for people living in the northern hemisphere. The days are shortest, and nights are longest. After this point, the Sun seems to climb higher each day. By around January 14 every year, the Sun enters the zodiac sign of Makara or Capricorn. That is why the festival is also called Makara Sankranti in many parts of India. The word 'Sankranti' itself means 'movement' or 'transmigration,' referring to the Sun's transition from one zodiac sign to another.
Unlike many Indian festivals that follow the lunar calendar and move around each year, Sankranti is one of the few that is based on the solar calendar. That is why it falls on or around the same date every January. This connection to the solar cycle also makes it a harvest festival. As the Sun begins to shine more directly over the Indian subcontinent, the days become longer and warmer. Crops such as rice, sugarcane, sesame, and pulses that were sown after the monsoons are now ready to be harvested. Farmers celebrate this moment of abundance and express gratitude for the harvest.
The foods prepared during Sankranti often reflect this connection to seasonal crops. In many regions, people make sweets using sesame seeds and jaggery. These ingredients are not chosen randomly. Sesame seeds are rich in oil and provide warmth to the body during winter. Jaggery is packed with minerals and energy. Together, they form a nutritious combination suited to the season. Scientific studies also show that such foods can help the body stay warm and healthy in cold weather.
Another unique feature of Sankranti celebrations is kite flying. While it is a joyful tradition, it also has interesting links to science. During this time of year, the Sun’s rays become slightly stronger after weeks of winter. Flying kites encourages people to spend time outdoors, exposed to sunlight. This helps the body produce vitamin D, which is essential for healthy bones and immune function. In earlier times, when vitamin supplements were not available, this was a fun and natural way for communities to soak up the Sun after long cold days.
In states like Tamil Nadu, Sankranti is celebrated as Pongal. The name comes from the act of boiling rice until it overflows from the pot. This too has symbolic meaning. The overflowing pot represents prosperity and abundance. Scientifically, Pongal occurs at the start of the Tamil month of Thai, which is seen as a period of hope and new beginnings. The alignment of the festival with the solar calendar means that it closely matches actual changes in the Sun’s position and temperature patterns, making it one of the most scientifically grounded festivals in India.
In Assam, it is called Magh Bihu, and in Punjab, it is celebrated as Lohri. Though customs vary, the underlying theme remains the same. These festivals welcome the Sun’s return to the north, the end of harsh winter days, and the arrival of a new agricultural season. They also highlight how closely traditional calendars and rituals were once tied to observations of the sky and nature.
Even today, scientists, farmers, and weather experts continue to monitor the solar cycle. Observing how the Earth tilts, rotates, and moves around the Sun is not just an ancient practice. It remains a key part of climate science, agriculture, and astronomy. Festivals like Sankranti remind us that long before telescopes and satellites were invented, people were already mapping the sky and designing their lives around the Sun.