<P> Owing to the rarity of a blue moon , the term `` blue moon '' is used colloquially to mean a rare event , as in the phrase `` once in a blue moon '' . </P>
<P> Owing to the rarity of a blue moon , the term `` blue moon '' is used colloquially to mean a rare event , as in the phrase `` once in a blue moon '' . </P>
once in a blue moon origin of phrase
once in a blue moon origin of phrase
rarity of a blue moon
rarity of a blue moon