Autumn is the transition season between summer and winter, best noticed by the colour change in leaves and the harvest.
When is autumn?
Perhaps the most noticeable sign of autumn in the UK is the changing colours of the leaves. As a result of the falling temperatures in autumn, the chemical in the leaves that makes them green (chlorophyll) begins to break down while other chemicals (including Carotene) remain to give the leaves their yellow, red and brown colours.
The most vibrant displays of autumn leaves are evident when a dry summer is followed by an autumn with dry, sunny days and cold, but not freezing, nights.
Autumn according to the meteorological calendar begins in September and ends in November. In the astronomical calendar, the beginning of autumn is marked by the autumn equinox which occurs around the 22 September.
During the autumn equinox the sun shines directly on the equator and day and night around the globe are of almost equal length - a day and night of roughly 12 hours each.
Autumn has been significant in many cultures throughout history and even today many festivals and events around the globe occur around the autumn equinox, for example the Moon Festival in China or Michaelmas in the UK.
What is the weather like in autumn?
Autumn is normally associated with dropping temperatures and the nights drawing in as winter approaches. In the UK autumn can often bring unsettled weather and towards the latter part of the season can often bring stormy conditions with strong gales due to Atlantic depressions moving over the UK.
You can see what the weather has been like in the UK in autumns of the past on the Met Office's Climate summaries pages.