Seasons are caused by distance from the Sun
Earth's seasons are caused by the planet's 23.5-degree axial tilt, not by changes in its distance from the Sun. In fact, Earth is slightly closer to the Sun during Northern Hemisphere winter in January than during Northern Hemisphere summer in July.
What we know
Earth's axis of rotation is tilted approximately 23.5 degrees relative to the plane of its orbit around the Sun, a configuration that remains essentially fixed in orientation, pointing toward the same direction in space, as Earth completes its yearly orbit. Because of this fixed tilt, different points along Earth's orbital path place the Northern and Southern Hemispheres at different angles relative to incoming sunlight, and this changing angle, not changing distance, is what produces the seasons.
When the Northern Hemisphere is tilted toward the Sun, as it is during Northern Hemisphere summer, sunlight strikes that hemisphere at a more direct, higher angle, concentrating solar energy over a smaller surface area and producing longer daylight hours, both of which increase heating. When the Northern Hemisphere is tilted away from the Sun, during Northern Hemisphere winter, sunlight arrives at a shallower, more oblique angle, spreading the same amount of energy over a larger surface area and producing shorter days, both of which reduce heating. The Southern Hemisphere experiences the exact opposite pattern at the same time, which is precisely why the two hemispheres have opposite seasons: when it is summer in New York, it is winter in Sydney, despite both cities being the same distance from the Sun at that moment.
The distance explanation fails decisively on a straightforward empirical point: Earth's orbit is only mildly elliptical, and the planet actually reaches its closest approach to the Sun, called perihelion, in early January, during Northern Hemisphere winter, and its farthest point, called aphelion, in early July, during Northern Hemisphere summer. If distance from the Sun were the primary driver of seasonal temperature, the Northern Hemisphere should be warmest in January and coolest in July, the precise opposite of what is actually observed. The variation in Earth-Sun distance across the year, only about 3 percent between perihelion and aphelion, is also far too small in its effect on incoming solar energy, roughly a 6-7 percent difference in total solar irradiance, to explain the far larger seasonal temperature swings actually experienced at mid and high latitudes.
This orbital distance variation does have a small real effect, but it operates in the opposite direction from popular intuition and contributes to a documented, well-understood asymmetry: because Earth is closest to the Sun during Northern Hemisphere winter, Southern Hemisphere summers (occurring at the same time) tend to receive slightly more solar energy than Northern Hemisphere summers, and Southern Hemisphere winters tend to be slightly less severe in solar terms than Northern Hemisphere winters, though other factors, including the greater proportion of ocean versus land in the Southern Hemisphere, also strongly influence regional climate patterns and complicate simple comparisons.
The seasons-distance misconception is persistent partly because "closer means hotter" is an intuitively appealing analogy drawn from everyday experience, such as standing closer to a fire, and partly because most people never have direct reason to learn or verify the counterintuitive fact that Earth is actually closest to the Sun in the dead of Northern Hemisphere winter. NASA and planetary science educators consistently emphasize axial tilt as the correct explanation specifically because it accounts for observations that the distance explanation cannot, including the opposite timing of seasons in the two hemispheres and the persistence of clear, predictable seasonal patterns despite only minor changes in Earth-Sun distance across the year.
Common claims
- Seasons are caused by Earth's changing distance from the Sun.Not supported
- Seasons are caused by Earth's axial tilt.Accurate
- Earth is closest to the Sun during Northern Hemisphere winter.Accurate
- Both hemispheres experience summer at the same time.Not supported