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I'm not sure which sourcesI'm not sure which sources you're Googling, but it's fairly simple to figure out. If (approximately, as it can vary) the 21st of June is Midsummer (as you yourself have correctly stated), then the beginning of Summer would have to be the first of May, as it has been celebrated by many cultures in the Northern hemisphere for quite a long time. As for being obsessed with the Equinoxes and Solstices, it would seem to me that you're fairly obsessed with attacking their validity.