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Look Up, A Rare Blue Moon Will Light Up The Sky This Halloween For The First Time In 19 Years

By Rick Stephens
24th Sep 2020

A whitish-blue moon in the mostly clear early evening sky.

2020 has been a peculiar year. In March, Uranus started leaking gas (literally), a bird called the Aldabra rail re-evolved itself back into existence, and back in January Poland accidentally invaded the Czech Republic. And now, this year is throwing one more into the mix—a blue moon on Halloween.

The phenomena, however, doesn’t do exactly what it says on the tin. While the moon will be full on Halloween, it won’t necessarily be blue. Confused yet? Let Sydney PhD student, Joshua Pritchard, who studies in the area of radio astronomy, break it down for you.

“A blue moon is what we call the second full moon in a calendar month. The moon takes 29 and a half days to orbit the Earth and return to the same position in the sky. From our perspective on Earth, we see this motion as the changing lunar phases; with the new moon beginning when the sun and moon are closest to one another in the sky, then building up to a full moon over about two weeks, and finally waning over another two weeks back to a new moon.

“This is totally separate to the moon actually looking blue, which can sometimes happen with the right amount of smoke in the air,” says Pritchard.

If you’re the type to employ a smoke machine into your festivities on Saturday 31 October, you might score yourself a blue moon after all, but Pritchard explains there’s another—more pragmatic—reason why this blue moon is so rare.

“It actually happens on a sort of repetitive cycle of about 19 years. If you pick any particular day of the year, the phase of the moon will be roughly the same 19 years later.”

For those hoping to cash in on October’s second full moon this Halloween, Pritchard has several tips in getting bang-for-your-buck.

“The moon looks most impressive when it is rising or setting so that you catch it framed by other features of the horizon. 

“If you've been stuck inside a lot lately and have missed our nearest neighbour, it's a good excuse to stake out your favourite view of the ocean or landscape. It will rise at the same time the sun is setting, so two-for-one.” Pritchard said.

Anyone hoping to catch the sun setting and the blue moon rising should keep an eye on the skies around 7:30pm on Saturday 31 October.

Find a prime position with Australia’s best stargazing spots.

Image credit: Marcus Dal

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