The Earth has seasons due to the inclination of its rotation axis compared to its orbital plane around the Sun. This inclination causes variations in sunlight at different times of the year, thus causing the changes in seasons.
The Earth rotates on an axis that is not straight like a perfectly vertical top, but slightly tilted at about 23.5 degrees. It is because of this tilt that the Sun does not heat all regions evenly throughout the year. At times, the Northern Hemisphere is facing the Sun, receiving more direct light, thereby causing summer for us. Meanwhile, the Southern Hemisphere remains in shadow and experiences winter. Six months later, the opposite occurs: the Southern Hemisphere points toward the Sun while the North tilts into winter. Without this slight tilt, there would be no seasons!
The Earth revolves around the Sun in a slightly oval trajectory called an elliptical orbit, taking about 365 days and 6 hours to complete a full rotation. This small difference of 6 hours each year explains why we have a leap year every four years. As it travels along this orbit, the distance between the Earth and the Sun changes slightly throughout the year. However, it is not this variation in distance that creates the seasons, but rather the combination of our planet's orbital motion with the tilt of its axis. This tilt remains constant while the Earth orbits the Sun, and it is this unusual mix that causes the different levels of sunlight during various times, hence our seasons.
According to Earth's position around the Sun, each region receives varying amounts of solar energy. When the Northern Hemisphere tilts towards the Sun, it receives more direct and concentrated rays: this is summer in the north. At the same time, the Southern Hemisphere, tilted in the opposite direction, receives more diffuse, less intense rays, resulting in colder weather: this is winter. Six months later, the opposite occurs. What matters are not the differences in Earth-Sun distances, but the angle at which solar rays reach the surface. An angled ray of sunlight heats much less efficiently than a ray arriving directly. This is why the intensity of sunshine varies from season to season according to Earth's tilt.
The Earth, as it orbits around the Sun, experiences each year four key moments that mark the rhythm of the seasons: the solstices and the equinoxes.
The solstices are simply the moments of the year when the tilt of our planet brings maximum or minimum sunlight to a given hemisphere. Here in the northern hemisphere, around June 21, it's summer: a super long day, a very short night, and the Sun at its zenith is enough to warm us properly. Six months later, around December 21, everything is reversed: it's our winter, the longest night, and very little sunlight to warm us. Meanwhile, the southern hemisphere experiences exactly the opposite.
The equinoxes, around March 20 and September 23, are the days when both hemispheres receive the same amount of sunlight. On these dates, day and night last about 12 hours everywhere on Earth. It's the official transition between winter and spring, or between summer and autumn, depending on where you live.
The seasons directly impact the climate of each region according to its latitude and relief. When the tilt of the Earth modifies the amount of sunlight, some regions experience hot and dry summers, and mild and wet winters, like the Mediterranean climate. Other areas, like Siberia or Canada, endure strong variations with short and mild summers, and very long and decidedly freezing winters due to their high latitude. At the equator, on the other hand, seasonal variation is subtle, with temperatures remaining stable almost all year round, but with marked differences in precipitation: dry seasons and rainy seasons. In contrast, in temperate regions, each season clearly displays different landscapes, temperatures, and durations of sunlight, directly influencing local agriculture, as well as daily and cultural habits.
The equator is the only region on Earth where seasons are virtually nonexistent. Days and nights last about 12 hours year-round, and sunlight exposure hardly varies throughout the year.
The Earth is closest to the Sun at the beginning of January (at perihelion) and farthest away at the beginning of July (at aphelion). Surprisingly, these variations have very little direct impact on the seasons, which mainly depend on the tilt of the Earth's axis.
Around the Arctic or Antarctic Circle, there are periods lasting several weeks during which the Sun never fully sets (the midnight sun) or never fully rises (polar night). These phenomena are directly caused by the tilt of the Earth's axis.
The tilt of the Earth's rotation axis is currently about 23.5°, but this figure is not constant: it slowly oscillates between 22.1° and 24.5° over a period of approximately 41,000 years. This influences the intensity of the seasons on Earth in the very long term!
The seasons are inverted between the two hemispheres because the Earth is tilted on its axis. When the northern hemisphere is tilted toward the Sun and receives more direct light, it is summer, while the southern hemisphere is tilted away, which corresponds to winter, and vice versa.
The equinox corresponds to the moment when the Sun is exactly above the Earth's equator. As a result, the duration of day and night is nearly equal everywhere on Earth. This occurs twice a year, at the beginning of spring and at the beginning of autumn.
Equatorial regions receive a relatively constant solar intensity throughout the year. The angle of the sun's rays varies little, which means that there are no significant fluctuations in seasonal temperatures as seen at higher latitudes.
The areas near the poles, known as polar regions, experience periods during which the Sun does not set (the midnight sun phenomenon) or does not rise (polar night), due to the tilt of the Earth and their very high latitude.
No, the distance from the Earth to the Sun has very little direct impact on the seasons. The main cause is actually the tilt of the Earth's axis, which causes a variation in light intensity depending on the regions and the times of the year.
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