Today is the autumnal equinox
Equinox means equal night, and today, the 23rd of September, there will be equal amounts of darkness and daylight all over the World.
Actually, there will be more daylight than dark. We count daylight hours from the very first glimpse of the sun right until it vanishes completely at sunset whereas, at the equinox, it is the geometric centre of the sun that is above the horizon for exactly twelve hours. Also our atmosphere bends the light around the horizon even before the sun is visible.
From now, through until the vernal equinox on Friday 20th of March 2020, the days will be shorter than the nights.
When days becomes shorter than nights, deciduous trees signal to their leaves to stop producing chlorophyll, which is the green pigment essential for photosynthesis. In turn, this triggers the processes that change the leaves’ colour and lead to leaf-fall.
Because these processes are more dependent on the amount of daylight than they are on temperature, they take place at basically the same time every year despite our rapidly changing climate. The dominant colour of a year’s autumn leaves is their response to many factors, including temperature and drought, but the timing of their fall is governed by the solar system.
All photographs by DKG
Click below for more about leaf-fall: