There comes a time in the galactic dance of the planets when the Earth comes very close to the blazing embrace of the Sun. Every year, our planet reaches its closest point to the Sun in an elliptical orbit. This amazing event is known in meteorology as the day of perihelion. The point in the orbit of a planet or other astronomical body where it is closest to the Sun is called “perihelion”. The Greek word literally means “around the sun” (peri) or “helios”. The distance an orbiting body is from the Sun is called its “aphelion”. Let’s take a closer look at Perihelion Day, exploring its science, significance and the amazing dynamics that take place at this celestial meeting. (Also read: When is winter solstice in 2023? From date to Indian timings, know all about the shortest day of year )
What is Perihelion Day?
The orbit of any planet – not just the Earth – is not a perfect circle. In fact, it is an ellipse formed by the Earth’s gravitational pull from the Sun. (The Greek term for the sun is where the helion part of perihelion comes from). A planet’s orbital velocity decreases as it moves away from the Sun, as the Earth does. It travels at its slowest speed as it approaches ‘aphelion’, or the point furthest from the Sun. The planet is then pulled back by the force of the Sun. It accelerates as it begins to move back towards the Sun. It travels at maximum speed as it approaches the closest point to the Sun, or perihelion, fast enough to defy the Sun’s gravitational pull and continue its journey into space.
The planet’s orbit is eventually bent by the force of the Sun, causing it to fall back, and the cycle repeats itself. However, the process is never exactly repeated. A planet’s orbit can be disturbed by the gravitational pull of other planets, most notably Jupiter. In the case of the Earth, the Moon causes an extra wobble in the planet’s orbit. There are also variations in the Earth’s orbit over hundreds or even thousands of years, known as Milankovitch cycles. All this means that the date of perihelion varies from year to year.
When is Perihelion Day in 2024?
For 2024, our closest point will be at 1 UTC on 3 January (8 pm CDT on 2 January). Early January will see us approximately 3% closer to the Sun than early July, when we are at Earth’s aphelion, or furthest point, which is approximately 3 million miles (5 million km). In contrast, our average distance is approximately 150 million kilometers, or 93 million miles. Thus, during the first part of January, when winter is in the northern hemisphere, Earth comes closest to the Sun annually.