As we begin The Two Towers, we find our heroes Aragorn, Gimli, and Legolas chasing a band of Uruk-hai, elite orcs serving the Dark Lord Sauron and the corrupt Saruman. The trio of heroes were attempting to rescue their hobbit friends Merry and Pippin, taken hostage by the Uruk-Hai. As Aragorn, Gimli, and Legolas follow the trail, dawn breaks, and Legolas exclaims, “A red sun rises. Blood has been spilled this night.”

When I first heard this, I thought it was just some cheesy phrase, something added to the film to sound all cool and mysterious.

I was wrong. There actually is a reasonable science-based explanation on why a red sun could be linked to death.

In the follow-up to this quote, the Riders of Rohan, skilled soldiers mounted on horses, come upon the trio. Éomer, leader of the Riders, states that the riders killed the Uruk-hai, piled the bodies, and burned them.

It was the burning of the bodies that caused the red sun.

Particles in the atmosphere affect how we see the sky. Light from the sun is scattered by molecules in the air- that is, when the light hits an air molecule, the light pathway changes direction. These air molecules tend to scatter light with shorter wavelengths (such as blue) more often than light with longer wavelengths (such as red). This is part of the reason why we see blue skies– the blue light traveling throughout the atmosphere is scattered in all directions, while the rest of the light is more likely to pass through. As a result, we see the scattered blue light filling up the sky.

Meanwhile, if you were to look directly at the sun overhead on a clear day (note: not recommend), the sun would probably look slightly yellow to you. The shorter blue light is scattered out of the sunlight’s path to your eye, allowing the longer red-orange-yellow light to pass through to reach you. When the sun is close to the horizon, it generally takes on a more orange or red tinge. That’s because the sunlight is passing through more of the atmosphere to reach your eyes. By passing through a thicker layer of air, even more blue light is scattered, pushing the visual image of the sun to the red side.

Additional particles from smoke or dust scatter even more blue light away, making the sunlight source to appear even redder. Thus, a redder-than-normal sun could indicate something burning in the area, as the smoke particles scatter out the blue light.

This phenomenon was seen in the recent outbreak of wildfires in California. Many people noted that the smoky haze from the fires were causing the sun to appear red. (Some even quoted The Two Towers.) The wildfires were pushing smoke particles out into the air, filtering out the blue light and turning the sun red.

Going back to The Two Towers, the rising sun probably looked red because of the smoke rising from the pile of burning bodies. Turns out a red sun really does mean that blood was spilled in Middle Earth.

Keep calm and science on.

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