Once in a blue Moon

Taken by Seh Fong....

This idiom means A very rare event.
According to popular usage, a blue moon refers to the second full moon that occurs in any calendar month.
On average, there will be 41 months that have two full moons in every century.
By that calculation 'once in a blue moon' means once every two-and-a-half years.

I was so lucky can view the blue moon,
which on the new year eve,
and it only happen once in a 19 years with my dear ❤ xueji❤!