Next Blue Moon August 22, 2021
Our last Blue Moon came on October 31, 2020, the night of Halloween. Like most Blue Moons, it was blue in name only. It was called a Blue Moon because it was the second of two full moons in a single month.
There’s another definition for Blue Moon. It can also be the 3rd of four full moons in a single season. A season is the period between a solstice and an equinox. The next Blue Moon will be of this sort, and it’ll happen on August 22, 2021.
In recent years, people have been using the name Blue Moon for these two different sorts of moons: 2nd of two full moons in a calendar month, or 3rd of four full moons in a single season.
Blue-colored moons in photos – like the ones on this page – are usually made using special blue camera filters or in a post-processing program such as PhotoShop. Usually … but not always.
Are moons ever blue in color?
Sure, they are, and someday you might see a true blue-colored moon in the sky.
Blue-colored moons are rare – aren’t necessarily full – and happen when Earth’s atmosphere contains dust or smoke particles of a certain size. The particles must be slightly wider than 900 nanometers.
You might find particles of this size in the air above you when, for example, a wildfire is raging nearby. Particles of this size are very efficient at scattering red light. When these particles are present in our air, and the moon shines through them, the moon may appear blue in color.
For more about truly blue-colored moons, click here.
First, seasonal Blue Moons
.
By season, we’re referring to the period of time between a solstice and an equinox. Or vice versa. We’re talking about winter, spring, summer, fall. Each season typically lasts three months and typically has three full moons. The upcoming seasonal Blue Moon of August 22, 2021 happens because June’s full moon falls just a few days after the June solstice, early in the season of northern summer (southern winter).
And thus there’s enough time to squeeze four full moons into the current season, which will end at the September equinox on September 22, 2021.
Weirdly, it’s not the 4th of these four full moons that’ll be called a Blue Moon. It’s the 3rd. Go figure.
Full moons between June 2021 solstice and September 2021 equinox:
June solstice: June 21, 2021
June full moon: June 24, 2021
July full moon: July 24, 2021
August full moon (a Blue Moon): August 22, 2021
September full moon: September 20, 2021September solstice: September 22, 2021
How often do seasonal Blue Moons happen? Pretty often! There was a seasonal Blue Moon on November 21, 2010, another on August 20-21, 2013, another on May 21, 2016, and another on May 18, 2019. You get the idea.
The upcoming Blue Moon will be on August 22, 2021.
Now, the 2nd full moon in a month
In modern times, most of us know Blue Moons as the 2nd full moon of a single calendar month.
These happen a lot, too! By this definition, there was a Blue Moon on July 31, 2015; January 31, 2018; March 31, 2018; and October 31, 2020.
The time between one full moon and the next is close to the length of a calendar month. So the only time one month can have two full moons is when the first full moon happens in the first few days of the month. This happens every two to three years, so these sorts of Blue Moons come about that often.
Very rarely, a seasonal Blue Moon (3rd of four full moons in one season) and a monthly Blue Moon (2nd of two full moons in one calendar month) can occur in the same calendar year. For this to happen, you need 13 full moons between successive December solstices for a seasonal Blue Moon – and, generally, 13 full moons in one calendar year for a monthly Blue Moon.
This will next happen in the year 2048, when a monthly Blue Moon falls on January 31, and a seasonal Blue Moon on August 23.
Then 19 years later, in the year 2067, there will be a monthly Blue Moon on March 30, and a seasonal Blue Moon on November 20. In this instance, there are 13 full moons between successive December solstices – but only 12 full moons in one calendar year and no February 2067 full moon.
Why call them Blue Moons?
The idea of a Blue Moon as the 2nd full moon in a month is more recent – more modern – than the idea of a Blue Moon as the 3rd of four full moons in a season. It stemmed from the March 1946 issue of Sky and Telescope magazine. The magazine published an article called “Once in a Blue Moon” by James Hugh Pruett. Pruett was referring to the 1937 Maine Farmer’s Almanac, which defined Blue Moons as the 3rd of four full moons in a season. But he inadvertently simplified the definition. He wrote:
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.
