A Blue Moon means that its is the second full moon in a month — there was a full moon on July 2nd and the second one on July 31. The rare event occurs every 2 1/2 years, and has nothing to do with its color.
Geoff Chester of the US Naval Observatory said that the traditional definition of blue is two full moons in a calendar month. The term “Blue Moon” is not referred to the color of the moon, but a blue moon can still happen in certain conditions. NASA has explained that a true Blue Moon would require volcanic eruption. For instance, in 1883, Indonesia witnessed a blue moon for several nights after the volcano Kraktoa exploded.
“The truth is you are more likely to see a red moon versus a blue moon and especially at this time of the year,” said Jodi Hughes, Global News weather specialist.
The plumes of ash reached the atmosphere, and the moon turned blue as the particles scatter red light, and blue light filters through it, which is a rare occurrence. Forest fires can also influence the color of the moon, if the moon is lying low, and it can look red due to the aerosols in the atmosphere. The same applies to the red color of the sun during sunset. Aerosols from a volcanic eruption are larger than the aerosols in a forest fire, and they tend to scatter blue light, the red acts like a filter for the sun or the moon.
Several people took posted pictures of the Blue Moon on Friday night. The next Blue Moon will be in January 2018. NASA released a video explaining the rare celestial event. Bob Berman, an astronomer said that professional astronomers and most backyard amateurs, pretty much ignore it.