Although the sky is blue most of the time, it isn’t always the color of the heavens above, especially in the morning and beginning of the night, making us ask, “Why is the sky red?”
In this article, we will discuss why the sky turns red during sunsets and sunrises.
It is a myth that these events get their color from pollution. However, pollution can contribute to its vibrancy, especially when it comes to red.
We’re going to break down the reasons we can see a red sky and if they can also cause a red moon. Ready? Let’s go!
Why Is The Sky Red?
Throughout the ages, red skies have been blamed on many things:
- Angry gods
- An impending apocalypse
- Red sky in morning, sailor’s warning
- Red sky at night, sailor’s delight
The truth is that the sky isn’t red at all. But that’s how we perceive light, which is scattered through the atmosphere when our primary source of white light, the sun, is the farthest away from us. It all boils down to wavelengths and scattering light.
How Does Light Scattering Make The Sky Red?
Light scattering makes the sky appear red at certain times of day or situations, such as a forest fire or volcanic eruption. It all depends on how light travels and can be “scattered.”
Light travels at the speed of…well, light. (The only being or object capable of traveling faster than light is the 1978 Superman, who can fly so fast he turns back time to save Lois.)
The complete electromagnetic spectrum encompasses all types of light, including radio waves, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays.
And you probably know what color is, right? Hint: Color is visible light—the tiny part of the spectrum our eyes can see.
(Curiously, some animals can see ultraviolet light, meaning they can probably see a beautiful, more colorful sunset.)
Anyway, each color travels on its own wavelength. Some are high energy and short, such as violet light at 380 nanometers (nm). Some are low energy and long, such as red light at 700 nm.
But light is scattered all the time. Most of the time, the scattering of light makes the sky appear blue. However, this can change when the sun is lower in the sky, enabling different colors to be viewed, such as red.
Good to know: Unlike the sky, which scatters light, the ocean is blue because it absorbs light (and then it scatters the blue).
Rayleigh Scattering: Why Can It Make The Sky Red?
The answer to “Why is the sky red?” lies in the Rayleigh scattering.
It is a process of light dispersion, named after the man who discovered the phenomena, John William Strutt, otherwise known as Lord Rayleigh. (Yes, British names and titles can be very confusing.)
When light passes through our planet’s atmosphere, it has to pass through gasses and dust particles. Long wavelengths, such as red, easily pass through these gasses. However, the shorter wavelengths, like blue and violet, are disrupted, hence the term “scattering.”
So, just as light waves traveling through rain will paint a rainbow across the sky, blue light passing through the atmosphere coats the sky blue (our eyes don’t detect violet wavelengths as easily).
However, things get more complicated when the sun is low, as it is for sunrises and sunsets. Light waves now have to travel further to reach our eyes.
Since blue light is one of the shortest wavelengths, it is increasingly scattered the further it travels, so we can hardly see it during these times of the day. Instead, we see the longer wavelengths: red, orange, and yellow light. Thus, we can get a red sky.
Tyndall Effect: Why Can It Make The Sky Red?
The Rayleigh scattering isn’t the only answer to “Why is the sky red?” There is also the Tyndall effect (also known as the Tyndall phenomenon).
It is when light is scattered due to particles larger than what exists naturally in our atmosphere. An example is the floating moats you see in a beam of light coming through a window or flashlight.
The Tyndall effect is why places of high air pollution have such a vibrant sky at sunset. It is also why large amounts of smoke can cause a red sky.
But the Tyndall effect and Rayleigh scattering work in the same manner. The only real difference is the size of the particles.
Red Moon: Rayleigh Scattering, Tyndall Effect, Or Eclipse?
The sky is not the only thing that can have different colors. Have you ever wondered how blood moons occur?
Blood moons have many legends, but they result from a lunar eclipse.
During the eclipse, light passes through our planet’s atmosphere first before hitting the moon. So essentially, the Rayleigh scattering is causing the moon to appear red. Cool, right?
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