Autumn is one of the four meteorological and astronomical seasons is the season between summer and winter.
In the temperate zones, it is the time of harvest and falling leaves. In the autumn of the northern hemisphere, the sun appears to move from the equator to the southern tropic.
When is Autumn
Autumn starts astronomically here with the same day and night on September 22 or 23, meteorologically and biologically it is usually scheduled for early September. For the southern hemisphere, the astronomical beginning is on the 20th / 21st March.
Autumn ends astronomically on December 21 or 22 in the northern hemisphere and on June 21 in the southern hemisphere (winter solstice).
Linguistically, the word autumn has the same origin as the English word harvest (harvest), Latin carpere “pick” and Greek karpós “fruit, yield”, also Lithuanian kirpti “cut”, Greek krōpíon “sickle”. Originally, the word autumn meant “harvest time”.
Northern and Southern Hemisphere Autumn
Depending on whether autumn is in the southern or northern hemisphere, a distinction is made between southern autumn and northern autumn. Because of the migratory zenith of the sun between the southern and northern tropics, autumn is repeated in every hemisphere with an annual cycle. It is therefore also possible to deduce a northern spring from southern autumn and vice versa.
Seasonal schedule, an overview of the reference lines of the Earth’s orbit
Astronomically, it begins with the autumn equinox; (one also speaks of the Equinox or the day and night equation):
- in the Northern Hemisphere on September 22 or 23,
- in the southern hemisphere on March 20 or on the night of March 21,
and ends with the winter solstice (December 21 or 22 in the northern hemisphere, or June 21 in the south)
Since the Earth’s orbit around the sun deviates 1.7 percent from a circular orbit, the four seasons are not quite the same length. This also has an impact on the phenological beginning of autumn, which can differ from the astronomical climate. A distinction is also made between early autumn, full autumn and late autumn.
The months of September, October, and November in the northern hemisphere are approximated to autumn, and March, April, and May in the southern hemisphere.
In autumn, the leaves of the trees change color before they fall off. The cause is the slow withdrawal of the plant juices into the trunk or the roots. The chlorophyll is broken down and other leaf dyes provide the colorful coloring. These dyes are e.g. B. carotenoids and anthocyanins. Some of them are already present in the leaf, some are newly formed, for example with anthocyanins. The dyes have a protective function against sunlight so that the juices in the leaf can be transferred to the stem before it finally falls off.
In some countries around the world, autumn also changes the time from summer to normal time.