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Colourful Weather, Ep 3: Why sunsets and sunrises will never be blue or green
Subjects: Geography, Science
Years: 5–6, 9–10
Can you guess how many sunsets and sunrises an astronaut on the International Space Station sees every 24 hours?
Sixteen! Imagine seeing all those spectacular colours so many times a day (even if the view lasts only a few seconds as they zoom by).
Find out exactly why sunrises and sunsets are red, orange and golden but never blue or green, and discover what makes the sky look blue and the sun look yellow.
Produced by the ABC in partnership with the Bureau of Meteorology.
Date of broadcast: 4 Sep 2019
Metadata © Australian Broadcasting Corporation 2020 (except where otherwise indicated).
Digital content © Australian Broadcasting Corporation (except where otherwise indicated).
Video © Australian Broadcasting Corporation (except where otherwise indicated). All images copyright their respective owners.
Text © Australian Broadcasting Corporation and the Bureau of Meteorology.
What's red, gold and orange, fills the sky, and happens every day without fail? Sunrise and sunset. At the start and end of every day, the sky gives us a pretty special light show. Where do these colours come from though, and why only at the start and at the end of the day? To really understand, we need to get back to basics. Sunlight.
Sunlight looks bright and clear, but it's actually made of multiple colours called the colour spectrum and they combine to make white light.
You've seen a rainbow, right? Well, a rainbow is the visible colours of the spectrum all separated out.
Each colour in the spectrum has a different wavelength. Some light travels in short waves, other light travels in long waves.
Light travels from the Sun all the way to the Earth. And on the way, just the last little part of its journey, it has to travel through the Earth's atmosphere.
The atmosphere we live in called the tropospehere, is made up of two particles, oxygen and nitrogen, as well as other molecules like water vapour.
When sunlight hits these molecules, it bounces off them and gets scattered in all directions. It's called rayleigh scattering.
The scattering is what makes the sky look blue.
The only part of the Sun's rays that reach your eyes, because they aren't scattered as much, are the yellows and oranges. That's why in the middle of the day, the sun looks golden. If you looked at it from outer space, though, it would look white. At sunrise and sunset, the Sun is closer to the horizon. That means that the light has to travel through a greater distance of atmosphere than when the Sun is right overhead. That longer distance means that even more of the blue light is scattered away, so that red, orange, and yellow colours that are left intensify. And that's why sunrise and sunsets are beautiful golden orange and red.
You would've seen some pretty spectacular sunrises and sunsets where it looks like the sky is on fire and the colours are extra vivid. Well, how does that happen? The best way is for the air to be fairly clear for brightly coloured sunrises and sunsets. So after it, rains is usually a really great time to get the camera out. It also helps if there is low humidity and some clouds for the light to reflect on.
While we only see one sunrise and sunset a day, astronauts on the International Space Station, zoom around the earth every 92 minutes. Can you guess how many sunrises and sunsets they see in a day? 16! 16 sunrises and 16 sunsets, all clear and bright from out in space where there's no dust smoke or pollution. Except for one little problem. The Space Station travels so quickly, you only get a few seconds to take a look before you zoom past. So I don't know, maybe just one a day is fine when you've got a bit more time to sit back and enjoy the view.