The moon is the 13th full of the year

The full moon on December 28 is quite a rare phenomenon, because this is the 13th full moon that humanity saw in 2012.

In some years people will witness the full moon 14 times.

The full moon is at 10:21 on December 28 at UTC (17h21 on the same day in Hanoi), Livescience reported.

Due to the full moon appearing only once a month, and only 12 months a year, people often see the moon 12 times a year.

However, the 13th full moon phenomenon always occurs in stages, since the time between the full moon is 29.5 days. If we take the number of days in a year divided by 29.5, we get a result of 12.37. That means the moon is 12.37 times a year. Thus, every 2-3 years, we will meet a lunar year with 13 full moon. That year the full moon will appear twice in a month. It is called the "blue moon".

This year the "blue moon" phenomenon happens twice in August. We have to wait until 2015 to witness the same event.

Even in some years people witnessed the full moon 14 times. In those years, "blue moon" will appear twice in two months. The year when the full moon appeared 14 times occurred in 1999 and will continue to happen in 2018.