Spring Equinox: Indian temple where sun peeks through 5 windows every 5 minutes twice a year

March 20 is the Spring Equinox, and the Sree Padmanabhaswamy Temple in Thiruvananthapuram is the place where you can witness an extraordinary solar alignment on this day. The solar equinox occurs twice a year - in March and September. On this day, the sun appears directly over the equator since Earth’s axis is tilted neither towards nor away from the Sun. Sree Padmanabhaswamy Temple is an 8th-century shrine dedicated to Lord Vishnu. Its Gopuram, or the monumental entrance tower, is nearly 100 feet tall and is divided into seven tiers. There are five windows, and on the day of the equinox, the sun peaks exactly through them in an interval of five minutes. This astonishing occurrence is made possible because of the way the tower has been built. The windows are perfectly aligned on an East-West axis, making the temple one of the most well-known examples of ancient Indian archaeoastronomy.

Engineering precision at Sree Padmanabhaswamy Temple

At sunset, the temple's construction creates a visual spectacle. The Earth's axis is not tilted at the equinox, so the sun sets exactly west. It appears exactly in the centre of the topmost window. After 5 minutes, the Sun can then be seen through the window below the top one. Remember, the Earth is rotating, yet the sun appears to be descending in a straight line when seen through the windows of the temple tower. This repeats till it reaches the horizon, when it appears through the lowest window. This is a marvellous occurrence since ancient architects built the temple without modern surveying tools. The Sun is only partially visible on the day before and the day after the equinox because of the depth of the windows and the thickness of the walls.

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Significance of the sun peeking through the tower windows

It is an engineering marvel since the builders were able to achieve such precision as to ensure that the sun fully peaks through on just two days of the year. The architects had to calculate the exact latitude of Thiruvananthapuram to ensure that the orientation was perfect for the sun's path only on the equinox. The purpose of constructing the Gopuram tower in this way served a bigger purpose. When the Sun made this spectacular appearance on these two days, they became checkpoints that told the priests that it was the equinox and the seasons would change from then on. It is also symbolic of the transition of time and the omnipresence of Lord Padmanabha (Vishnu).