If something happens once in a blue moon is happens only very rarely.
once in a blue moon意思是非常罕見(jiàn)的事。
An actual blue moon-that is, the appearance of a second full moon in the same calendar month-occurs every 32 months or so.
真正的藍(lán)月亮——是指 ，一個(gè)月内的第二次滿月——大約每32個(gè)月出現一次。
He’s the kind of player that comes along once in a blue moon.
他是那種(zhǒng)百年不遇的天才球員(yuán)。
This is a chance once in a blue moon.
這是個千載難逢的好機會。
