It's interesting that in most countries the seasons are regarded as changing at the time of the Solstices. Here in Australia the first of march is officially the start of Autumn and the first of September is the start of Spring. Why? Well, when Sydney was a penal colony the British troops changed from Summer to Winter uniforms on the 1st of March and back to Summer uniforms on 1st September, so ever since we have kept those timings. (Yesterday in Sydney the temperature at mid day was about 86 degrees and overnight still about 70 so you can see how well that works.)