Look at the night sky and you will see a full moon, the second this month ( the first was August 2). Two full moons in the same month occur just once every 2.5 years or so. QUT astrophysicist Dr Stephen Hughes said we had a full moon on August 2 and the next on August 31, the blue moon, will make two "squeezed" into one month. "Blue Moons occur only about seven times in 19 years—that's about once every two-and-a-half years," Dr Hughes said. "A bit like the leap year, a blue moon happens as a calendar catch-up because it takes the moon about 27 and a half days to go round the earth and since this is less than the number of days in a calendar month, two full moons can sometimes occur in a single month...
Dr Hughes said a blue moon was not coloured blue although the moon could appear blue when there were smoke or volcanic ash particles suspended in the atmosphere. "A blue-tinged moon is a rarity and so maybe that's where the saying came from. There are reports of blue moons after the Krakatoa eruption in Indonesia in 1883 in which volcanic ash was ejected 80km high, on the edge of the ionosphere," he said.
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