This article explains a celestial phenomenon relevant to science and technology sections of UPSC and SSC exams. Prelims may test definitions and historical context of blue moons; mains could cover astronomical events and their causes. The connection to the Krakatoa eruption also touches on atmospheric science and disaster impacts, adding interdisciplinary value.
Key Takeaways
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A blue moon occurs when two full moons appear in a single calendar month; the second full moon is called a blue moon under the modern definition.
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The modern definition of blue moon became popular in 1946 when writer James Hugh Pruett misinterpreted old copies of the Maine Farmers’ Almanac.
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There is also an older seasonal definition: when an astronomical season has four full moons instead of three, the third full moon is called a blue moon; the next seasonal blue moon will occur on 20 May 2027.
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The name 'blue moon' is a calendrical term and has nothing to do with the Moon’s actual colour.