Is a Blue Moon Really Blue?

Full Moon copyright Jill Henderson 2012By Jill Henderson – Show Me Oz

Tonight we will be treated to a rare blue moon.  Celebrated throughout the ages, blue moons are studied, admired and looked upon with varying levels of wonder and awe.  Of course, a blue moon is the second full moon in a calendar month and happens on average, once every two years, mostly in the months of June, July and August.   But is a blue moon really blue?

While the rain-laden clouds from Hurricane Isaac will block my view of tonight’s blue moon, I’m pretty sure the moon will not really be blue.  That’s not to say that blue moons are never blue – they are.  The term ‘blue moon’ was to coined by the Maine Farmer’s Almanac around 1883.  It was during this time that the Indonesian volcano, Krakatoa, erupted in what some call the most massive volcanic eruption in living history.  The blast from this mega-volcano was likened to a 100 megaton nuclear bomb.  It was heard and felt nearly a thousand miles away.

During the initial explosion, superfine ash was thrust high into the atmosphere and circled the globe.  For years afterwards, many blue moons – and not just the rare second full moon in a month – were seen.   The moon actually appeared to be blue in color because of the size of the ash in the atmosphere; approximately 1 micron, or one-millionth of a meter, in diameter.  Particles this small scatter red light, allowing the color blue to shine through.  So when the light of the full moon passes through the fine ash, blue becomes the predominant color seen by the human eye.  Hence, a blue moon.

While the occasional blue moon may be seen after a large fire or volcanic eruption, they are extremely rare.  Therefore, the modern use of the term blue moon is used to relay a rare occurrence.  Exactly how the second full moon in a calendar month came to be called a blue moon may never be fully understood. However, it likely came about for the simple reason that two full moons in a single month don’t occur very often…about every once in a blue moon.

Like a blue moon, I am posting twice in the same week so that I can spend the holiday with my family.  I hope you, too, have a wonderful holiday, wherever you are!


Jill Henderson is an artist, author and the editor of Show Me Oz
© 2012 Jill Henderson

Excerpted in part from A Journey of Seasons A Year in the Ozarks High Country

Filled with nature notes, botanical musings, back-woods wisdom and just a pinch of hillbilly humor.

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