Had James Hugh Pruett looked at the actual date of the 1937 Blue Moon, he would have found that it had occurred August 21, 1937. Also, there were only 12 full moons in 1937. You generally need 13 full moons in one calendar year to have two full moons in one calendar month.
However, that fortuitous oversight gave birth to a new and perfectly understandable definition for Blue Moon.
The notion of a Blue Moon as the 2nd full moon of a calendar month was buried for decades. Then, in the late 1970s, EarthSky’s Deborah Byrd happened upon a copy of the old 1946 issue of Sky and Telescope in the stacks of the Peridier Library at the University of Texas Astronomy Department. Afterward, she began using the term Blue Moon to describe the 2nd full moon in a calendar month on the radio series StarDate, which she wrote and produced.
Later, this definition of Blue Moon was also popularized by a book for children by Margot McLoon-Basta and Alice Siegel, called Kids’ World Almanac of Records and Facts, published in New York by World Almanac Publications in 1985. The second-full-moon-in-a-month definition was also used in the board game Trivial Pursuit.
Today, it has become part of modern folklore. As the folklorist Philip Hiscock wrote in his comprehensive article “Once in a Blue Moon“:
‘Old folklore’ it is not, but real folklore it is.
Resources:
Bottom line: Modern folklore has defined two different kinds of Blue Moons. The last Blue Moon – second full moon of a calendar month – came on October 31, 2020. The other sort of Blue Moon – third of four full moons in a single season, with a season being between a solstice and equinox – will come on August 22, 2021.
Possible to have only 2 full moons in a single season?
Enjoying EarthSky so far? Sign up for our free daily newsletter today!
The post What’s a Blue Moon, and when’s the next one? first appeared on EarthSky.
from EarthSky https://ift.tt/3zOLIs8
Next Blue Moon August 22, 2021
Our last Blue Moon came on October 31, 2020, the night of Halloween. Like most Blue Moons, it was blue in name only. It was called a Blue Moon because it was the second of two full moons in a single month.
There’s another definition for Blue Moon. It can also be the 3rd of four full moons in a single season. A season is the period between a solstice and an equinox. The next Blue Moon will be of this sort, and it’ll happen on August 22, 2021.
In recent years, people have been using the name Blue Moon for these two different sorts of moons: 2nd of two full moons in a calendar month, or 3rd of four full moons in a single season.
Blue-colored moons in photos – like the ones on this page – are usually made using special blue camera filters or in a post-processing program such as PhotoShop. Usually … but not always.
Are moons ever blue in color?
Sure, they are, and someday you might see a true blue-colored moon in the sky.
Blue-colored moons are rare – aren’t necessarily full – and happen when Earth’s atmosphere contains dust or smoke particles of a certain size. The particles must be slightly wider than 900 nanometers.
You might find particles of this size in the air above you when, for example, a wildfire is raging nearby. Particles of this size are very efficient at scattering red light. When these particles are present in our air, and the moon shines through them, the moon may appear blue in color.
For more about truly blue-colored moons, click here.
First, seasonal Blue Moons
.
By season, we’re referring to the period of time between a solstice and an equinox. Or vice versa. We’re talking about winter, spring, summer, fall. Each season typically lasts three months and typically has three full moons. The upcoming seasonal Blue Moon of August 22, 2021 happens because June’s full moon falls just a few days after the June solstice, early in the season of northern summer (southern winter).
And thus there’s enough time to squeeze four full moons into the current season, which will end at the September equinox on September 22, 2021.
Weirdly, it’s not the 4th of these four full moons that’ll be called a Blue Moon. It’s the 3rd. Go figure.
