Simple answer – if you can predict the weather, you can predict the factors necessary to determine if a sunset will be a beautiful red one or not.  Already I can feel people shutting this post down knowing how hard it is to get a weather prediction, but stick with me. I’m going to try and explain, in as simple a way as possible, what causes those beautiful, fiery sunsets and, as a result, how you can make sure you’re out there with your camera to take an amazing photo that you can subsequently oversaturate and get you all the votes you ever need on 500px.

Prediction Tools

First up, if you live in the continental USA and you have The Photographer’s Ephemeris then check out the Skyfire app – it will provide a heatmap of where the ‘best’ light will be for your sunset shoots.  The rest of us will need to do our best to work it out for ourselves, but it is possible!

The basics…why does sun colour change

In researching this post I realised how complex it is to actually answer this question.  If you want to learn more, there are heaps of great physics and meteorology papers out there that you can research (I’ve linked a few goodies at the bottom of this post).  But, in layperson’s terms, light isn’t a single colour, but it’s made up of multiple wavelengths.  As the light passes through our atmosphere some of these wavelengths hit the molecules in our atmosphere and and ‘scatter’.  The longer light passes through out atmosphere the more the light ‘scatters’ – the blue wavelengths are the first to scatter while the red ones hang around.  So, when light passes through our atmosphere, unobstructed, at midday it spends a relatively short time being ‘scattered’ so we see a lot of blue, hence the blue sky.  However, at sunset, the light from the sun takes a shallower angle and it takes relatively longer for the light to reach us – this leads to more of the light wavelengths scattering and what we see is just the red wavelengths left over.

The best way to describe this is pictorially.  This is the point where my followers realise how little Photoshopping goes into my photos because, as you can see, I have not artistic skills.  My high school art teacher actually told my parents not to waste any money on buying me art supplies 🙂

Figure 1: Unobstructed Sunset

Figure 1: Unobstructed Light Leaving a Reddish Sunset

 

As you can see in Figure 1, the longer light spends in our atmosphere the more of the blue wavelengths are scattered and the more likely you are to see the awesome red colours.  BUT, this only really happens when you have an unobstructed view.  If there’s loads of cloud cover in the West (where the sun sets!) then you get less light coming to you at sunset, leaving the dull colouration, as you can see in Figure 2.

 

Figure 2: Obstructed Light

Figure 2: Clouds to the West obstructing the sunlight and leaving a dull sunset

Clouds

But, don’t fret.  Just because it’s cloudy, doesn’t mean it won’t be an awesome sunset.  Indeed, having clouds gives you the most interesting colours.  The clouds themselves don’t create any light, but they do act like a refractor reflector (thanks Andrew Caldwell!) of the light, meaning we get a more interesting scene.  The types of clouds do matter – thick and low clouds means that not enough light will get to you.  So some nice high clouds offer a great canvas to reflect red light off.

Boat on the Water

Boat on the Water

Selfie (well, actually me wondering why I’m standing in the river without a rod)

Clouds also offer you the chance to see some other cool effects, like crepuscular and anti-crepuscular rays (the beautiful rays of light that come from some of the sun’s light being obstructed – too much and you get murky colouration, but when a little light shines through you get some awesome rays).

Anti-crepuscular rays over Lyttelton Harbour

Anti-crepuscular rays over Lyttelton Harbour

 

Moisture in the atmosphere

Too much moisture usually means more water molecules for light to obstruct your light meaning duller colours.  Loads of moisture means low thick clouds, which is even worse.  If the air is dry, you’ve got a better chance for a good sunset.

 Nor-West winds in Canterbury give a dry hot air that leaves a spectacular sunset


The dry winds in Canterbury can give a spectacular yellow/red sunset

Haze and Pollution

I always believed that pollution gave you lovely colours.  This is not true, apparently.  Pollution acts like other molecules in the air and just obstruct light, giving you a duller effect.  This is not to say that haze can’t add to your photos (especially when you’ve got some cool sun rays), but generally it’s best to find clean air.

Clean, dry air will give you more vibrant colours at both sunrise and sunset

Clean, dry air will give you more vibrant colours at both sunrise and sunset

 

Best conditions for a fiery sunset

In summary, the best sunsets come from the following:

  • Clean, dry air.
    • Warm days mean less water molecules to dull your light, making for good sunsets (hence the amazing sunsets in the desert)
  • Unobstructed weather to the West.
    • Look West and check out the cloud action.  If the horizon is clear, it’s a good sign that the sunlight will reach your location.
  • High clouds over your location.
    • This will give you the best shot at some sweet reflections off the sky as the colours change.
  • Luck.
    • You can plan and predict but some nights are just better than others.  Even though I’ve provided 3 key variables above, they are infinitely complex and almost impossible to get 100% correct.  However, since learning about this I’ve been able to generally predict which sunsets will be better than others, saving me a lot of time, heartache and petrol driving out to take shots that turn out to be boring, flat light.  Of course, you can just photoshop the hell out of your photos and claim it as being a beautiful sunset – now one will know!

So, what do you think? Ready to predict a fiery sunset? If I’ve missed something or messed something up, let me know!

 

Further reading

If you’re keen to get into the details of what I’ve written here, here are some good posts that give more info for you.  Enjoy!

Optics for Kids Explanation – Great for teaching your kids about light (ok, and for adults who have science ability of kids, like me)

Interview with Stephen Corfidi, a National Oceanic and Atmospheric Administration meteorologist by National Geographic (my favourite link here – really informative, but simply explained).

More from Stephen Corfidi talking about the colours of twilight (has some good pics to explain his work in the area and a solid reference list to check out).

Universe Today’s “Why is the Sunset Red?” post that offers a little more detail about the light wavelengths

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