OK, Just a couple of more things on blue moon. “Once in a blue moon,” meaning rarely, has been a well known idiomatic expression since the mid to late 19th century. It’s original meaning of ‘never’ somehow morphed in ‘rarely.’ One possible explanation points to the natural philosopher. The 1800s were a time when science started to answer questions about the physical world, and that knowledge made its way to the public through increasingly easier access to newspaper and books. Common knowledge changes language.
One notable event that naturalists studied and reported on was the eruption of Krakatoa, an Indonesian volcano in the Sundra Straits, near Java. The cataclysmic eruption, late August of 1883, killed somewhere between 36,000 (official toll) and 120,000 people. A massive plume of ash was ejected into the atmosphere. Dark times, indeed. Average global temperatures fell 2.5° F the following year. There were widespread reports of ‘green’ sunsets and ‘blue’ moons over the next several years. And what’s that about? Particulate matter of about one micrometer (as from this eruption) suspended high in the atmosphere will filter out red light, and pass blue. Thus, the blue moon. The same effect has been observed following large forest fires.
I think I’ll let the blue moon thing rest for now, although I reserve the right to look at the 1934 Rogers and Hart lyrics to ‘Blue Moon.’ As well as the subsequent Elvis interpretation. And to report back on a certain Belgian Style beer.