The Earth’s journey around the sun isn’t a perfect circle but rather a subtle ellipse, a slightly elongated oval. This elliptical orbit brings our planet to its closest point to the sun, known as perihelion, typically around January 3rd or 4th each year. The term “perihelion,” derived from the Greek words “peri” (near) and “helios” (sun), signifies this close solar encounter. In 2025, perihelion occurred on January 4th, placing Earth approximately 147 million kilometers (91 million miles) from the sun. This proximity might conjure images of balmy weather, but for those in the Northern Hemisphere, the reality is quite the opposite: a landscape often gripped by winter’s chill. This seeming paradox arises from a fundamental aspect of Earth’s celestial mechanics: the tilt of its axis.
While the Earth’s distance from the sun does vary throughout the year, the primary driver of seasonal temperature changes is the axial tilt. The Earth’s axis, an imaginary line running through the planet from the North Pole to the South Pole, is tilted at an angle of approximately 23.5 degrees relative to its orbital plane. This tilt dictates which hemisphere receives more direct sunlight at different times of the year. During the Northern Hemisphere’s winter, the Earth’s axis is tilted away from the sun. This means that sunlight strikes the Northern Hemisphere at a more oblique angle, spreading the same amount of solar energy over a larger area and leading to lower temperatures. Conversely, the Southern Hemisphere is tilted towards the sun during this period, experiencing the direct rays of the sun and consequently, summer’s warmth.
Perihelion, therefore, does not herald a global heatwave. While the Earth receives approximately 7% more sunlight at perihelion than at aphelion (its farthest point from the sun), the effect of this increased solar radiation is offset by the Earth’s axial tilt. The Northern Hemisphere, tilted away from the sun, experiences winter despite the closer proximity to the sun. The Southern Hemisphere, on the other hand, basks in summer, enjoying the combined effect of direct sunlight and the Earth’s closer proximity to the sun. The difference in landmass distribution between the two hemispheres also plays a role. The Southern Hemisphere has a significantly larger proportion of ocean surface compared to the Northern Hemisphere. Water, having a higher heat capacity than land, absorbs and distributes the increased solar radiation without a proportionally large increase in temperature.
The Earth’s elliptical orbit and the resulting variation in solar radiation are not unique to our planet. Johannes Kepler, a German mathematician of the 17th century, formulated the laws of planetary motion, revealing that all planets orbit their stars in elliptical paths. Each planet experiences its own perihelion and aphelion as it traverses its orbital ellipse. The degree of ellipticity, however, varies from planet to planet, influencing the difference in solar radiation received at these two points in their orbits.
The elliptical nature of Earth’s orbit leads to a slightly stronger gravitational pull from the sun at perihelion compared to aphelion. This difference in gravitational force, while subtle, affects the Earth’s orbital speed. According to Kepler’s second law of planetary motion, a planet moves faster in its orbit when it is closer to its star and slower when it is farther away. Consequently, the Earth travels slightly faster in its orbit during perihelion and slower during aphelion. This variation in orbital speed, coupled with the Earth’s axial tilt, contributes to the uneven distribution of sunlight and the resulting seasonal changes.
Beyond the Earth’s annual journey around the sun, the sun itself undergoes cyclical changes in activity. The solar cycle, spanning approximately 11 years, sees the sun transition between periods of relative quiescence and heightened activity known as solar maximum. During solar maximum, the sun exhibits increased sunspot activity, solar flares, and coronal mass ejections, which release vast amounts of energy and radiation into space. This increased solar output does have a measurable effect on the Earth, though not as dramatic as one might imagine. The total solar irradiance, the amount of solar energy reaching Earth, increases by about 0.1% during solar maximum. While this increase is relatively small, it can still influence Earth’s climate system over time, though the extent of its impact is an ongoing area of research.
It’s important to distinguish between the effects of perihelion and solar maximum. Perihelion is a fixed point in Earth’s orbit, occurring annually when the Earth is closest to the sun. Solar maximum, on the other hand, is a phase in the sun’s activity cycle, occurring roughly every 11 years. While both events involve changes in solar radiation reaching Earth, their timescales and underlying mechanisms are distinct. Perihelion is a consequence of Earth’s elliptical orbit, while solar maximum is a result of internal processes within the sun. The combined influence of these factors, along with the Earth’s axial tilt, shapes the complex tapestry of Earth’s climate and seasonal variations. So, while the Earth’s proximity to the sun during perihelion might seem counterintuitive to the winter chill experienced in the Northern Hemisphere, the interplay of orbital mechanics and axial tilt provides a clear explanation for this apparent paradox. Ultimately, the tilt of Earth’s axis reigns supreme in determining the seasons, overriding the relatively minor influence of the Earth’s varying distance from the sun.
