It's funny how stuff that's been in place since before you were born seems normal and generally passes without question, even when it's fundamentally absurd when you stop to think about it. I'm sure you can see where I'm going with this - this is basically how religion works. But that's not what I'm about here.
My concern here is: when does winter start? And, more generally, what are the dates of the seasons? Now obviously I'm taking a northern-hemisphere-temperate-zone-centric view of the world here, because, well, that's where I live, and some of the terms I'm going to be bandying about are only really relevant to that region. If you live at a similar latitude south of the equator you'll find your seasons are out of phase with ours by six months, whereas if you live near the equator you'll probably find significantly less year-round variation.
year-round variation in temperature, but that half the year was designated the "dry season" and the other half the "rainy season", the only difference between the two being that during the rainy season it would rain, torrentially, at 4pm every afternoon, regular as clockwork. One other interesting factoid from that link is that at Indonesia's latitude the difference between the longest and shortest days of the year (in terms of daylight, yes, I know they're 24 hours long everywhere) is a mere 48 minutes (it's about 6-8 hours in the temperate zones).
We're not really getting anywhere here; let's try and focus. When's the first day of winter? The winter solstice? Having December 21st (or thereabouts) as the first day of winter doesn't seem absurd, particularly when we in the UK are used to the coldest months typically being January and February anyway. But it seems somehow less sensible to have June 21st being the first day of summer; most of us would instinctively feel that it should be a bit earlier than that. And what of the convention of calling June 21st "Midsummer's Day"? Or of calling December 21st "Midwinter's Day", come to that? I don't think people would necessarily demand that it be smack dab in the middle of the season, but it being right at the start seems wrong.
So what to do? Well, one could adhere rigidly to the "midsummer"/"midwinter" thing and say, OK, the seasons are 365/4 = 91 days long (give or take the odd day) so we'll just go 45 days each side of the solstices and fill in the gaps from there. This gives you the seasonal dates as follows:
- Spring: 5th February to 6th May
- Summer: 6th May to 5th August
- Autumn: 6th August to 4th November
- Winter: 5th November to 4th February
- Spring: March, April, May
- Summer: June, July, August
- Autumn: September, October, November
- Winter: December, January, February
It's a useful indicator of personality type, though, to see how people respond to the notion that there is no answer - the more authoritarian types (small-c conservative, broadly speaking) get vaguely uncomfortable and annoyed that there isn't some central authority that will TELL THEM THE RUDDY ANSWER, on this topic as on many others where you just have to stick an arbitrary stake in the ground and no two people agree on where it should be: things like the age of consent, the safe weekly intake of alcohol, that sort of thing.
Bob Altemeyer's fascinating, very readable to non-academics, and freely downloadable (in PDF format) The Authoritarians is the canonical work of behavioural research on this topic. It doesn't say much about when winter starts, but, hey, nobody's perfect.