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How to predict a good sunrise or sunset so you can brag about it on social media

Kate Doyle, Friday May 11, 2018 - 06:26 EST
ABC image
Marc Best captured this shot of glorious skies over Mt Wellington in February. - ABC

It is nature's nightly show — the first hints of pink that creep across the sky and develop into a riot of deepest oranges and reds if you are lucky.

You are even luckier if you have your camera out and can brag about it on social media.

As part of the ABC's focus on weather we have started the a place where you can discuss weather issues, share pictures and ask questions.

And Michelle Milikins from Mackay wanted to know: Can you ever predict when there will be a good sunset or sunrise?

That is not the kind of challenge we take lightly at Weather Obsessed!



But first, why are sunsets coloured in the first place?

Monash University astronomer Duane Hamacher has several degrees in astrophysics, and his work explores the connections between culture and the skies.

He said the sky's colour was the result of a process called Rayleigh scattering, an effect from quantum mechanics.

When light from the sun enters the Earth's atmosphere, the blue wavelengths of light get scattered, but the red wavelengths of light do not.



So during the day, when the light only has to travel a short distance through the atmosphere, we see the blue scattered light and the sky looks blue.

"[But] when the sun is low on the horizon, like at sunrise or sunset, the light coming through is reddened," Dr Hamacher said.

So all the blue light gets scattered but the red light comes through, and we get to see all the longer wavelength reds and oranges painted across the sky.

What makes one sunrise better than another?

Ann Britton lives on a beef-growing property just outside of Boulia, 300 kilometres south of Mt Isa, and she takes beautiful sunset and sunrise photos.

Ms Britton said the key to a spectacular sunset was a touch of cloud.

"Most mornings I look and see is there going to be any cloud?" she said.



"I think every sunrise is pretty special. Even if there's no cloud, it's still very special to be able to see the sunrise.

"But I usually look at it and see if there's any cloud about and what the atmospheric conditions are, whether there's a bit of cold there or not and I go from there."

So having clouds and colour are important when trying to predict a good sunset, but what else do we need to know?

Can sunsets be used to predict the weather?

You may have heard of the saying, "Red sky at night sailor's delight. Red in the morning, sailor's warning."

Some say "shepherd" and some say "fisherman" but they all get at the same thing. References to the saying go all the way back to the Bible, but is it the gospel truth?

Dr Hamacher said the saying's validity varied depending on where the world you were observing the sunrises and sunsets.



The saying does roughly hold though for places such as southern Australia, where the weather generally moves from west to east.



"If you see the really beautiful red sky at sunset, that means whatever bad weather is probably moving away, but if you see that in the morning, that means it's coming towards you," Dr Hamacher said.

He said that along with good colours and clouds, he would also look for clear atmospheric conditions if he was to try and predict a good sunrise or sunset.

"Preferably drier conditions. When there's less humidity in the atmosphere, the light that gets refracted up on the cloud, it's more crisp. It's more clear," Dr Hamacher said.

"You also get really beautiful sunsets after a rainfall … it sort of cleans the air."

How then to predict a speccy sunset?

It should be possible. Clouds, weather patterns, rainfall and humidity can all be forecast.

But it turns out working out exactly which combination creates the ultimate formula for a perfect sunset is a bit tricky.

There are a few sunset prediction websites and apps on the market.



Gregory Dunbar, founder of the sunrise and sunset predictor app SkyCandy, said he took into account:
Humidity — best when humidity is low but not too low.
Cloud coverage — best when between 30 per cent and 70 per cent. Not good if below 30 per cent, and terrible if above 90 per cent.
Prior rainfall — 2–6 hours before sunrise or sunset is okay, but not during sunrise or sunset.
Visibility — the higher the better.
Wind speed — best if the wind speed is low or non-existent.
Fog — no fog … this should go without saying.



These are some of the factors. He was not silly enough to give away the whole story.

SunsetWx, a webpage that does global sunset and sunrise forecasts, has a methodology section — which explains it puts a heavy weighting on atmospheric moisture, without giving away its exact model.

Initial testing suggests these systems are a bit hit and miss, and neither claim to be 100 per cent accurate.

So at Weather Obsessed, .



After all, Ann is right: "It's really nice to share spectacular sunrises and sunset. Some people already appreciate them very much and others don't get the chance to appreciate them. So it's always nice to share something so nice."

It also would be great to know when it is going to be worth getting up early to catch a perfect sunrise.


- ABC

© ABC 2018

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