Seasons occur as a natural consequence of Earth’s axial tilt relative to its orbital plane, in combination with its revolution around the Sun. Earth’s moderate, 23.45 tilt accounts for the existence of the four seasons: spring, summer, autumn and winter.
The common misconception that seasons are a result of the Earth moving away or closer to the Sun can be easily refuted, considering the fact that the distance between the Earth and the Sun varies very little throughout the year. Furthermore, if this were true, the same seasons would occur at the same time in both hemispheres, which is obviously not the case.
The appearance of seasons is a result of the seamless, unique relationship between Earth’s axial tilt and its revolution. While the Earth is yearly revolving around the Sun, it alternatively exposes more of one side or the other to the Sun. Because the Sun is what provides us with heat, light and energy, the different amounts of sunlight that reach Earth’s hemispheres cause differences in climate that our ancestors have identified as seasons. This is also why, at any given time, the Northern and Southern hemispheres will experience opposite seasons.
The two solstices and two equinoxes are key dates in a year, when Earth’s axis passes through important positions on its orbit. The solstices mark the times when the poles are at their closest or furthest away from the Sun, having winter and summer as a result. During the equinoxes, the Sun’s rays appear to fall directly on the Equator, causing the beginning of fall or spring.
The vernal equinox (21st of March) marks the beginning of spring for the Northern hemisphere and autumn for the Southern one. On both hemispheres, the day is equal in duration to the night.
The autumnal equinox (21st of September) represents the beginning of autumn for the Northern hemisphere.
The summer solstice (21st of June) marks the onset of summer for the Northern hemisphere and winter for the Southern one. Up to this particular date, the days are longer than the night, reaching a maximum and then gradually starting to shorten, as the Sun begins to move south.
The winter solstice (21st of December) represents the onset of winter for the Northern hemisphere. It is the shortest day for the Northern hemisphere and the longest one in the opposite one.
In the temperate areas, the seasons cycle in the pattern presented above, however, things are different in the hot and the cold regions.
At the poles, there are only two seasons: Polar Day (spring and summer) and Polar Night (autumn and winter). Because the Sun’s light hits at a very steep angle, only a small amount of heat can reach the poles, thus accounting for the cold climate. As a consequence of Earth’s revolution and axial tilt, the poles are alternatively exposed to sunlight for half a year each: while the North Pole is exposed, the South Pole is in complete darkness and vice versa.
At the Equator, the hot regions are defined by two seasons: the rainy and the dry season. The tropical and subtropical regions are always exposed to direct sunlight because the Sun’s rays fall perpendicularly on the Equator.
Other factors also influence the seasons, such as: geographical position, proximity to oceans, the presence of currents etc. Our planet’s climate is a complex system in which all the elements are closely linked together.
