"Ever mention something that happens “once in a blue moon”?
Well brace yourselves—that moon will be here at the end of the month.
August 31, 2012
A blue moon is full moon that occurs as the second full moon in a given month. Blue moons are not typically blue in color — that happens only, well, once in a blue moon, but there is the possibility for a hint of blue in any full moon (more on this below). The definition of blue moon as the term is used today began when a writer made a mistake.
The phrase “blue moon" is "a creature of folklore," explains Philip Hiscock, a folklorist at the Memorial University of Newfoundland. “It’s the second full moon in a calendar month.”
Hiscock helped figure out where the term came from. Long ago, “blue moon" was used to describe absurd things. In 1946, James Hugh Pruett (1886-1955), an amateur astronomer, was writing in Sky & Telescope magazine. Pruett “made an incorrect assumption about how the term had been used in the Maine Farmers’ Almanac — which consistently used “blue moon” to mean to the third full moon in a season that contained four of them (rather than the usual three),” Sky & Telescope editors later explained. The error had been repeated in a syndicated radio program in 1980.
Hiscock and Texas astronomer Donald W. Olson helped the magazine sort all this out and admit the mistake back in 1999. The error led to the widely accepted definition of blue moon today: the second full moon in a given month. A blue moon occurs roughly once every 2.7 years.
The next blue moon, according to this folklore, will be Aug. 31, 2012. (There are two full moons in August, the first one being Aug. 1.) If you miss this one, you’ll have to wait three years for the next blue moon. There will be two full moons in a single month in July 2015 (July 1 and 31).
But can the moon really be blue? Yes, scientists say.
If there’s been a recent forest fire or volcanic eruption that pumped significant smoke or ash into the upper atmosphere, it is possible for the moon to take on a bluish hue. Just such an event made the moon turn blue in late September, 1950, when smoke from a forest fire in Canada drifted down to cause a blue moon over eastern North America. The eruption of Mount Pinatubo in June 1991 created blue moons from various perspectives around the planet.
The phrase “once in a blue moon” — meaning something very rare — dates back to 1824.
On May 20, our moon will pass between the Earth and the sun, creating a brilliant annular solar eclipse for some viewers and an equally amazing partial solar eclipse for many others.
An annular solar eclipse happens when the moon is at a certain distance from the Earth, so that it appears relatively smaller than the sun; in a total eclipse, the moon appears to be the same size as the sun. This all happens because the moon’s orbit around the Earth isn’t a perfect circle but rather is an ellipse, putting it sometimes a bit further from the Earth than others.
An annular eclipse gets its name due to the ring, or annulus, that forms around the moon when the eclipse reaches maximum.
Due to the size of the moon compared to the size of the sun (and the fact that the moon can’t block the sunlight for everyone on Earth at once), not everyone will be able to see this annular eclipse. Only a relatively small number of people will be in just the right spot to see the annulus. But if you’re outside of the ideal viewing area, by no means are you out of luck!
Some of the major cities and places that lie along the path of best viewing for this annular eclipse include Tokyo; Alaska’s Aleutian Islands; Redding, California; central Nevada; southern Utah; northern Arizona; and Albuquerque, New Mexico.
If you live anywhere in the western or midwestern United States or Canada, you’ll be able to see a partial eclipse. If you live in East Asia and near the Pacific Ocean, you’ll also be able to see the partial eclipse. Unfortunately, if you’re on the east coast of the United States, the sun will have already set by the time the eclipse starts.
There’s a lot more to the science behind why eclipses happen and why only some parts of the planet can see the annulus. If you’d like to know more, we have a special article dedicated to explaining why an eclipse happens.
The eclipse will begin on the west coast of the United States at 6:30 p.m. PDT on May 20. It travels from west to east, so the times that it starts, reaches maximum, and ends will be different in your area. The best tool for figuring out exactly when the eclipse will be in your neck of the woods is on NASA’s eclipse page, where you’ll find an interactive Google Map showing the exact times for any place you click on.
Remember that even if you’re outside of the main viewing area (marked by blue lines on NASA’s Google Map), you can still see a partial eclipse, so click near your city’s location to find out when! NASA’s site gives everything in UTC time, so you’ll need to convert it to your local time. Head over to WorldTimeServer.com to make a quick conversion.
Always be sure that you never look at the sun directly, even during an annular solar eclipse. You’ll want to use special eyewear or view the eclipse through a makeshift pinhole projector. Check out our guide on how to safely view the May 2012 annular solar eclipse for more information.