| 词汇 | once in a blue moon |
| 词源 | once in a blue moon. Seldom, rarely, as in “We go to the movies once in a blue moon.” The moon does rarely appear blue due to the actions of dust particles in the upper atmos- phere. It is also said that the moon turned bluish for a time in 1883 when colored by volcanic ash from the eruption of Kraka- toa in Java. Another meaning of blue moon is “The second full moon in the same calendar month,” which comes to about one blue moon every three years. |
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