Anthropology/how did they figure
In the times of Stonehenge,and other ancient structures, based on a calendar. Also sense there is only minutes separating Sunrise on June 20 and June 21, June 22 how were the able to establish Sunrise on June 21 as being the longest day of the year. My only conclusion is that The stone placements on sunrise on June 20, 21, 22, are not separate enough to be that that kind of precision was not important enough.
Hi Robert, You are essentially correct. The difference is so small, it is hardly noticeable. For Stonehenge. the Heal stone has a "bump" and for those three days the sun comes up over the bump. They have chosen the middle day for the celebration since this would seem most logical.
And surprisingly, it is the summer solstice. So, while time was of a more flexible nature back then, they still managed to get it right. The celebration during those time probably lasted the 3 days before and after.