Michaelmas has been the name for 29th September since the eleventh century and falls on the cusp of late summer and early autumn.
Hwæt, we weorðiað wide geond eorðan
heahengles tiid on hærfeste,
Michaheles, swa þæt menigo wat,
fif nihtum ufor... emnihtes dæg.
Lo, we honour widely throughout the earth
the high-angel's tide in harvest,
Michael, as the multitude know,
five nights after the equinox day.
We are now slipping towards real autumn, cooler days and nights; lighting the stove and thinking about comfort food and warmer clothes.