They are the result of the tilt of the Earth’s axis in relation to its path around the Sun. Our planet makes an angle of 23.5 degrees with the plane of its orbit – like a top that rotates tilted around another object, with its axis always pointing in the same direction. This angle means that, when it is summer in Brazil, for example, the Southern Hemisphere receives more sunlight than the Northern Hemisphere. “There, the days here are long and hot because the Sun hits the surface directly, almost perpendicularly”, says astronomer Rundsthen Vasques de Nader, from the Federal University of Rio de Janeiro (UFRJ). In winter, the situation is reversed: as the sun’s rays fall more inclined, the days are short and cold. Already at the arrival of autumn and spring, the amount of light and heat received by the two hemispheres is the same. It is worth remembering that the length of hours of sunshine in a season also varies according to latitude.
Therefore, the seasons of the year are well defined in the temperate regions of the globe and little in the tropics. Many people think that the variation in the distance between the Earth and the Sun also influences the seasons, but this is not true. “The distance between the closest and furthest point of the Earth’s orbit in relation to the Sun is negligible for this phenomenon”, says Rundsthen.
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The tilt of the Earth’s axis produces the four seasons.SUMMER IN THE SOUTHERN HEMISPHERE WINTER IN THE NORTHERN HEMISPHERE
The 23.5 degree inclination of the Earth’s axis causes the Southern Hemisphere to receive more sunlight than the Northern Hemisphere. The sun’s rays fall directly on the southern half of the Earth, which is warmer
SPRING IN THE SOUTHERN HEMISPHERE AUTUMN IN THE NORTHERN HEMISPHERE
Again, the Earth aligns with the sun. At the equinoxes, days and nights are 12 hours long in both the Northern and Southern Hemispheres.
WINTER IN THE SOUTHERN HEMISPHERE SUMMER IN THE NORTHERN HEMISPHERE
The situation is reversed: now it is the Northern Hemisphere that is most exposed to the sun’s rays. In the South, the time of clarity and heat decreases, because the sun’s rays arrive inclined to illuminate the surface
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AUTUMN IN THE SOUTHERN HEMISPHERE SPRING IN THE NORTHERN HEMISPHERE
At points where the Earth is opposite the Sun (the so-called equinoxes), the axis of inclination makes no difference. Both hemispheres receive the same amount of heat and light
Latitude makes a difference
Even in the same season, the day has different lengths in a tropical city and in another, with a temperate climate.