Thursday, May 31 brings us the second of two full Moons for North Americans this month. Some almanacs and calendars assert that when two full Moons occur within a calendar month, that the second full Moon is called the “Blue Moon.”The full Moon that night will likely look no different than any other full Moon. But the Moon can change color in certain conditions.After forest fires or volcanic eruptions, the Moon can appear to take on a bluish or even lavender hue.

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The phrase “Once in a blue Moon” was first noted in 1824 and refers to occurrences that are uncommon, though not truly rare. Yet, to have two full Moons in the same month is not as uncommon as one might think. In fact, it occurs, on average, about every 32 months. And in the year 1999, it occurred twice in a span of just three months!

Source: The Truth Behind This Month’s Blue Moon, Joe Rao

Mai multe despre Blue Moon pe Wikipedia - link

Update: 

Kentucky Blue Moon Celebration May 31-June 1 At Lake Barkley State Resort Park - link

Once in a Blue Moon - link

Photography copyright: NASA

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