Astronomically, we say ‘farewell’ to Summer at the Autumnal Equinox, when the Sun passes over the equator - at 0750 UTC (0850 BST) on 23 September.
Autumn will now run until the Winter Solstice - 0419 UTC (~GMT) on 22 December. Then Winter will last until the Vernal Equinox, when the Sun passes back into the northern hemisphere - at 0349 UTC on 20 March 2020.
But in meteorological terms, Autumn is considered to be the months of September, October and November, with the other seasons following in 3-month periods.
And British Summer Time (BST) will cease at 0200 BST on 27 October, in compliance with an EU directive since 2002, which states that ‘Summer Time’ will be observed between the last Sundays in March and October, clocks to change at 0100 UTC.
UTC (Coordinated Universal Time) is the World’s civil time, having replaced GMT for the likes of international travel timing. UTC remains within 0.9 sec of GMT, both of which use leap seconds to ensure that the Sun passes over the Greenwich meridian at noon civil time to within 1 second.