CrowdScience

Why isn't the sky green?

Feb 21, 2025

Explore the enchanting hues of the sky, from vibrant sunsets to the surprising science behind color perception. Discover why we see blue during the day and the rare occurrences when green appears, like in a rainbow or the elusive green flash. Delve into the role of sunlight scattering and how our brains interpret these colors. Journey to the Arctic to witness the mesmerizing northern lights and learn how solar particles create stunning auroras. This fascinating investigation uncovers the beauty and complexity of what paints our sky.

27:02

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Quick takeaways

The sky predominantly appears blue due to the scattering of shorter wavelengths of light, while longer wavelengths dominate during sunsets.

Green is rarely visible in the sky, but can occasionally be observed during phenomena like auroras and rainbows.

Deep dives

The Elusiveness of Green in the Sky

Green is a rare color in the sky, particularly during sunset and sunrise. As light passes through the atmosphere at low angles, shorter wavelengths of blue and violet light scatter away, leaving longer wavelengths of red and orange to dominate. This leaves green light in an 'unlucky' middle position where it doesn't scatter efficiently enough to make a significant visual impact. Essentially, while some green light is present during these times, it gets overshadowed by the reds and yellows, rendering it nearly invisible to the human eye.

Intro

5min

The Science Behind Sky Colors: From Blue to Sunset Hues

4min

Understanding the Mind's Color Perception

2min

Understanding Color Perception Through Photoreceptors

2min

The Science of Color: Sky Phenomena and Perception

15min

Vermillion red, vibrant orange, golden yellows, even violet – we're enchanted by the colours that make up a stunning sunset or sunrise. CrowdScience listener Paulina, a lighting designer from Chile, often uses the sunsets she sees from her balcony as inspiration for her designs. And during the day and night, the sky can be all sorts of shades of blue. But Paulina wonders why, in the colour palette of the sky, she never sees any green.

CrowdScience gazes skywards to investigate. Presenter Caroline Steel travels to the Arctic Circle to meet atmospheric physicist Katie Herlingshaw. Katie explains why we usually see the sky as blue, and what makes it transform into fiery reds and oranges at sunrise and sunset. We also peer into the science of perception, as neuroscientist Bevil Conway tells us what’s going on in our eyes (and brains) to make the colours we see in the sky.

But there are some rare occasions when the sky can appear to be green, such as in a rainbow or a green flash at sunset. And then there is the spellbinding green glow of the aurora - the Northern and Southern Lights. We visit the northernmost aurora observatory in the world to try to understand this phenomenon. Are green skies more common than we think?

Presenter: Caroline Steel Producer: Hannah Fisher Editor: Cathy Edwards Production Co-ordinator: Ishmael Soriano Studio Manager: Sarah Hockley

(Photo: View of sunset in Santiago, Chile. Photo montage courtesy of Paulina Villalobos)

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CrowdScience

Why isn't the sky green?

Podcast summary created with Snipd AI

Quick takeaways

Deep dives

The Elusiveness of Green in the Sky

Scattering and Perception of Light

The Role of the Aurora and Other Green Skies

Remember Everything You Learn from Podcasts