'Blue Moon' Night Sky Show - It Won't Happen Again Until 2018! (+Video)

If anything unusual happens to you Friday, you’ll be right to say it was “Once in a Blue Moon,”

For the second time this month, the Moon is about to become full.  There was one full Moon on July 2nd, and now a second is coming on July 31st.  According to modern folklore, whenever there are two full Moons in a calendar month, the second one is “blue.”

Most Blue Moons look pale gray and white.
Nevertheless, on rare occasions the Moon can turn blue.

People saw blue-colored Moons in 1983 after the eruption of the El Chichon volcano in Mexico. And there are reports of blue Moons caused by Mt. St. Helens in 1980 and Mount Pinatubo in 1991.
Forest fires can do the same trick.  A famous example is the giant muskeg fire of Sept. 1953 in Alberta, Canada.  Clouds of smoke containing micron-sized oil droplets produced lavender suns and blue Moons all the way from North America to England.  

At this time of year, summer wildfires often produce smoke with an abundance of micron-sized particles–just the right size to turn the Moon truly blue.

On the other hand, maybe it will turn red.  Often, when the Moon is hanging low, it looks red for the same reason that sunsets are red.  The atmosphere is full of aerosols much smaller than the ones injected by volcanoes.  These aerosols scatter blue light, while leaving the red behind.
For this reason, red Blue Moons are far more common than blue Blue Moons.
Sounds absurd? Yes, but that’s what a Blue Moon is all about. Step outside at sunset on July 31st, look east, and see what color presents itself.

http://science.nasa.gov/science-news/science-at-nasa/2015/27jul_bluemoon

Image credit: NASA