Modern astronomical summer begins at the summer solstice (longest day) which is around 21st June and meteorological summer begins on 1st June.
However, a much older calendar had summer starting on 1st May, in which case midsummer is around the summer solstice.
It can be confusing but you might ask how can May be in both spring and summer. It depends which calendar you use. On the old calendar it was the first month of summer; now it is regarded as the last month of spring.
Modern astronomical summer begins at the summer solstice (longest day) which is around 21st June and meteorological summer begins on 1st June.
However, a much older calendar had summer starting on 1st May, in which case midsummer is around the summer solstice.
It can be confusing but you might ask how can May be in both spring and summer. It depends which calendar you use. On the old calendar it was the first month of summer; now it is regarded as the last month of spring.