When does it become Autumn?

The Autumnwatch (BBC) program asked this question during last week, I was having a think.

I think AutumnĀ  is that moment when you suddenly realise there’s a chill in the air, you haven’t got the right coat on, it smells like Winter is in the wind, and you look around and suddenly realise that although most of the trees are green, several are turning. (Then I stopped been philosophical, got excited, and bought DD and me a hat and gloves each! The week after the SEptember heatwave, with snow predicted for October?!)

IĀ love this time of year, I feel the most alive.

When do you think Autumn has begun – since it never reads the calender?