It’s kind of an infrequent occurrence—once every 2.7 years....
If you take a look up at the early morning sky on Saturday, March 31, you will see the last blue moon for the next two and a half years. It peaks at 6:43a.m. CDST time. A blue moon as it’s defined today is the second full moon in a given month. The phrase used to refer to an extra moon during a season’s cycle, but language always evolves and this phrase has, too. So, in 2018, a full moon on March 2, and again on March 31? Blue moon. It’ll be your last chance to see one until Halloween 2020 when the next blue moon happens—and what a great day of the year for that to occur! Despite the name, it will not be the hue of blue. However, true blue-hued moons have happened; when volcanoes erupt, they can show themselves. Krakatoa in 1883, Mount St. Helens in 1980, El Chichon in 1983, and Mount Pinatubo in 1991 all caused a blue-shaded moon in parts of the world. This happens because some of the ash particles are one micron wide, about the same wavelength as red light. This scatters the red li...