During my last trip to Tanzania, I spent several nights photographing the Milky Way under perfectly dark skies. What caught my attention almost immediately was something unexpected — on photos the sky looked unusually reddish.
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| Canon EOS Ra, Canon EF200mm f/2.8L II USM Lens, f/3.2; ISO 12800, 15 sec. one photo, Panorama 21 images, combine in Photoshop, September 22, 2025, Nyikani Migration Camp, Tanzania. |
At first, I thought it was just a trick of the weather.
But the reddish tone wasn’t just a one-night surprise — it appeared the second night, and again the third night, no matter where I set up my tripod.
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| Canon EOS Ra, Canon EF200mm f/2.8L II USM Lens, f/3.2; ISO 20000, 20 sec. one photo, Panorama 21 images, combine in Photoshop, September 23, 2025, Signature Serengeti Camp, Tanzania. |
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| Canon EOS Ra, Canon EF200mm f/2.8L II USM Lens, f/3.2; ISO 25600, 15 sec. one photo, Panorama 21 images, combine in Photoshop, September 26, 2025, Tarangire National Park, Tanzania |
Later, I went back through some of my older photos taken a few years earlier in the Galápagos Islands, and there it was again — that same faint red glow in the sky background.
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| Canon EOS 60Da, EF16-35mm f/2.8L II USM, 16.0 sec; f/2.8; ISO 6400, about 40 photos, combine in Photoshop, Feb 23, 2018, Puerto Villamil, Isabela Island, Galapagos, Ecuador. |
Four photos, two locations, years apart… and the same pattern. All were taken under dark, moonless skies far from city lights. The red glow wasn’t from pollution — it was coming from the atmosphere itself.
So I started digging to find out why.
Why It’s Redder Near the Equator
After reading through scientific papers and observing reports, I found that this red dominance near the equator isn’t a coincidence — it’s a well-known pattern.
Near the magnetic equator, the upper atmosphere gets more direct sunlight and stronger ultraviolet radiation from the Sun. That creates more ionization and more energetic electrons high above Earth. When those electrons recombine with oxygen atoms at night, they emit bright red 630 nm light.
Meanwhile, the lower green-emitting layer is denser and warmer in tropical regions. Collisions there often “quench” the green light before it can shine. So while both colors exist everywhere, the red layer wins near the equator — especially during periods of strong solar activity like the one we’re in now.
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| Toy model: Airglow “color” vs latitude (Green 557.7 nm / Red 630.0 nm) |
A Simple Way to Imagine It
Think of it like two glowing shells around Earth:
- A lower green shell — thicker air, more collisions, so light is often quenched
- A higher red shell — thinner air, stronger ionization, shining freely into space.
At higher latitudes, the green layer shines more clearly. Near the equator, the red shell becomes brighter and overshadows it. My camera was basically looking through more of that red upper layer, capturing a stronger crimson glow.
The Beauty of Accidental Science
I didn’t set out to study airglow — I was just chasing the Milky Way. But sometimes astrophotography turns into a kind of quiet citizen science. My four “anecdotal” photos ended up showing a real global trend that scientists have been measuring for decades.
It’s a reminder that even casual night photographers can notice patterns that connect directly to planetary physics. Next time you shoot the night sky near the tropics, look closely when you process your images. If you see a faint red haze in the background, that’s not light pollution or a white-balance mistake — it’s Earth’s upper atmosphere glowing.
Final Thoughts
Standing under the African night with the Milky Way overhead and the warm breeze on my face, I realized that the sky’s color is not fixed. Even in darkness, our planet shines with its own quiet heartbeat — a breath of red light from hundreds of kilometers above.
The next time you photograph a dark sky, remember: sometimes your camera captures more than stars — it records the living atmosphere of the Earth itself.
