Tuesday, May 01, 2007

Once in a Blue Moon

Yes, stargazing is still my obsession.

How rare is a full blue moon? (From Earth & Sky)

Tonight's Sky for Tuesday, May 01 2007

The moon will look full tonight, lighting the night from dusk till dawn. In the Americas, though, the moon won’t be truly full till tomorrow morning, at 5:09 a.m. Central Daylight Time. For the Americas, tomorrow’s full moon will be the first of two full moons in May. The second full moon to occur in a single calendar month is popularly known as a blue moon. We elaborate on today’s radio show.

Every 19 years, the phases of the moon recur on (or near) the same calendar dates. So in 2026, there will be two May full moons. Once again, the second full moon will be dubbed a blue moon.

This famous 19-year cycle reveals how often blue moons occur. Every 19 years, there are 235 full moons – yet only 228 calendar months. Therefore, the 7 leftover full moons (235-228=7) have to share the same calendar month with another full moon. That gives 7 blue moons in 19 years.

Yet, there’s one big hitch! February of 2018 has no full moon whatsoever. That’s another displaced full moon that falls right into the lap of March. So that’s a total of 8 blue moons for the next 19 years.

Written by Bruce McClure, 1 May 07

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