Midsummer Day falls near the start of modern summer, not its middle
England still calls 24 June Midsummer Day, which sounds odd when summer has barely begun. The name survives from an older reckoning in which summer ran from 9 May to 10 August, with the solstice at its centre. By daylight alone, the longest day really is the middle of the season, not its opening.
Romans using the Julian calendar and Anglo-Saxons in England both counted summer from 9 May, with the solstice on 24 June as the midpoint; in England that date remained a quarter day of the calendar. Much of Europe began summer on May Day. In Gaelic Ireland and Scotland it opened with Bealtaine on 1 May and closed with Lughnasa on 1 August, and in Wales it started with Calan Haf, meaning first of summer. The Chinese solar calendar agrees closely, running summer from the term lixia, establishment of summer, around 5 May to liqiu around 7 August.
Modern meteorologists disagree with all of that, because heat lags behind light. The warmest weeks arrive several weeks after the Sun peaks, so they count June, July and August as summer in the north and December to February in the south. Countries including Russia, Japan, Denmark and Austria follow that convention, as does Ireland's weather service. Some North Americans instead start summer at the solstice, around 20 or 21 June, and run it to the autumn equinox, while monsoon Asia treats March to June, the hottest stretch before the rains, as summer.
Culture sets its own markers. In the United States summer runs socially from Memorial Day weekend to Labor Day, and in Canada from Victoria Day a week earlier. Across Brazil, Argentina, South Africa, Australia and New Zealand, summer brings Christmas and New Year, with long family holidays and school breaks from early December to early February. Sweden's Midsummer is sometimes nicknamed an alternative national day.
Summer weather varies as much as its dates. Mediterranean summers are dry, whereas East Asian ones are rainy under the monsoon. The Atlantic hurricane season runs from 1 June to 30 November and peaks statistically on 10 September, and North American thunderstorms can bring hail and tornadoes, mostly in the afternoon and evening.
Source: Summer
