Blue Skies, Red Sunsets and a Red Moon
I have been impressing a new girlfriend with my knowledge of the night sky. “Why is the Sky Blue?” she asked. Halfway through my explanation Margaret stopped me; “You’re making it up!” rang her accusation. Caught red-handed, and red faced I confessed, but promised to find out;
Blue Skies
Light from the Sun contains all the colours of the rainbow. However to reach us on earth it has to go through our atmosphere. The shorter blue wavelengths of light are the perfect size to interact with the main components of air – oxygen and nitrogen.
So although every colour is being reflected in the air, the majority of collisions are with oxygen and nitrogen particles, meaning that we see a blue sky. This was discovered by Lord Rayleigh, and if you really want to impress YOUR girlfriend, the technical term for a blue sky is Rayleigh Scattering.
Red Sunsets
There is a lot more in the atmosphere than just air. There’s sand from sandstorms, volcanic ash from volcanos, dust, water and man-made pollution. We can bunch all this together and simply call them particles. It’s these particles that can affect other colours.
When the sun is high above, it has a relatively short amount of air to travel through, and Rayleigh Scattering favours short wave-length colours – hence the blue sky. However as the sun gets lower, its light has to travel through more and more atmosphere before it reaches our eyes. This means that its light collides with far more particles in the atmosphere.
If there are plenty of particles in the air, maybe after a long dry period, almost all of the blue can be scattered away. Long wavelengths however will still reach you, and long wavelengths are red in colour. Hence red sunsets - which are more frequent in dry, hot countries.
Red Moons
Sunlight reflected by the moon behaves in exactly the same way, so when it’s low down on a hot dry day, you may see a red Moon.
I hope you understand this now, (I think I do)!
Marathon Runner, Drinker and Artist, Blogging for Pleasure and Profit.
Hi John,
It all makes sense, but I’ll never remember it…lol, so back to making it up.
I really like the pictures…very cool
Cheers
Steve
Glad you like the pictures Steve.....I agree with you, making stuff up is usually much more entertaining.
John[Reply]
Excellent, John, thanks for this. I did know about red sunsets, about the only bit I did know though!
Enjoy the journey.
Mandy
I used to know about this Mandy, and only found out I'd forgotten it all, when I tried to explain it. I suppose this new knowledge might last another 10 years before I have to look it up again.
John[Reply]
Hey John,
Great pictures – the red sunset one is AMAZING – did you use some type of filter on the camera to take it?
Thanks
Thank you!
Jason O’Leary
Webmaster: Candy Direct
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John McNally
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August 18th, 2011 at 2:42 pm
It’s not my photo Jason, I found it on Google.
John
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Well, thank you John, we live and learn. Having failed three GCE’s in the sciences I am hardly the one to question what you say, and you don’t come across as a politician so I assume you tell the truth. I did assume that red skies had something to do with my love of red wine and my short sightedness, but your explanation does sound convincing.
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John McNally
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August 18th, 2011 at 2:45 pm
Red wine will help you appreciate a sunset Roy, but it’s not the reason the sky is red. Thanks for dropping by, I hope you call again.
John
Leamington Spa, England
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Fascinating stuff – now, if you could just explain “red sky at night….” :0)
Thanks!
Carol´s last [type] ..Temple Grandin opening in Boulder
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John McNally
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September 10th, 2011 at 5:08 pm
That’s another blog post Carol, I think it’s dust in the sky but I need further research.
John
Leamington Spa, England
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I really like the red sun set. The angle is just enough to focus the redness of the sunrise. I also like your other photos. You really have the skills in photography.
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John McNally
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September 10th, 2011 at 5:09 pm
Unfortunately I can’t claim credit for the photos Debbie, I found them on Google Images.
John
Leamington Spa, England
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Very nice way to start a very good article! Haha Thanks for sharing the information above since I’m also into photography as a hobby. At least I can share some information to my shoot mates just by reading your article!
Kudos!
More power!
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John McNally
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September 16th, 2011 at 1:06 pm
Thanks for visiting Martin, I’m glad you enjoyed this post.
John
Leamington Spa, England
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Nice way of trying to impress your girlfriend. The information you have given explains a lot. Thank you for the information and you chose nice pictures.
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John McNally
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September 16th, 2011 at 1:08 pm
Thanks Mitch, Google Images helped me find the photos.
John
Leamington Spa, England
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Thanks for clearing that up a little more for me. That explains a little why on days when there are forest fires, there are red sunsets and moon rises. I appreciate the article, thanks again John.
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John McNally
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October 16th, 2011 at 9:04 pm
Glad to have been of help Kent. As you said forest fires could produce red sunsets due to all the ash particles in the air.
John
Leamington Spa, England
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