In this system, summer begins on June 1 and ends on August 31. Therefore, the summer solstice is not considered to be the first day of summer, meteorologically speaking. Astronomically, however, the first day of summer is said to be when the Sun reaches its highest point in the sky, which occurs on the summer solstice (June 20–22).
: https://www.almanac.com/content/first-day-summer-summer-solstice

