January 2018 is astronomically special. It is hosting two full moons. One was on Jan. 1 and the second is Jan. 31. The most common definition of a “blue moon” is the second full moon in a month. This happens because the lunar cycle is 29 days, and all but February have more days. So, if a full moon occurs at the beginning of one of these long months, then there can be a blue moon. Another definition is the fourth full moon in a quarter.
January’s full moons also occur when the moon is at perigee. This is the point in its elliptical orbit when it is closest to the Earth. The moon is slightly larger than average: a super moon.
So watch out for the blue moon, and to see the celestial wonders come by the observatory on the first Friday each month from sunset to 10 p.m.: humbleisd.net/observatory.
By Dr. Aaron B. Clevenson
Observatory Director, Insperity Observatory