On Thursday, July 3, 2025, Earth will pass aphelion — the point in its orbit furthest from the Sun. On this day, we will be 152.087 million kilometers away from the star. However, despite this “distance,” it has almost no effect on the Earth’s climate — and here’s why.
Axle tilt — the main driver of seasons
At first glance, it seems paradoxical that the Earth is furthest from the Sun in summer. During this period, it receives only about 93.55% of the solar radiation compared to what it receives in winter when it is at perihelion — the closest point to the Sun (147.1 million km). However, the main factor determining the change of seasons is the Earth’s axial tilt of 23.4°, not the distance to the Sun.
Axial tilt causes seasonal changes, as it determines which part of the planet receives more light during the year. Without this tilt, there would be no spring, summer, autumn, or winter, and days and nights would always last 12 hours. There would be eternal winter in the polar regions and constant summer with tropical rains at the equator. That is why this tilt angle is considered critical for the emergence and evolution of life on Earth.
Paradox of the Northern Hemisphere
Interesting fact: even though the Northern Hemisphere is farther from the Sun in the summer, it’s usually 2.3 °C warmer than the Southern Hemisphere during that time. The reason lies in geography: most of the landmass is concentrated in the north, and land heats up much faster than water. The oceans covering the Southern Hemisphere retain heat better, but accumulate it more slowly.
For comparison: on Mars, where the axial tilt is 25°, the impact of aphelion and perihelion is significantly more noticeable, since the planet’s orbit has a higher eccentricity (0.092). As a result, temperature differences between seasons on the Red Planet can reach 30 °C, which is an important factor when planning missions to Mars.
Not distance, but tilt
So, while aphelion is an interesting astronomical fact that truly affects the amount of sunlight reaching Earth, the key driver of seasonal change remains the tilt of the Earth’s axis. Our planet would be completely different without it.
Therefore, although aphelion and perihelion have a certain impact on the Earth’s climate, it is lost against the backdrop of the decisive role played by the Earth’s axial tilt. But with some other planets in the Solar System, the situation is different. Mars is a good example. Its axis has a similar inclination (25°), but the eccentricity of its orbit is much higher, at 0.092. And this is already having a significant impact on the climate of the Red Planet, making the change of seasons much more abrupt. Mars passes perihelion when it is summer in the Southern Hemisphere. As a result, summer temperatures in the south of the Red Planet can be as much as 30 °C higher than summer temperatures in the north. This circumstance has to be taken into account when planning space missions.
