Definition: a phenomenon whereby the moon appears bluish owing to smoke or dust particles in the atmosphere.
The reason the second definition of blue moon exists is down to an error originally made by amateur astronomer James Hugh Pruett (1886–1955). He misunderstood the basis for calculating the seasonal Blue Moon and wrote that a Blue Moon was the second Full Moon in a month in an article published in Sky & Telescope magazine in 1946. This erroneous definition since spread, particularly after it was quoted in a popular radio program called StarDate in 1980 and then appeared as an answer in a 1986 version of the board game Trivial Pursuit. Today, it is considered a second definition rather than a mistake.A Moon that actually looks blue, however, is a very rare sight. The Moon, full or any other phase, can appear blue when the atmosphere is filled with dust or smoke particles of a certain size; slightly wider than 0.7 micron. The particles scatter the red light, making the Moon appear blue. This is known as Mie scattering, and can happen for instance after a dust storm, a forest fire, or a volcanic eruption.
Eruptions like the ones on Mt. Krakatoa, in Indonesia (1883), El Chichon, Mexico (1983), on Mt. St. Helens (1980) and Mount Pinatubo (1991) are all known to have made the moon look blue. Some people even suggest that the term once in a Blue Moon is based on these rare occasions, rather than the Full Moon definitions.
No comments:
Post a Comment