Equinoxes and solstices: start of the season or mid-season?

Question

In the United States, the upcoming autumnal equinox is marked on most calendars as the "first day of autumn." Similarly the solstices are commonly called the "first day of summer" and "first day of winter." However in most other languages -- and even in older discussions in English -- the solstices have names like "Midsummer's Day" and "Midwinter's Day." Is there some sound reason (e.g. typical temperatures, asymmetrical sunrise/sunset times, thermal inertia, etc.) to consider a solstice as the first day of a new season, rather than the middle? Also (perhaps less on-topic) is there any record of when the change in nomenclature took place in the U.S.? Are there similar discrepancies in other English-speaking countries or in other cultures?

Answer 1

First, equinox means equal night and so their dates are fixed- although if we are being picky it is equal amount of time with the sun above and below the horizon (not equal light and dark since twilight exists). [If we are being more picky we technically measure sunrise from when the top of the sun first comes above the horizon, but sunset when the sun fully sinks below the horizon and we should instead measure it first contact to first contact or center to center.] The solstices are set halfway in-between. The midsummer's and midwinter's day refer to cross-quarter days- Groundhog Day, May Day, Lammas, and Halloween are the traditional cross-quarter days which are halfway in-between the solstices and equinoxes. Some societies have used the cross-quarter days as the start of seasons, which would then make the equinoxes and solstices the middle of the seasons. The main reason usually given for why the change is the slow atmospheric and surface temperature response to the change in amount of sunlight. For example the peak heat of summer usually isn't at the solstice, but after it (around the cross-quarter day) despite the amount of solar radiation decreasing during this time. I would recommend looking into the etymology of the words and frequency for digging into how/when this changed.