Shame on you Lady P... were you not at Hastings when the Spirit of Summer, the Jack in the Green was released?

Part of the problem is that the calendar does not exactly match up with the lunar phases.

If we start the calendar year on Monday January 1st, week 26 (half of 52) begins 25th June, more or less Midsummer. If the Spring Equinox is around March 22nd, that falls in week 16. The Autumnal Equinox is around September 21st, or week 38.

Therefore, if Summer begins on May 1st, there are about 8 weeks til midsummer. Taking that as the central point, summer ends about 8 weeks later in the middle of August.

Midwinter's day, Dec 21st is in the calendar as week 51, 13 weeks after the Autumnal Equinox. Add 13 weeks to that and you come around to the beginning of March. Therefore, Spring is actually 3 weeks at the beginning of March and Autumn is the 4 weeks between the middle of August and the Autumnal Equinox...

See, it's easy!