Air Date: Week of February 5, 1999

This week, facts about...blue moons, two in the first three months of 1999.

Transcript

KNOY: January had 2, there'll be none this month, but 2 again come March. This year's dance between the moon and the calendar puts us in the midst of a cycle of 2 full moons: the first a white full moon, the second blue. It takes the moon an average of 29-1/2 days to orbit the Earth, yet our months number in days from 28 to 31. That means blue moons happen only every 19 years. The blue moon is the second of the 2 full moons, and it's only appeared to be truly blue twice that we know of, once in the 1880s in the wake of Krakatoa's eruption, and again in the 1950s after a series of massive Canadian forest fires. The volcanic dust and smoky haze from those events scattered the moon's red light rays, leaving the blues and greens to shine through. The phenomenon of 2 blue moons in a year is a rare event indeed. The last time it occurred was in 1915, the same year Albert Einstein published his General Theory of Relativity. And that was surely something that happens only once in a blue moon. And for this week, that's the Living on Earth Almanac.