[ad_1]
We usually associate the term "Blue Moon" with one month containing two full moons. Nothing like this happens this month, and yet May 18 still brings a Blue Moon – at least according to the rules established by the editor of an almanac almost a century ago .
A few months ago, I wrote about why Easter 2019 should have fallen in March as opposed to April, based on astronomical considerations.
This year, the spring equinox was at 5:58 pm EDT (8:28 pm GMT) March 20, followed less than 4 hours later by a full moon – officially the first full moon of spring.
Related: What's a blue moon?
However, ecclesiastical rules do not recognize that spring arrives at the earliest on March 21st. Easter, celebrated on the first Sunday after the first full moon of spring, was postponed until April 19, after the next full moon.
And now, here is another unusual artifact of this near-coincidence between the vernal equinox and the full moon of March: this Saturday brings us the full moon of May, and it will be a blue moon.
But, wait a minute, ask yourself if a blue moon is not defined as the second full moon that occurs during a calendar month? The full moon of the 18th is the only full moon of this month. So how can we call it a blue moon?
Yet it is a blue moon, but only if we follow what is now a somewhat obscure rule. This rule was in fact the original definition of the blue mark of the full moon.
The rule of the almanac
In the July 1943 issue of Sky & Telescope magazine, a column of questions and answers referred to the term Blue Moon. The unusual term was quoted in a copy of the 1937 edition of the now-defunct Almanac Maine Farmers.
The almanac page of the month of August 1937 gives a calendar meaning to the term Blue Moon. This explanation said that the moon "usually comes full 12 times a year, three times a season". Sometimes, however, there will be a year where there will be 13 full moons during a year, not the usual 12. "This was considered a very unfortunate circumstance," continued the almanac, "and this upset the regular arrangements of the parish feasts, for which reason 13 has come to be regarded as an unlucky number."
And that extra full moon also meant that one of the four seasons would contain four full moons instead of the usual three. When a particular season has four moons, the third one apparently called a blue moon so that the fourth and last could continue to call the late moon.
So where did we get the "rule of two full moons in a month" that is so popular today?
Major misunderstanding!
Again, look at the pages of Sky & Telescope. This time, on page 3 of the March 1946 issue, James Hugh Pruett wrote an article, "Once in a Blue Moon," in which he referred to the term Blue Moon and the S & T article. July 1943. Pruett had unfortunately reached this conclusion:
"Seven times in 19 years, there were – and still are – 13 full moons in a year, that gives eleven months with a full moon and one with two people, this second of a month, as I understand it. well, called Blue Moon. "
Pruett's explanation in 1946 was, of course, false and it might have been completely forgotten without its use by Deborah Byrd in his famous NPR program "StarDate" on January 31, 1980. During the In the next decade, Pruett's misinterpretation accentuated with a new audience of baby boomers, and today his "rule of two moons in a month" is recognized around the world.
Meanwhile, the rule of the Maine Farmers' almanacs had been forgotten.
As noted above, this publication has long since ceased operations. You must not confuse it with the almanac of the farmers, which has been publishing continuously since 1818 – but fortunately it is based in Lewiston, Maine.
Not quite "complete" … and not literally "blue"
So, in keeping with the old "Almanac Rule of Maine," for the spring of 2019, we have four. full moonsMarch 20th, April 19th, May 18th and June 17th. The third full moon – the Blue Moon according to the initial rule set by the Maine Farmers' Almanac – comes this Saturday, the moon officially becoming full at 5:11 pm EDT (22:11 GMT).
This means that for much of North America, the moon will be just beyond its final phase – actually a waning gibbous moon – when it will arrive at the horizon at dusk of the night. Of course, this moon will always be full to everyone who sees it, even if it will still be slightly slightly rounded.
And do not expect to see the moon shine with a bluish hue. In the past, very unusual atmospheric circumstances have made the moon (and sun) bluish, caused by aerosols injected into the atmosphere, such as volcanic ash and dust (after volcano eruption). Krakatoa in August 1883) or soot suspended in the air from forest fires (as in western Canada in September 1950). But nothing extraordinary happened in the last days or weeks. The moon of this weekend should have the appearance of the color that we are used to seeing.
Here at Space.com, we have posted many stories regarding the differences between the two Blue Moon definitions over the years. And it turns out that the last time we had a Blue Moon based on the rule of "four full moons in a season" was also in May … from 2016.
Consider this column as an updated version for 2019.
Upcoming Attractions
So, when are the next Blue Moons after this Saturday?
If you follow Pruett's "two complete moons in a month" rule, the next Blue Moon will also be spooky: this will happen on Halloween (October 31), 2020. But if you still stick to "Rule of "Almanac Maine", this will not happen again until August 19, 2024, which will bring the third full moon out of four during the summer of this year.
So, what definition of Blue Moon tickles your fantasy? Is it the second full moon of a calendar month or the third full moon of a four season?
Maybe it's just one or maybe both. We leave you the final decision.
Editor's note: If you take an amazing photo of the Blue Moon in May 2019 and want to share them for a story or a photo gallery, send pictures and comments to [email protected]!
Joe Rao is an instructor and guest speaker in New York Hayden Planetarium. He writes on astronomy for Natural History Magazine, the Farmer's Almanac and other publications, and he's also a meteorologist at the camera for Verizon FiOS1 News in the Lower Hudson Valley in New York. Follow us on twitter @Spacedotcom and on Facebook.
[ad_2]
Source link