This is why we have Blue Moons:

There are 12 months in one year; some months have 30 days and some months have 31 days. However, the orbit of the moon is 29.53059 days in one month. In one century, there are 1,200 months and there will be 1,234.83 full moons, so a blue moon will happen 36.83 times every 100 years, or once in 2.72 years.

If you miss this blue moon, the next Blue Moon will be on 2nd July 2015.

?. ? 31 ?

?.?  ? ? ? ? 31 ? 2555 ? ? (Blue Moon) ? ? ? (Full Moon) ? 1 ? ? 2 ? ? “?”  ? Once in a blue moon ? ? ? ? Rarely ? 

             ? 1 ? ? 12 ? ? 30 ? ? 31 ? ? 29.53059 ? ? 1 ? 1200 ? ? 1236.83 ? ? 36.83 ? ? 2.72 ? ? 3% ? ?

? 31 ? 2555 ? ? 18.18 ?. ? 20.57 ?. ? 1 ? 2555 ? 05.37 ?. ? ? ? Blue Moon ? 2 ? 2558