Monday, July 27, 2015

Blue Moon is coming

Typically we see only one full moon per month, but every once in a while we will see two. This is called a "Blue Moon".  Its not a common place event, and thus the term "Once in a blue moon", has come to mean over the years, something rare or not seen that often.

This year's Blue Moon comes at the end of July. The first took place July 2nd, and the next will be on July 31st.

Will it really turn blue?
Not really... but it has been known to happen. For it to really turn blue the atmosphere needs something to bend the light or mess with it somehow.

  • Some things that can turn it blue can be ash from a volcano or huge forest fires. 

This brief history on truly "Blue Moons" comes from ""

A truly-blue Moon usually requires a volcanic eruption. Back in 1883, for example, people saw blue moons almost every night after the Indonesian volcano Krakatoa exploded with the force of a 100-megaton nuclear bomb. Plumes of ash rose to the very top of Earth's atmosphere, and the Moon became an azure-colored disk.

Krakatoa's ash was the reason. Some of the plumes were filled with particles 1 micron wide, about the same as the wavelength of red light.  Particles of this special size strongly scatter red light, while allowing blue light to pass through. Krakatoa's clouds thus acted like a blue filter. People also 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. Sky watchers in western parts of the USA and Canada, where wildfires are in progress, could experience this phenomenon.

The blue areas in the color-enhanced image (right) are caused by Titanium in lunar soil.
Check this this cool picture comparing a regular looking moon with a "Blue Moon" photographed by Giuseppe Petricca of Pisa, Italy. The snapshot was taken on July 25th, 

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