Blood Moon
Blood Moon

When you can see a once-in-a-lifetime lunar trifecta

WHAT happens when a blue moon, a blood moon and a supermoon all converge on the same night? A once-in-a-lifetime lunar trifecta.

Southern Cross University geographer Professor Bill Boyd said the extremely unusual occurrence, due on January 31, is the first 'super red blue moon' for at least 150 years.

"The title 'super red blue moon' sounds a bit peculiar, but it describes an event where three separate lunar conditions come together simultaneously," said Professor Boyd, from the School of Environment, Science and Engineering at Southern Cross University.

"Each happens on its own time cycle, but this year they all happen at the same time.

"This is an extremely unusual occurrence - it will be unlikely for all three celestial events to converge again within the next century."

"A supermoon happens when the moon is at the closest point on its orbit around the Earth, some 25,000km closer than on average. It appears 14 per cent larger than usual and 30 per cent brighter.

This happens every 14 months or so," Professor Boyd said.

"Meanwhile, a lunar eclipse happens when the sun, the Earth and the moon are completely aligned, so that the moon travels through the Earth's shadow. It occurs two to four times a year, though not usually a full eclipse.

"Indeed, the January 31 lunar eclipse is the first total eclipse in 150 years."

Professor Boyd said as the moon passes through the earth's shadow, people often assume it will go completely dark.
However, some of the sunlight entering the Earth's atmosphere, notably the red spectrum, is scattered in a way that gently illuminates the moon.

"This gives the moon its red glow and is often referred to as a red or blood moon," he said.

"As for the blue moon, it's not actually blue! It is a name now used to describe a second full moon in a month."

He said there is confusion around the meaning of 'blue moon'.

The term used to describe a fourth full moon in a season - which normally has three. It now describes the second full moon in a calendar month which happens about every 2.7 years.

In a rare set of circumstances, a second blue moon in two months will rise at the end of March this year, which follows on from a series of three supermoons over the Australian summer.

Professor Boyd confirmed that the supermoon is associated with higher-than-usual tides, but said they are not the only control over high tides.

"There have been especially high tides worldwide recently. These are linked to the supermoon, but also caused by the peak of an 18.6-year cycle of the moon … just another interesting convergence of lunar events," he said.

However, Professor Boyd emphasised that, despite what some might believe, the moon doesn't cause natural disasters.

"I'm not an astrophysist or astronomer, but as a geographer I take a keen interest in these natural earthly phenomena," he said. "There is no link between the moon and geological events such as tsunamis and earthquakes.

These geological processes do not need the moon to do anything. They happen for entirely different earthly causes."

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