The seasons were originally set by the weather patterns. In parts of the world at mid-latitude (i.e. not near the equator or the poles), summer, spring, autumn and winter are fairly obvious. (Summer = hottest quarter. Winter = coldest quarter. Spring = when things start to grow. Autumn = when plants start to die.) As time has passed, it has become important to set a standard for when these periods begin and end; it is no longer reasonable to say that spring begins when the first tulip comes into flower. Although you can if you really like.
Today, one popular way for the choosing the seasons’ dates derives directly from the traditional weather patterns and is called the ‘modern meteorological reckoning’: in the Northern hemisphere spring beings on 1st March, summer on 1st June, autumn on 1st September and winter on 1st June. The seasons are reversed in the Southern hemisphere.
The most widely accepted system of splitting the year into four is by the ‘astronomical reckoning system’. This is based on the solstices (the longest and shortest days of the year) and the equinoxes (the two days of the year with equal daylight and night). The exact dates for these vary each year although they are usually around March 21 for the spring equinox, June 21 for summer solstice, September 21 for autumn equinox and December 21 for winter equinox. The astronomical reckoning is neat and tidy because it is based on something physical (the Earth’s given position in its orbit around the sun). Personally, I think these dates are a bit depressing: I’d rather not think of summer as starting at the longest day of the year because from then on the days are getting shorter!
As for ‘British Summer Time’ – this is just a name chosen to indicate when the clocks ‘go forward’ by one hour as part of the UK’s daylight saving time practice – it doesn’t indicate when the summer beins. It varies between countries (in 2014 it was March 9th in USA but March 30th in most of the rest of the world) and is given various names: In the Australia it is called ‘Eastern Summer Time’, but on the west coast of USA it is called ‘Pacific Daylight Time’.
Answer by Dr Stu
Question from Natahsa B via Facebook
Links: Find out more about the astronomical calendar reckoning at Almanac.com, along with an explanation of why the summer is hot and the winter cold.
Image: Carol Lin, on Flickr