Blue moons happen more often than you might think. Photo: Fairfax
ONCE in a blue moon happens more often than you might think, or at least it does in astronomical circles.
Normally people would use that expression if they’re talking about something rare, silly, or even absurd.
Rare or not, we’re having one tomorrow, says astronomer David Reneke, writer and publicist for Australasian Science magazine.
Mr Reneke said he wasn’t sure where the term originated, but in modern folklore it goes back at least 400 years.
“A blue moon is the second full moon in a calendar month,” Mr Reneke said.
“Usually months have only one full moon, but occasionally a second one sneaks in. Ancient cultures around the world considered the second full moon to be spiritually significant,”
Full moons are separated by 29 days, while most months are 30 or 31 days long, so it is possible to fit two full moons in a single month, with the only exception being February. “A blue moon happens every two-and- a-half years, on average. We had a full moon on August 2 this year and the second will be on Friday night,” he said.
Just in case you’re wondering, the moon doesn’t actually turn blue, but there are occasions when pollution in the Earth’s atmosphere can make the moon appear to be a shade of blue.
“The moon appeared bluish-green across the entire Earth for about two years after the eruption of Krakatoa in 1883 and there were reports of a blue-green coloured moon caused by Mt St Helens in 1980 and Mount Pinatubo in 1991, so in a sneaky sort of way, it could be true,” Mr Reneke said.
When the sun sets in the west, the full moon rises, so look skyward at sunset tomorrow and perhaps spare a thought for the man who first walked on the moon in July, 1969 – Neil Armstrong, who passed away earlier this week.