‘Once in a Blue Moon’ typically means rare or absurd. This year, it means the end of July. The second full moon of July occurs on Friday. According to modern folklore, it’s a “Blue Moon.”
The early definition of the blue moon, as per The Maine Farmer’s Almanac, is the appearance of the third of four full moons in a season. But in the modern description, a blue moon pertains to the second full moon that appears in a single calendar month. Whatever the true definition is, “once in a blue moon” is used to mean “rare.”
In general, there is only one full moon in each calendar month or within a span of 30 days. This means that a blue moon is highly emphasized if the first full moon happened during the first 1-2 days of the month and the second full moon reappears after 30 days, which is still within the same month. The last full moon happened in July 2, making the July 31st full moon appearance as a “blue moon.” Blue moons appear once every 2-3 years and if the modern definition is to be consulted, the last blue moon happened on Aug. 31, 2012.
But the real question here is, “Is it really blue?” The experts think not. The date, period and time interval between the appearances of full moons do not have an effect on the color that the lunar object is likely to showcase. But why choose the color blue among all the other colors available in the spectrum?
According to early literature, people used to see moons that were indeed color blue in 1883. These moons were not specifically full; crescent or half-moons also exhibited the said color, making it a daily sight, except on rare occasions when it turns green. The main reason for this is the eruption of the Krakatoa volcano in Indonesia. The experts compared the said volcanic action to a 100-megaton nuclear bomb explosion.
People from nearly 400 miles were able to hear the eruption, ashes enveloped the sky massively and yes, the moon turned blue. The ashes contained particles that were able to scatter red light immensely and allow other colors to pass. The air had increased amounts of these particles that it turned the moon blue. For a bluer emphasis, the particles must be a little bit wider than the wavelength of red light. The white moonbeams glistening through the atmosphere turned blue and occasionally green.
Although numerous definitions of “blue moon” have emerged, it all points out to one thing: a blue moon is indeed rare and with its reported appearance at the end of the month, people could have another reason to look up in the sky as a new month begins.