I only go to the cinema once in a blue moon.

我只是在稀有的情况下去电影院。

She visits her old friends once in a blue moon.

她很少在很久的时候去看望老朋友。

We have a chance to meet once in a blue moon.

我们有一次稀有的机会见面。

He takes a vacation once in a blue moon because he is always busy.

因为他总是很忙，他很少度假。

They throw a big family reunion once in a blue moon.

他们很少举行一次大型家庭聚会。