When does autumn really start?

Seasons are fundamental to how we understand the climate and the environment, but for hundreds of years academics have argued that their specialist field is the one which defines official start of autumn.

In meteorological terms autumn begins on September 1, as each season is defined as a three-month period.

Astronomers base the date of the seasons upon celestial events, in this case the autumnal equinox, when night and day are roughly equal length. The equinox will occur on Sunday, and normally takes places around September 21.

The third definition of the start of autumn, which is more fluid, comes from phenology – the study of periodic plant and animal life cycle events.

The start of autumn in this field is dictated not by a set date or a single event, but the changes in the natural world, such as the tinting of the trees and the ripening of autumn fruits.