The Really Strange Story Behind Sunday's Blue Moon

The moon can appear somewhat blue if there's been a major volcanic eruption that put tons of particles in the air, but otherwise blue moons refer to multiple full moons in certain time frames

A "blue moon" isn't really blue, as this artist rendering suggests. The moon can appear somewhat blue if there's been a major volcanic eruption that put tons of particles in the air, but otherwise blue moons refer to multiple full moons in certain time frames. (Image credit: Dreamstime)

This story was updated at 9:03 p.m. ET.

The full moon of November arrives on Sunday and will bring with it a cosmic addition: It will also be a so-called "blue moon."

"But wait a minute," you might ask. "Isn't a 'blue moon' defined as the second full moon that occurs during a calendar month? Sunday's full moon falls on Nov. 21 and it will be the only full moon in November 2010. So how can it be a 'blue' moon? Related When is the next blue moon?

In fact, the current "two- full moons in one month" rule has superseded an older rule that would allow us to call Sunday's moon "blue." To be clear, the moon does not actually appear a blue color during a blue moon, it has to do with lunar mechanics.

Confused yet??

Well, as the late Paul Harvey used to say -- here now, is the rest of the story:

The blue moon rule

Back in the July 1943 issue of Sky & Telescope magazine, in a question and answer column written by Lawrence J. Lafleur, there was a reference made to the term "blue moon."

Lafleur cited the unusual term from a copy of the 1937 edition of the now-defunct Maine Farmers' Almanac (NOT to be confused with The Farmers' Almanac of Lewiston, Maine, which is still in business).

On the almanac page for August 1937, the calendrical meaning for the term "blue moon" was given.

That explanation said that the moon "usually comes full twelve times in a year, three times for each season."

Occasionally, however, there will come a year when there are 13 full moons during a year, not the usual 12. The almanac explanation continued:

"This was considered a very unfortunate circumstance, especially by the monks who had charge of the calendar of thirteen months for that year, and it upset the regular arrangement of church festivals. For this reason thirteen came to be considered an unlucky number."

And with that extra full moon, it also meant that one of the four seasons would contain four full moons instead of the usual three.

"There are seven Blue Moons in a Lunar Cycle of nineteen years," continued the almanac, ending on the comment that, "In olden times the almanac makers had much difficulty calculating the occurrence of the Blue Moon and this uncertainty gave rise to the expression 'Once in a Blue Moon.'"

An unfortunate oversight

But while LaFleur quoted the almanac's account, he made one very important omission: He never specified the date for this particular blue moon.

As it turned out, in 1937, it occurred on Aug. 21. That was the third full moon in the summer of 1937, a summer season that would see a total of four full moons.

Names were assigned to each moon in a season: For example, the first moon of summer was called the early summer moon, the second was the midsummer moon, and the last was called the late summer moon.

But when a particular season has four moons, the third was apparently called a blue moon so that the fourth and final one can continue to be called the late moon.

So where did we get the "two full moons in a month rule" that is so popular today?

A moon mistake

Once again, we must turn to 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 made a reference to the term "blue moon" and referenced LaFleur's article from 1943.

But because Pruett had no specific full moon date for 1937 to fall back on, his interpretation of the ruling given by the Maine Farmers' Almanac was highly subjective. Pruett ultimately came to this conclusion:

"Seven times in 19 years there were -- and still are -- 13 full moons in a year. This gives 11 months with one full moon each and one with two. This second in a month, so I interpret it, was called Blue Moon."

How unfortunate that Pruett did not have a copy of that 1937 almanac at hand, or else he would have almost certainly noticed that his "two full moons in a single month assumption" would have been totally wrong.

For the blue moon date of Aug. 21 was most definitely not the second full moon that month!

Blue moon myth runs wild

Pruett's 1946 explanation was, of course, the wrong interpretation and it might have been completely forgotten were it not for Deborah Byrd who used it on her popular radio program, "StarDate" on Jan. 31, 1980.

We could almost say that in the aftermath of her radio show, the incorrect blue moon rule "went viral" -- or at least the '80s equivalent of it.

Over the next decade, this new blue moon definition started appearing in diverse places, such as the World Almanac for Kids and the board game Trivial Pursuit.

I must confess here, that even I was involved in helping to perpetuate the new version of the blue moon phenomenon. Nearly 30 years ago, in the Dec. 1, 1982 edition of The New York Times, I made reference to it in that newspaper's "New York Day by Day" column.

And by 1988, the new definition started receiving international press coverage.

Today, Pruett's misinterpreted "two full moons in a month rule" is recognized worldwide. Indeed, Sky & Telescope turned a literary lemon into lemonade, proclaiming later that -- however unintentional -- it changed pop culture and the English language in unexpected ways.

Meanwhile, the original Maine Farmers' Almanac rule had been all but forgotten.

Playing by the (old) rules

Now, let's come back to this Sunday's full moon.

Under the old Almanac rule, this would technically be a blue moon. In the autumn season of 2010, there are four full moons:

Sept. 23

Oct. 22

Nov. 21

Dec. 21

"But wait," you might say. "Dec. 21 is the first day of winter."

