Have you ever heard the expression “every once in a blue moon”? This expression usually refers to a rare event. The moon really appearing to be blue or the theoretical “blue moon” of modern times rarely occurs, thus the creation of the expression “every once in a blue moon.”
The term “blue moon” is believed to have been created in 1883 when the volcano Krakatoa, in Indonesia, erupted. The eruption was credited for creating the loudest explosion believed to have ever been heard in modern history. The eruption also created as ash cloud from which particles floated in the air making the moon appear to be blue for two years after the eruption, thus the came about the term “blue moon.”
The moon appearing to be physically blue has only happened a few times in history. The eruption of Krakatoa being the first recorded appearance of a “blue moon.” Other occurrences were around the time of other volcanic eruptions, Mt. St. Helens in 1980, El Chichon in 1983, and Mt. Pinutabo in 1991. The only occurrence that produced a visual of the moon being blue that was not associated with a volcanic eruption was muskeg fires in Alberta, Canada in 1950 that put particles in the air that caused the moon to appear blue.
The “blue moon” of historical times after the eruption of Krakatoa did not actually refer to the moon appearing to be the color blue. It referred to the rare occurrence of the full moon making an extra appearance during season or a month. The Farmer’s Almanac describes the occurrence as four full moons in one season. A season consists of a three month period and if there were four full moons in a season the third full moon was called the “blue moon,” even though the moon was not actually the color blue.
The modern definition of a “blue moon” is when there are two full moons in a one month period. The occurrence of the “blue moon” on New Year’s in 2010 was an extremely rare occurrence that only happens about once every nineteen years. The “blue moon” on New Year’s 2010 was an extra special phenomenon because it occurred at the same time as a partial lunar eclipse the that was visible in several parts of the world.
The “blue moon” actually occurred on New Year’s Eve in the United States, Canada, Africa, Europe and South America. The moon was not full in Australia and Asia until New Year’s day. The lunar eclipse was visible in the Eastern Hemisphere but was not visible to the Americas.