But that's just a convention. You're not explaining the phenomenon which gives rise to seasons or even what a season is. If some other culture decided to define equinoxes and solstices as the middle of a season then that would be another valid convention so to get to the root of the matter one has to define what a season is all about. The astronomical essence of seasons is the amount of daylight relative to darkness.

I don't really care about what causes it. The exact start and end dates of the seasons don't really matter, nor do they need to be consistent. Each season has things associated with them like fall has leafs turning orange and falling, or snow in winter.

Well now you're defining seasons in terms of weather and we all know how reliable that is. Here in London we've had zero snow this winter so far so does that mean we haven't had a winter? There are plenty of countries, especially the ones close to the equator, who have never experienced snow and whose summers and winters are barely distinguishable in terms of temperature yet they still have a summer and a winter defined by the longest and shortest day of the year.

>Here in London we've had zero snow this winter so far so does that mean we haven't had a winter?

If it didn't get colder than fall than it would be possible to skip winter.

So seasons are defined by temperature? In the UK we sometimes have our coldest weather in March. Does that mean the seasons have shifted? And what about countries close to the equator - do they have permanent summer? Seasons have nothing to do with temperature. Global warming is set to make that even more apparent.

>So seasons are defined by temperature?

In part. I'd say it's a combination of the temperature and amount of light you get per day.

The summer solstice around 20th June will always be mid-summer in the northern hemisphere even if it's freezing cold for the 45 days before and after. It's all about daylight and darkness. Nothing else.