And you would be correct, but only if you live north of the equator in the Northern Hemisphere. South of the equator it's the first day of summer.

In 2010, the solstice comes at 6:38 p.m. EST (2338 UT).

But the moon turns full at 3:13 a.m. EST (0813 UT). That's 15 hours and 25 minutes before the solstice occurs. So the Dec. 21 full moon occurs during the waning hours of fall and qualifies as the fourth full moon of the season.

This means that under the original Maine Almanac rule -- the one promoted by Lafleur and later misinterpreted by Pruett -- the third full moon of the 2010 fall season on Nov. 21 would be a blue moon.

Choose your blue moon

So what Blue Moon definition tickles your fancy? Is it the second full moon in a calendar month, or (as is the case on Sunday) the third full moon in a season with four?

Maybe it's both. The final decision is solely up to you.

Sunday's full moon will look no different than any other full moon. But the moon can change color in certain conditions.

After forest fires or volcanic eruptions, the moon can appear to take on a bluish or even lavender hue. Soot and ash particles, deposited high in the Earth's atmosphere, can sometimes make the moon appear bluish.

In the aftermath of the massive eruption of Mount Pinatubo in the Philippines in June 1991, there were reports of blue moons (and even blue suns) worldwide.

We could even call the next full moon (on Dec. 21) a "red moon," but for a different reason: On that day there will be a total eclipse of the moon and, for a short while, the moon will actually glow with a ruddy reddish hue.

More on that special event in the days to come here at SPACE.com, so stay tuned!

The Wicked Fairy

Long, long time ago, the world was doomed with darkness. A powerful evil fairy named Niña ruled the world. Niña is a wingless who lives in lures, a magical forest realm. The animals became the slaves and servant of the wicked fairy. Niña punishes every animals who disobey her.

The world was very dark place to live with indeed. The only light to be found was far away. Niña walks in the winter dark, trailing mist and shadows with her magical wand. Her magical wand protects and give her power. None of the animals try to disobey Niña. Except Eris, a squirrel and Peter who is a rabbit secretly makes fun of the wicked fairy without her knowledge

The Blue Moon Appeared

One Day, it was winter and the blue moon showed up again covering the plains of this insignificant dark world. For Niña it was the perfect moment to travel for she will gain more power. So she travelled to the other side of the world to say her rituals facing the blue moon. The blue moon which appeared only once in 350 years and for Niña this was the perfect moment to strengthen her power.

For the rest of the animals it was assign of relief for they felt like they had been marooned for a long time ago. Eris and Peter plays in the biggest tree in the forest and which was Niña’s house. The tree has a big hole in the middle which caught the attention of Eris. They had never been in the tree for Niña had warned them. Eris walked slowly to the big hole of the tree.” No Eris let’s go back, Niña will punished us!’’ Peter shouted worriedly. But Eris continued to walk to the hole. Eris could barely heard the fast beating of his heart.” Peter, come here. Look what I found.” Eris shouted impatiently. Peter run to Eris and was amazed to what he saw. It was Niña’s wand.

They were so nervous to see it. The two deep breathily. Besides the wand was a book. They read it and was very curious on how to use the wand. Peter read the book out loud. “How to make a new Creation.” Eris hold his deep breath. His hand was shaking as he hold the magical wand and pointed it the left side. The two were shocked to see the garden became a fruit in just a single glance.

Eris and Peter were excited to try it again. Peter try it this time pointing to different direction and was amazed to see a bridged formed in the lake. Peter was sweating and could barely heard the fast beating and dribbling of his heart. The two were not contented as they fight on holding the wand. “It’s my turn now.” Said Eris. “No” Shouted Peter. They were fighting on the magical wand when it was thrown away hardly by Eris near the Lake. Suddenly the wind blew very strong and there was a lightning

There was a light, slightly translucent around the edges. The two can’t understand what they saw. The light fade away and they saw a creature they had never seen before. It’s not just one but two. One was with long hair like their master and the other was masculine. It doesn’t have feathers or horn nor claws. It has only two feet and has five fingers each. ‘’It’s a human being!’’. Whispered Eris. “Don’t be afraid” said a very cold voice of a woman. It talks like their master. They were the first human being!

The two Human stand up and get the magical wand. Eris and Peter are just watching in the bushes. When suddenly, a big voice was heard, “Give me back my wand!” The two were horrified. It was Niña … Niña was very furious and the wind starts to blow. The man suddenly face the magical wand to Nina’s direction.

“Noooo!” Niña Shouted. A strong hurricane came and flew Niña away. Niña was lure into the hurricane and was trapped away and was sent to the deepest depths of the ocean. It was the end of Niña’s cruelness

It was a new and wonderful start for there was light and no longer was darkness, most importantly there human being to take good care of the world. Eris and Peter led the magical forest again, a more vibrant prosperous place to live with. A world that once became so dark is now becoming more colorful again proving that goodness always prevail over evil.

The End