Perihelion Day 2024: Earth Will Be At Its Closest To Sun In Entire Year On January 3. Know Why

Perihelion Day 2024: Earth will be at its closest to the Sun this year on January 3, at 6:08 am IST. When Earth is located at the point in its orbit closest to the Sun, the planet is said to be at perihelion. Every year, perihelion day falls around January 2 to 4, about two weeks after the December Solstice. 

Earth’s orbit also has a point which is the farthest from the Sun. This region is called the aphelion. 

Now, a question arises about why Earth’s orbit has its closest and farthest points from the Sun. The reason behind this is that Earth’s orbit around the Sun is elliptical. 

On January 3, 2024, Earth will be at a distance of 14,71,00,632 kilometres or almost 150 million kilometres from the Sun, according to timeanddate.com. 

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The word perihelion is derived from the ancient Greek words peri and helios, which mean close and Sun, respectively. 

Perihelion and aphelion are called apsides, which are defined as the points of shortest or longest distance of a celestial object in orbit around another astronomical wonder. 

Why is perihelion day not fixed?

The shape of Earth’s orbit around the Sun keeps changing due to the gravitational influences of other planetary objects, including the Moon. As a result, the Earth’s orbit around the Sun changes from nearly circular to elliptical every 100,000 years. 

Eccentricity defines the extent by which an elliptical shape differs from a perfect circle. A perfect circle has an eccentricity value of zero, while an ellipse has an eccentricity value between zero and one. 

The eccentricity value of Earth’s orbital path around the Sun keeps changing due to the gravitational forces exerted by different planetary bodies. As a result, perihelion day is not fixed. 

In 1246, the December Solstice and perihelion day coincided. Perihelion and aphelion dates have drifted by a day every 58 years since 1246. 

There is usually a difference of a day or two between the dates of perihelion days of two consecutive years. 

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About 4000 years later, in 6430, the perihelion will coincide with the March equinox, which is the beginning of astronomical spring in the Northern Hemisphere, and the beginning of astronomical autumn in the Southern Hemisphere. 

An equinox is one of the two times in the year when the Sun is exactly above the Earth’s equator, and day and night are of equal length. It is an event in which the planet’s subsolar point passes through its Earth’s equator. The subsolar point on a planet is the point at which the Sun is perceived to be directly overhead, and where the Sun’s rays strike the planet exactly perpendicular to the surface. 

Why are the Northern Hemisphere winter and the Southern Hemisphere summer the shortest seasons?

The Earth does not have seasons due to its changing distance from the Sun, but due to the planet’s tilt on its axis, which causes the hemispheres to receive sunlight differently at different times of the year. 

The December Solstice marks the beginning of astronomical winter in the Northern Hemisphere because this side of the Earth is tilted away from the Sun, while the Southern Hemisphere is tilted towards the Sun, causing that half to receive direct sunlight. As a result, the December Solstice marks the beginning of astronomical summer in the Southern Hemisphere. 

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At perihelion, the Earth moves at its fastest speed, which is 30.3 kilometres per second, according to EarthSky. Since the Earth moves at its fastest speed at perihelion, the Northern Hemisphere winter and the Southern Hemisphere summer are the shortest seasons. The Earth will quickly change its position in its orbit such that the Sun directly comes above the planet’s equator, resulting in the March equinox.