Perihelion Day marks Earth's annual closest approach to the Sun in its elliptical orbit, occurring due to the planet's elliptical path around the Sun. Unlike a perfect circle, Earth's orbit is an ellipse, where the distance between Earth and the Sun varies throughout the year. Perihelion, derived from the Greek words 'peri' (around) and 'helios' (Sun), refers to the point in Earth's orbit nearest to the Sun.
As Earth orbits, its velocity changes. At aphelion, the farthest point from the Sun, the planet moves at its slowest pace due to gravitational influences. The Sun's pull then accelerates Earth as it starts its journey back toward perihelion, the closest point to the Sun. At this juncture, Earth moves at its maximum speed, overcoming the Sun's gravitational force to continue its path in space.
However, this cycle isn't an exact repetition due to gravitational interactions with other celestial bodies. Planetary movements, notably influenced by Jupiter and the Moon, cause deviations in Earth's orbit. Additionally, Milankovitch cycles introduce variations in Earth's orbit over longer periods, further affecting the timing of perihelion.
In 2024, Perihelion Day occurs on January 3, at 1 UTC (8 pm CDT on January 2), where Earth approaches the Sun approximately 3% closer than during its farthest point, aphelion, in early July. The difference in distance is striking, with about 3 million miles (5 million km) between perihelion and aphelion, whereas the average distance is approximately 93 million miles (150 million kilometers).
This close approach coincides with the northern hemisphere's winter season, highlighting that proximity to the Sun doesn't solely determine a region's temperature. Instead, factors like Earth's tilt and its alignment with the Sun during different seasons contribute to varying climate patterns.
Perihelion Day showcases the intricate dance between Earth and the Sun, revealing the dynamic interplay of gravitational forces and orbital mechanics that govern our planet's journey through the cosmos.
