Autumnal equinox, two moments in the year when the Sun is exactly above the Equator and day and night are of equal length; also, either of the two points in the sky where the ecliptic (the Sun’s annual pathway) and the celestial equator intersect. In the Northern Hemisphere, the autumnal equinox falls on September 23 2018, as the Sun crosses the celestial equator going south. In the Southern Hemisphere, the equinox occurs on March 20 or 21, when the Sun moves north across the celestial equator. According to the astronomical definition of the seasons, the autumnal equinox also marks the beginning of autumn, which lasts until the winter solstice (December 21 or 22 in the Northern Hemisphere, June 20 or 21 in the Southern Hemisphere). The concept of autumn in European languages is connected with the harvesting of crops; in many cultures autumn, like the other seasons, has been marked by rites and festivals revolving around the season’s importance in food production. Animals gather food in autumn in preparation for the coming winter, and those with fur often grow thicker coats. Many birds migrate toward the Equator to escape the falling temperatures. A common autumn phenomenon in the central and eastern United States and in Europe is Indian summer, a period of unseasonably warm weather that sometimes occurs in late October or November. Credit: Encyclopaedia Britannica.
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