The Earth's Climate

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The seasons

The Earth's trajectory around the Sun and the inclination of its axis of daily rotation in relation to its orbital plane (the ecliptic plane) generate seasonal weather and temperature variations.
In the course of the year, depending on the Earth's position in its orbit, a given point on the Earth's surface does not receive the same amount of solar radiation. The closer the Sun's rays are to perpendicular, the more heat they release. The more oblique their angle when they reach the Earth, the less heat they generate.

One year has:
- Two equinoxes: one around the 20th or 21st of March and the other around the 22nd or 23rd of September. At the equinox, the Sun's rays are vertical in relation to a point on the Equator. The durations of day and night are equal, hence the name equi-nox.
- Two solstices: one around the 20th or 21st of June and the other around the 21st or 22nd of December. At the solstice, the angle between the Earth's equatorial plane and the direction of the Sun's rays reaches its maximum. In the Northern Hemisphere the June solstice is the summer solstice, with the longest period of daylight in the year. In the Southern Hemisphere, the June solstice is the winter solstice.

In the temperate zones, in the middle latitudes, the astronomical seasons correspond to four phases in the year's climatic progression: winter, spring, summer and autumn. In the tropical regions the term "season" is also used, but in reference to a dry season and a rainy season.
The names of the seasons and the associated climatic phenomena are reversed in the two hemispheres — when it's summer in France, it's winter in New Zealand.