June 21

In common years it is always in ISO week 25.This day marks the summer solstice in the northern hemisphere and the winter solstice in the southern hemisphere, and thus is the day of the year with the longest hours of daylight in the northern hemisphere and the shortest in the southern hemisphere.
See more at Wikipedia.org...

Noun
1. June 21, when the sun is at its northernmost point
(synonym) summer solstice, midsummer
(hypernym) solstice
(part-holonym) June