Funny enough, the 31st of December is in fact a blue moon. Because the moon takes 29.5 days to orbit around the earth, every now and then you can end up with two full moons within the same month and the second one is known as the "blue moon" (nothing to do with colour).
On adverage this event occurs once every 2.5 years and the fact that it will happen on New Years eve is quite amaizing. The last time it happend on this date was back in 1990 and the next time it will happen won't be till 2028.
I hope you all enjoy your night and remember this event only happends once in a blue moon
Cheers