When a February within that 19-year period has no full moon, which happens in 2018, that's when two blue moons can happen in the same calendar year. This will be the second full moon in a month, also called the Blue Moon. This will be the biggest supermoon of the year.
A typical Supermoon is 30% brighter and 16% larger than when the full moon is at it's farthest distance during it's orbit.
Check out the Roseland Observatory's handy guide to seeing the supermoon at its best below. People can witness it from any place where the western horizon is clear.
But if you miss tonight's moon - never fear, the January 31 moon will be "extra special" according to Nasa.
In addition, the so-called "full supermoon" appeared 30 percent brighter than an average full moon, according to NASA. It will be a neat site to see if you can fearless the extreme cold tonight, because we have a nice snow pack outside, which will reflect a lot of the light from the moon. Totally eclipsed moons are for this reason called "blood Moons". On January 31, a Blue Moon will rise in the sky. This moon will also cause particularly high or king tides.
"The supermoons are a great opportunity for people to start looking at the moon, not just that once but every chance they have!" said Noah Petro, a research scientist from NASA's Goddard Space Flight Center.
The largest recent supermoon occurred in a year ago. That was the first and only supermoon of 2017. "It didn't look at all brighter than normal".
This happens on a monthly basis, but occasionally the point of perigee aligns with a new or full moon and results in a "perigean spring tide".
Another Supermoon is on the calendar for January 31, 2018.
The Jan. 1 occurrence is a wolf moon, the term for the first full moon of the year.