Full moons between June 2021 solstice and September 2021 equinox:
June solstice: June 21, 2021
June full moon: June 24, 2021
July full moon: July 24, 2021
August full moon (a Blue Moon): August 22, 2021
September full moon: September 20, 2021September solstice: September 22, 2021
How often do seasonal Blue Moons happen? Pretty often! There was a seasonal Blue Moon on November 21, 2010, another on August 20-21, 2013, another on May 21, 2016, and another on May 18, 2019. You get the idea.
The upcoming Blue Moon will be on August 22, 2021.
Now, the 2nd full moon in a month
In modern times, most of us know Blue Moons as the 2nd full moon of a single calendar month.
These happen a lot, too! By this definition, there was a Blue Moon on July 31, 2015; January 31, 2018; March 31, 2018; and October 31, 2020.
The time between one full moon and the next is close to the length of a calendar month. So the only time one month can have two full moons is when the first full moon happens in the first few days of the month. This happens every two to three years, so these sorts of Blue Moons come about that often.
Very rarely, a seasonal Blue Moon (3rd of four full moons in one season) and a monthly Blue Moon (2nd of two full moons in one calendar month) can occur in the same calendar year. For this to happen, you need 13 full moons between successive December solstices for a seasonal Blue Moon – and, generally, 13 full moons in one calendar year for a monthly Blue Moon.
This will next happen in the year 2048, when a monthly Blue Moon falls on January 31, and a seasonal Blue Moon on August 23.
Then 19 years later, in the year 2067, there will be a monthly Blue Moon on March 30, and a seasonal Blue Moon on November 20. In this instance, there are 13 full moons between successive December solstices – but only 12 full moons in one calendar year and no February 2067 full moon.
Why call them Blue Moons?
The idea of a Blue Moon as the 2nd full moon in a month is more recent – more modern – than the idea of a Blue Moon as the 3rd of four full moons in a season. It stemmed from the March 1946 issue of Sky and Telescope magazine. The magazine published an article called “Once in a Blue Moon” by James Hugh Pruett. Pruett was referring to the 1937 Maine Farmer’s Almanac, which defined Blue Moons as the 3rd of four full moons in a season. But he inadvertently simplified the definition. He wrote:
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.
Had James Hugh Pruett looked at the actual date of the 1937 Blue Moon, he would have found that it had occurred August 21, 1937. Also, there were only 12 full moons in 1937. You generally need 13 full moons in one calendar year to have two full moons in one calendar month.
However, that fortuitous oversight gave birth to a new and perfectly understandable definition for Blue Moon.
The notion of a Blue Moon as the 2nd full moon of a calendar month was buried for decades. Then, in the late 1970s, EarthSky’s Deborah Byrd happened upon a copy of the old 1946 issue of Sky and Telescope in the stacks of the Peridier Library at the University of Texas Astronomy Department. Afterward, she began using the term Blue Moon to describe the 2nd full moon in a calendar month on the radio series StarDate, which she wrote and produced.
Later, this definition of Blue Moon was also popularized by a book for children by Margot McLoon-Basta and Alice Siegel, called Kids’ World Almanac of Records and Facts, published in New York by World Almanac Publications in 1985. The second-full-moon-in-a-month definition was also used in the board game Trivial Pursuit.
Today, it has become part of modern folklore. As the folklorist Philip Hiscock wrote in his comprehensive article “Once in a Blue Moon“:
‘Old folklore’ it is not, but real folklore it is.
Resources:
Bottom line: Modern folklore has defined two different kinds of Blue Moons. The last Blue Moon – second full moon of a calendar month – came on October 31, 2020. The other sort of Blue Moon – third of four full moons in a single season, with a season being between a solstice and equinox – will come on August 22, 2021.
Possible to have only 2 full moons in a single season?
Enjoying EarthSky so far? Sign up for our free daily newsletter today!
The post What’s a Blue Moon, and when’s the next one? first appeared on EarthSky.
from EarthSky https://ift.tt/3zOLIs8
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