You will see a blue moon on this New Year’s Eve

If you can take a break from all that New Year’s Eve revelry on Thursday, take a look up in the sky. A second full moon in a calendar month will appear in the night sky, an occurrence known as a blue moon.

A blue moon comes every two-and-a-half years on average, but this will be the first time since 1990 that it will coincide with New Year’s Eve. The event will not happen again till 2028. “While everyone’s celebrating they should also take a moment and look up into the night sky,” the Sydney Morning Herald quoted astronomer David Reneke, who is associated with the Australasian Science magazine, as saying. Instead of turning blue, Reneke said, the moon, if anything, could turn red when viewed from cities because of the filter effect of fireworks smoke. So, he said, the best way to view the moon in its pristine state was to get away from the city lights.

But, Reneke said, the eruption in 1883 of the Krakatoa—a volcanic island in the Sunda Strait between the islands of Java and Sumatra in Indonesia—spilled so much dust into the atmosphere that for two years afterwards, the moon took on a bluish hue.

‘Blue moon’ has become a metaphor for a rare event, as encapsulated in the phrase ‘once in a blue moon’. The earliest record of the expression dates back to 1528. A pamphlet criticising the English clergy read: “If they say the moon is blue, we must believe that it is true.” Another interpretation suggests ‘blue moon’ originates from the English meaning of ‘belewe’—which can mean ‘colour’ or ‘betrayer’.