GUWAHATI: Every year, June 21 marks the summer solstice in the northern hemisphere. This year, according to NASA, the summer solstice will globally occur on June 20 at 4:50 pm EDT, while in India, it will take place on June 21 at 8:09 pm IST.
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The Earth's rotation on its axis leads to the Northern Hemisphere receiving more direct sunlight between March and September. This results in summer for those living in the Northern Hemisphere because the Earth's axis is tilted about 23.5 degrees, causing the North Pole to lean towards the sun while the South Pole leans away. Consequently, when the North Pole is most directly pointed at the sun, reaching its highest point at solar noon for regions outside the tropics, we experience the longest daylight of the year. This phenomenon, occurring on June 20, 21, or 22, is known as the summer solstice, which translates to “sun stands still” in Latin.
Historically, around 200 BC, the Greek scholar Eratosthenes conducted an experiment to measure the Earth's circumference. He noted that on the summer solstice, sunlight shone directly down a well in Aswan, Egypt, indicating the sun was directly overhead. In contrast, in Alexandria, obelisks cast angled shadows, suggesting the sun was not directly overhead there. By calculating the difference in shadow lengths and the distance between the two cities, Eratosthenes provided an accurate estimate of the Earth's circumference and evidence of its spherical shape.
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Thus, the summer solstice signifies the longest day of the year when the sun reaches its highest point in the sky. Spiritually, it represents renewal, growth, and a connection to nature. Many cultures celebrate the solstice as the "middle of summer," honouring the sun's life-giving energy.