Autumn is the season directly after summer when temperatures begin to fall. It comes before winter and is called "fall" in some countries, including the United States. It is known as a time of year when some trees start to shed their leaves.
In the Northern Hemisphere, autumn starts in the latter part end of September and runs until the latter part of December. In the Southern Hemisphere, it runs from March to June.
The first day of autumn is the autumnal equinox, which is a day in the year where daylight and nighttime are of an equal length. It ends on the year's shortest day, the winter solstice. As a result of this timing, days in the autumn are shorter than nights. While temperatures decrease during autumn in many parts of the world, in countries close to the equator, the difference is very slight.
Autumn is a time in many countries to harvest crops. It is also a time when birds begin their migration to warmer climates, and animals start collecting food to prepare for the winter. Some animals also start to grow thicker coats. It is also a time of year for annual cultural events, including Halloween and Thanksgiving.