EarthSky reports
January has two full supermoons. The 2nd one comes on January 31. As the 2nd full moon of the month, it carries the name Blue Moon. Plus, it’ll undergo an eclipse!
January 1, 2018, full supermoon over Seattle, Washington from Gary Peltz. See more photos of the January 1, 2018, supermoon.
A supermoon is a new or full moon closely coinciding with perigee – the moon’s closest point to Earth in its monthly orbit. An astrologer, Richard Nolle, coined the term supermoon over 30 years ago, but now many in astronomy use it as well. Supermoons have entered the popular culture (check out Sophie Hunger’s music video in this post, for example), and they can cause real physical effects, such as particularly high and low tides. According to the definition of supermoon coined by Nolle, the full moon of December was 2017’s only full supermoon. January 2018 will have two full moons – on January 1 and 31 – and both are supermoons. Follow the links below to learn more about supermoons.
What did astronomers call these moons before “supermoons”?
Natural History Wanderings 
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