June summer solstice full moon is rare and unpredictable...and whose light will be upon those who would venture outdoors during the event.
This is not much harder to predict than any other full moon. According to
this website, the last full moon on the same GMT day as the June solstice was 1967, almost 50 years ago, and the next will be in 2062. If, by
same day, you mean both events occur within
24 hours of each other - that is, it's the same day in at least one time zone - then it's more common, occurring about once every 19 years. Whether once in 19 years (or even once every 50) is "rare" or not depends, of course, on your definition of "rare"[nb]Transits of Venus, for instance, usually occur twice about every 143 years; the reappearance of Halley's Comet is once about every 76 years.[/nb]; at any rate, this is expected.
Regardless, for the superstitious types that don't like being out under the full moon, rejoice! Since the full moon is always on the opposite side of the ecliptic as the Sun, the Moon will be up the shortest amount of time of the entire year on this night while full (in the northern hemisphere)![nb]For you poor bastards south of the equator, it will be up the longest of any full moon this year, but then, it's not a
summer solstice for you, so that mystical property, whatever it is, will be absent.[/nb]
Everyone needs to keep calm and carry on.