Describe the double meaning of the expression “once in a blue moon.”​


What will be the ideal response?


ANSWER: For blue suns to appear, the size of the suspended particles must be similar to the primary wavelengths of visible light. When these particles are present, they tend to scatter red light more than blue, which causes a bluing of the Sun and a reddening of the sky. Although rare, the same phenomenon can happen to moonlight, making the moon appear blue; thus, the expression “once in a blue moon.” (The term “blue moon” also refers to the second full moon in a calendar month that has two full moons).​


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