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On October 31, Halloween night, we must not only be on the lookout for demons and ghosts. Look up into the sky for something more unusual: a blue moon.
Despite its name, a blue Moon is not, in fact, blue. The modern term refers to a season with four instead of three full moons, or an additional full moon within a calendar month. The interval between two full moons is approximately 29.5 days; Since most months are 30 or 31 days long, another Full Moon may occasionally tighten.
Blue moons are quite rare, occurring roughly every two and a half years. On October 1, the first full moon of the month occurred, the so-called Harvest Moon, which is traditionally the one that is closest to the autumn equinox. The second full moon of the month, on October 31, is known as the Hunter’s Moon.
What makes this month’s blue moon even more unusual is that it is the first time a full moon has fallen on Halloween since 2001, and it won’t happen again until 2039. This is thanks to something called the ‘metonic cycle’, where a phase of the Moon will repeat on the same date every 19 years. This was calculated by the ancient Greek astronomer Meton of Athens, in the 5th century BC. C.
So where does the term ‘a blue moon’ come from? According to Jodrell Bank, the oldest written record that “a blue moon” means something that rarely occurs dates back to 1821. In his work Life in London journalist Pierce Egan wrote about the various characters, culture and language of the London streets and recorded the use of the expression, providing a handy footnote to describe what it meant. There were a few more uses of the term by other authors in later work, which is why it is believed to have originated in London in the 19th century.
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As discussed, the Moon will have its usual non-creepy grayish-white color. But can the Moon really turn blue? Blue-hued moons only tend to occur when there is a lot of smoke, ash, or other particles in the atmosphere. For example, after the massive volcanic eruption of Krakatoa in 1883, huge amounts of ash and airborne particles made the Moon appear blue for months. More recently, a gigantic wildfire in western Canada broke out from June to October 1950. The smoke eventually traveled east across the Atlantic and reached the UK and northern Europe in September, returning the Sun and the Blue moon.
So while the Moon on Halloween may not be blue, it’s still a rare astronomical treat. It will be visible around the world and no special equipment is required to view it (although if you have a pair of binoculars, they will allow you to get a closer look at some of its features). You should take some time to enjoy the view, and it will do a lot less damage to your teeth than the huge bag of pick ‘n’ mix you bought for ‘trick-or-treating’!
Reader Questions and Answers: What would happen if there was no Moon?
Asked by: Derek Palmer, Eton Wick
The most immediate effect (aside from the lack of moonlight, of course) would be on Earth’s tides. With just the gravitational influence of the Sun, the difference between high and low tides would be drastically reduced, as would tidal drag, which slows the Earth down to a speed that adds about 0.002 seconds to the duration of a day every century. In the long term, the effects would be much more serious.
The climate of the Earth depends significantly on the inclination of 23.5 ° of the Earth’s axis, and without the stabilizing presence of our relatively large Moon, the gravity of the other planets would produce large changes in this angle, as occurs with Mars, of which the inclination changes by 60 ° over a few million years.
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