So "astronomical summer" oddly starts with the day that the incoming solar energy is highest in the northern hemisphere? Ok, that explains why it's used in English, but really it just uses the same definition! The meteorological calendar just appears to use three months, so that is pretty arbitrary.
The most logical definition of astronomical summer and winter imho would have been winter and summer being the quarter-years centered on the summer and winter solstice respectively. Then the astronomical definitions would have been in line with (non-english) language, i.e. mid winter is the shortest day and mid summer is the longest day.
> Midsummer is celebrated on the longest day in some cultures, on the solstice in others
Aren't those the same thing (maybe give or take a day)? Where I live it's celebrated on a weekend near the solstice, which makes even more sense because alcohol.
> So "astronomical summer" oddly starts with the day that the incoming solar energy is highest in the northern hemisphere?
In a way, but you're looking at the effect, not the cause. The solstice is the day where either day or night is the shortest, which is caused by the earth either being at the aphelion or the perihelion (i.e. nearest or farthest points from the sun).
One could reasonably suspect that the solstice dates better represent a period just before the centre of the season rather than the beginning of it, since seasons take a bit of time to move in (at least up here in Canada). Snow won't stay until the ground has cooled enough, for example.
Aphelion and perihelion do not have anything to do with the solstices. They are currently coincidentally 2 weeks apart, but will be months apart in several thousand years.
Midsummer is celebrated on the longest day in some cultures, on the solstice in others, but does not denote the middle of astronomical summer.
Meteorologic summer and winter currently begin weeks before the solstice. https://www.ncdc.noaa.gov/news/meteorological-versus-astrono... has a discussion on the difference.