Rare blue moon: When will it rise and how to watch the majestic phenomenon

A rare seasonal sight will grace US skies soon, based on the original definition of 'blue moon' and not the 1946 misinterpretation we use today

                            Rare blue moon: When will it rise and how to watch the majestic phenomenon
A partially eclipsed super blue blood moon sets behind the Golden Gate Bridge on January 31, 2018, in San Francisco, California (Justin Sullivan/Getty Images)

On August 22, the US skies will witness a seasonal, but still rare, astronomical phenomenon - a blue moon. This is the first seasonal blue moon since the one we witnessed in October 2020, perhaps aptly on Halloween day. Miss this, and the next one is scheduled only for Aug. 19, 2024, followed by May 20, 2027. It's a good way to take a break from the stress of work, and of course Covid-19.

Astronomical phenomenon, like the blue moon, is certainly a sight to behold, not just for avid astronomers, but anyone in general. In December, we were able to witness the Geminid Meteor Shower around the world. So far this year, we've been treated to the annual Lyrid Meteor Shower on Earth Day, and a pink moon on April 26. Now, we are going to witness the first blue moon of 2021.


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Now before you get all excited, you should know that the moon won't actually be blue. It'll just be its regular gray self. The term can often be confusing, and in fact, that confusion is what is responsible for the event we are about to witness. But don't worry, we will clear it up for you. Here's why this weekend's moon will be "blue", and how you can see it.

A Super Blue Blood Moon rises above Portsmouth on January 31, 2018, in Portsmouth, United Kingdom. (Matt Cardy/Getty Images)


What is a blue moon?

There are two reasons for a blue moon. The first is the literal meaning when the moon appears blue. That is because of atmospheric pollution like volcanic dust or soot from forest fires. Such instances occurred after the eruption of the Krakatoa volcano in August 1883, or the western Canada forest fires in September 1950. Even though California is witnessing massive forest fires, don't expect the moon to appear blue on August 22. That brings us to the second reason.

Normally, we see 12 full moons each year and three per season. That rule emerged from the now-defunct Maine Farmer's Almanac. In 1937, the almanac said, "there will come a year when there are 13 full moons, not the usual 12." The almanac dubbed the third moon of the season as the "blue moon" so that the fourth could be called a late moon when it appeared. That was done so as to avoid using the number 13, which as you well know is considered unlucky. 



Now, here's where things get really interesting. In 1946, the Oregon-based astronomer James Hugh Pruett misinterpreted the Almanac's definition. In an article for Sky and Telescope, 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." That definition was widely accepted, and the original one by the Farmer's Almanac was forgotten.

As a result, the term blue moon today is often used for the second full moon in a month, but that's not what we will see on August 22. What we will witness on Sunday will be the original blue moon, as described by the Maine Farmer's Almanac, i.e. the third full moon this season. So you don't get confused, think of this phenomenon as the seasonal blue moon, while Pruett's definition is the calendrical blue moon.

A fully eclipsed super blue blood moon sets behind Coit Tower on January 31, 2018, in San Francisco, California. (Justin Sullivan/Getty Images)


How to witness the blue moon?

The seasonal blue moon is considered a very rare sighting because it only occurs about once every 2.7 years. That's why you shouldn't miss it. The moon will be at its peak on August 22 at 8.02 am Eastern time. Of course, you can see it much before that. The moon will be visible from Saturday, August 21 till August 22. So step outside some time after 9.00 pm Eastern time on August 21, and you should be able to spot this rare phenomenon.

You should be able to spot the moon with your naked eye, no fancy equipment is needed! If you live in a dense or polluted part of the city, why not make a trip to a remote or high point? Pack your dinner and make it a night out with friends and family, giving you a great chance to witness something truly unique. If you plan to visit a national park, know that the National Park Service has instituted a mask mandate "inside all NPS buildings and in crowded outdoor spaces, regardless of vaccination status or community transmission levels."

If you are interested, the blue moon we are about to witness is also sometimes called the Green Corn Moon, the Grain Moon, and the Sturgeon Moon. It is linked to the fact that this phenomenon usually heralds the coming of the harvest season. 

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