The Earth has two main movements: rotation around its axis, with a period of 24 hours, creating day and night, and transition around the sun, with a period of 365 days, the Earth year. The Earth's axis of rotation is tilted in relation to the plane of its orbit around the sun, so that each hemisphere of the Earth, northern and southern, receives different amounts of solar radiation throughout the year, which causes the seasons of spring, summer, autumn and winter. At the beginning of spring, the spring equinox occurs, when the length of the day is equal to the length of the night and both hemispheres of the Earth receive the same amount of solar radiation.
As the Earth continues in its orbit around the sun, the days get longer and the nights get shorter until the summer solstice occurs, when the longest day and the shortest night of the year occur. After that, the days get shorter and the nights get longer until they become equal again at the autumn equinox. Then the nights increase in length and the days decrease until the winter solstice when the longest night and the shortest day of the year occur.
The tables below show the beginning of the seasons in both hemispheres. The 21st, mentioned as the beginning of the seasons, varies annually by one to two days due to the inclusion of a day (February 29) in leap years.
Seasons in the Southern Hemisphere:
September 21st | Early spring | Spring equinox |
December 21st | Early summer | Summer solstice |
March 21st | Early autumn | Autumn equinox |
June 21st | Beginning of winter | Winter Solstice |
Seasons in the Northern Hemisphere:
September 21st | Early autumn | Autumn equinox |
December 21st | Beginning of winter | Winter Solstice |
March 21st | Early spring | Spring equinox |
June 21st | Early summer | Summer solstice |
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