[Ed. – Look, not to rag on the author here, but did it really take this many words to express the thought that our minds make events “rare” by how we define them? Sure, each night gives us a sky whose precise astronomical alignment hasn’t occurred — depending on how we define the “alignment” — for 20,000 years. But it matters to our minds whether the “alignment” refers to the planets in our solar system lining up as a putative observer moves outward from the sun. “Rarity” is a function of human interest and meaning. Du-uh. That’s notably why it makes perfect sense for there to be a God who arranged for “rare” astronomical events to suggest portents to the minds He gave us.]
Something weird seems to be happening in the heavens. This week marks a coincidence of the full moon and the summer solstice. Some astronomers are calling this combination of maximum moonlight and the Northern Hemisphere’s longest day a rare event.
It comes close on the heels of last month’s rare passage of Mercury in front of the sun, September’s rare pairing of a lunar eclipse with a so-called supermoon, the rare 2014 “tetrad” of lunar eclipses, the rare 2012 transit of Venus, and a plethora of once-in-a-lifetime planetary alignments, one earlier this year, one in 2014 and one in the summer of 2013. Next year there will be a rare total eclipse of the sun.
If these sorts of events are so rare, why do they happen so often? …
The cycles of the moon and sun are predictable, but they aren’t in sync so you would expect bunches and gaps.
But there is still the recent pileup of other rare events to explain – some of them, such as the transit of Venus, much rarer than a solstice full moon. …
[T]here are many ways that different combinations of the sun, moon and planets can align in some interesting pattern. Planetary alignments are always unique, said astronomer Alan MacRobert, an editor at Sky and Telescope. “Whenever there’s an alignment of planets you’ll read that it has not happened in 20,000 years,” he said. But that’s the case of every night sky. … The universe is superabundant with possibilities, and that’s part of what makes astronomy fun.