What is the difference between climatological and astronomical summer?

Dear Tom,
You sometimes refer to “climatological summer.” What is the difference between a climatological summer and a calendar season?
Barbara Wisemann, Evanston
Dear Barbara,
Climatological (or meteorological) summer refers to the three warmest months of the year in the Northern Hemisphere, the months of June, July and August. Meteorological autumn begins on September 1 and runs through November, meteorological winter starts on
December 1 for three months, followed by meteorological spring on March 1. Seasons on the calendar refer to astronomical seasons, based on the sun passing a predetermined point in the sky. Summer begins when the sun passes the solstice, its farthest point north of the equator, usually in June 21 (but the exact time changes from year to year).

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