Blue moon rising: Friday’s rarity explained

A blue moon will shine over planet Earth on Friday. Good luck for the Royals? Well, they’re playing in Toronto — against the Blue Jays. And while the moon will be full, it won’t be blue. Here’s what this blue moon hubbub is all about.

What it is

A second full moon to occur within a calendar month is called a blue moon, according to the National Weather Service. According to an older definition, it is also described as the third full moon in an astronomical season that contains four full moons instead of the usual three.

Moons can be blue, but this one won’t be

The “blue” moon will look just like any other full moon. But moons actually can appear blue, usually when smoke or dust particles are in the atmosphere, like the stuff volcanoes belch into the air.

A classic example: When the Indonesian volcano Krakatoa erupted with the force of a nuclear bomb in 1883, it shot so much ash into the sky that the moon looked blue for many nights.

Last time we saw it

Blue moons tend to show up every three years. The last one seen in the Americas rose in August 2012.

Unusual celebrations

Astronaut Neil Armstrong, the first man to walk on the moon, was laid to rest on the same day as the last blue moon in 2012. His family suggested that a fitting tribute would be to look up at the moon and give him a wink. It’s still a nice sentiment today.

Careful what you wish for

Fox affiliate WTXF-TV in Philadelphia asked viewers for their “moon pictures” on Wednesday night.

Moon, of course, can be defined any number of ways. Some viewers sent in NSFW images.

And hey, is that Keith Moon?

When the next blue moon will appear

Jan. 2, 2018.

This story was originally published July 30, 2015 at 11:55 AM with the headline "Blue moon rising: Friday’s rarity explained."