When is Astronomical Autumn in 2021? The date of the beginning of the astronomical autumn in the Northern Hemisphere has become known.
Astronomical autumn and autumnal equinox in 2021 in the Northern Hemisphere will come on September 22 at 22:21 Moscow time. This is stated on the website of the Moscow Planetarium.
With the arrival of the astronomical autumn in Russia there will be more and more cloudy days, and precipitation will acquire an areal character, Marina Makarova, chief specialist of the Hydrometeorological Center of Russia, told TASS.
What is Astronomical Autumn?
The movement of the Sun in the celestial sphere is determined by four points – the spring and autumn equinoxes and the summer and winter solstices. The period during which the Sun overcomes one of these sectors is called the season.
On September 22, 2021 at 22:21 Moscow time, the Sun, moving along the ecliptic (a large circle of the celestial sphere, along which the annual motion of the Sun relative to the stars visible from the Earth occurs), will cross the celestial equator and move from the Northern Hemisphere to the Southern Hemisphere. On this day, astronomical autumn will come in the Northern Hemisphere of the Earth, and spring will come in the Southern Hemisphere. Astronomers also call this day the day of the autumnal equinox.
On the day of the autumnal equinox, the Sun rises exactly in the east and sets in the west, spending exactly 12 hours above the horizon and 12 hours below the horizon, that is, day is equal to night.
After the autumnal equinox, the Sun will begin to rise south of the east, and set – south of the west. The length of daylight hours at the latitude of the capital will begin to decrease significantly and by the end of December it will lose five hours at once.
How will the weather change with the onset of the astronomical autumn?
With the arrival of the astronomical autumn, the warm half of the year is replaced by a cold one, Makarova recalled. “There are more cloudy days, the average daily temperature drops below 10 degrees, the plants stop growing, and chlorophyll is no longer formed in the leaves. That's it, nature is gradually falling asleep, ”she listed.
According to Marina Makarova, the onset of the astronomical autumn is also associated with a change in the nature of precipitation. They cease to be local, like in the summer.
Also, often with the arrival of the astronomical autumn comes the “golden” time of this time of the year. “The leaves begin to turn yellow, turn red, turn brown, then the leaf fall begins when the temperature is already below five degrees,” the forecaster noted.
