Last Blue Moon till 2015 shows up Friday night, but only for some

This photo of a blue moon was taken from Boca Raton, Fla., on New Year's Eve 2009. (LiveScience photo)Friday night's Full Moon is being called a Blue Moon, but whether that's true is highly dependent on where you live and what definition you use.

It does satisfy the definition of 'the second Full Moon in a calendar month,' as long as you are in the right time zone. It will still be Aug. 31 when the Moon becomes full if you live in Canada and anywhere else west of the time-zone that includes China, Central Russia, Central Indonesia, Singapore, Malaysia, the Philippines and Western Australia. If you are anywhere in or east of those areas — for example in Japan, Korea, Eastern Russia, Eastern Indonesia, Central and Eastern Australia, New Zealand — out to the the International Date Line, it will not be a Blue Moon by that definition. After all, in those places, it will already be Sept. 1 when the Moon reaches its Full stage.

The next Blue Moon fitting this definition won't be until July of 2015 and the last one showed up in March 30, 2010. Only the areas that aren't going to see one tonight witnessed it two years ago.

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When the moon actually appears to be coloured blue is also highly dependent on where you are. This only happens when there are a lot of fine particles in the atmosphere, for example during wide-spread forest fires or after a volcanic eruption. In September 1950, smoke from muskeg fires in Alberta spread across the rest of Canada, causing both the Moon and the Sun to look blue. The Moon also appeared blue for almost two years after the eruption of Krakatoa in 1883. There were other reports of Blue Moons after eruptions from Mount St. Helens in 1980, El Chichon in Mexico in 1983 and Mt Pinatubo in 1991.

People in Saskatchewan and Manitoba may see this tonight, since smoke from fires in Idaho has been blowing into those two provinces for the past few days. If you head to southern Italy, Guatemala, central Chile or Argentina, volcanic ash may give you a Blue Moon there too.

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The third common definition — the one used by the The Old Farmer's Almanac and that isn't dependent on fine particles or time zones — states that it's 'the third Full Moon in a season with four Full Moons.' In the northern hemisphere Summer lasts from June 20/21 to Sept. 22. Full Moons appeared on July 3 and Aug. 2 and there will be one tonight and on Sept. 30. That's only three Full Moons for this Summer, so tonight is not a Blue Moon by this definition.

The last time we had a Farmer's Almanac type of Blue Moon was Nov. 21, 2010, and the next one won't be until August of next year.

Regardless of your definition, it looks like most of the country should have clear enough skies tonight to see a moon of some kind, so go take a look.

If it actually looks blue to you, we'd like to hear about it, so please come back and leave a comment!

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