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Come January 4, and the Sun would look the largest it would ever be in the entire year. On this special day called Perihelion Day, earth will be the closest to the sun for the whole year. Perihelion is derived from Greek words peri (near) and helios (sun) aptly describing the event that happens every year between January 2-4.
Two weeks after the December solstice, the Earth reaches the closest to the Sun, or at the perihelion when it is winter in the Northern Hemisphere.On the other hand, the Sun will appear smallest at the time of reaching the aphelion point when the Earth is farthest away from the Sun. This happens two weeks after the June solstice, when there is summer in the Northern Hemisphere.
Can we notice the enlarged Sun on January 4?
Since the Sun’s apparent size changes very slightly, one may not notice any difference. While the Sun appears larger in the sky than at any other time of year, and the Earth would receive the most radiation from it, a 3% difference in the Earth’s distance from the Sun is hardly noticeable.
Earth doesn’t have a circular but oval-shaped orbit. It completes one revolution around this oval-shaped orbit every year, and reaches its closest point to the Sun around the same day. In 2025, this day falls on 4 January.
When will Perihelion occur?
(Image courtesy: NASA)
Perihelion will occur on January 4, 2025 around 8:28 EST in Washington DC, District of Columbia, USA, as per timeanddate.com.
Why earth’s orbit changes shape
The earth’s orbit has changed from being nearly-circular to oval-shaped due to the gravitational influences of other planetary objects, particularly the moon. According to timeanddate.com, every 100,000 years, the Earth’s orbital path changes from circular to elliptical. The difference of the Earth’s orbital shape from a perfect circle is known as its eccentricity. An eccentricity value of 0 is a circular orbit, while values between 0 and 1 describe an elliptical orbit.
However, Perihelion does not lead to hot temperature in Northern Hemisphere despite our planet’s proximity to the Sun. The seasons are set in motion by the axial tilt of Earth, not by how far the planet is from the sun.
When Perihelion takes place in the winter in the Northern Hemisphere, this region is tilted away from the Sun, resulting in cooler temperatures despite a slight increase in solar radiation.
(Images courtesy: iStock)
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