If I sound like a curmudgeon, it may be because it’s a stormy Friday with unrelenting cold and cloud and ice pellets falling from the sky. Weather and light both affect mood. I can’t really complain, however. There are places in Australia and New Zealand where the sky is red with ash. For those of you farther away and with clear skies, you may have noticed that the Sunsets recently have been truly spectacular, with deeper reds then we’re used to. 

What you’re seeing is an effect called Rayleigh Scattering. As light passes through any material, whether it be a gas nebula, our atmosphere, or just a cloudy fish tank, the light passing through the material has two options – it can head straight through, or it can get scattered through interactions with the material. While every photon of light has the potential to pass through or be scattered, the probabilities vary with color. Red light is much more likely to pass through than blue light. Astronomically, this causes us to see nebulae lit from behind as red, and nebula lit from the side – reflection nebulae – as blue. In our day to day lives, this is why a cloudy fishtank lit from the top will appear slightly blue, and this is why the light through smoke is red. There have been some tweets out there basically saying the sky is red with reflected fire. While that may sometimes be the case, the same way clouds at night appear orange from sodium lights in cities, the reality is that sunlight passing through smoke clouds turns the day red by scattering out the blue light to the sides.

The same is true of ash from volcanoes, and right now, the combined particles from the Australian fires and Tael Volcano in the Philippines are spreading through out the world’s atmosphere and causing amazing sunsets, a more golden hue in general, and for many difficulty in breathing. 

Some folks have asked if these particles can help drop the Earth’s temperature, and combat climate change. While short term effects from volcanoes have been seen, these are temporary effects that don’t change the problem that we have too many greenhouse gasses in our atmosphere and being released into our atmosphere. Any temporary changes will be reversed as the particles settle out of the atmosphere, and we will be left with a world that has fewer forests. 

Today, these are literally darker times, as we get less light. Tomorrow, or more like several months from now, things we continue to settle into a new normal that will include new and more massive fires, and the normal punctuation of volcanic eruptions. 

More on the background:

• Rayleigh Scattering Sunsets (Physics Central)
• Q&A: How Climate Change, Other Factors Stoke Australia Fires (VOA News)