Not too long ago, I settled down in my bedroom to dip into a good book. Nothing seemed out of the ordinary — just a typical evening.
But after an hour or so, I noticed the pages of my book had taken on an antique-yellow hue though I had bought it new that week.
I puzzled for a moment, looked up, and to my surprise, the entire room was drenched in a golden ambient light. I moved to the window, peered out, and marveled at the glorious yellow suffusion in the sky.
It was as if some greater being had drizzled syrup all over us like a big old stack of pancakes!
What the heck was going on, I thought to myself, never having seen such a skyscape in all my days. So I did some research and found that this xanthous wash wasn’t a one-time thing, but an optical phenomenon, experienced time and time again.
Here’s why it happens!
The Quick Answer
As is the case with almost all sky-based optical phenomena, the striking yellow sky was created by the interplay of sunlight and our atmosphere.
The gasses and particles that make up the layers of Earth’s atmosphere don’t let light through without a fight, and when it finally makes it to us, in a sense, it’s bruised and bloody, a colorful distortion of its former self.
When I witnessed the caramel sky, it was evening time, but it also quite commonly occurs in the early morning as well. This is because the sun’s light has even further to travel at the poles of the day.
Clouds can also bully light on its way through, often to spectacular photic results. In fact, they have the most impact of any other attached party, but let’s take a closer look at all contributing factors, shall we?
Sun Rise, Sun Set: The Solar Journey
As you know, a day is a measurement of one 360-degree planetary rotation.
On Earth, it so happens that a full 360° rotation takes approximately 23 hours and 56 minutes, and during this time, the sun will rise and then it will set, with the only exceptions being the North and South Pole, and Svalbard in Norway.
At the poles of the planet, the sun will neither rise nor set for periods of time that seem completely alien to us.
Svalbard, being so northern in the hemisphere, also experiences what has been labeled the midnight sun, when the sun still hangs in the sky past 12 pm. But what’s going on here?
The Earth rotates east to west, and as it goes, a different portion of the planet’s surface is exposed to the sun’s light, accounting for the sun’s rising in the west and setting in the east.
When night tide washes over your home, the far westward lands are just waking up.
Although it appears as if the sun is rising and setting, it’s not moving at all, and the light is only ever traveling in one direction.
The motion is actually all taking place on Earth, but as we don’t physically feel the Earth’s rotation, the sun seems like the dynamic party.
Seasonal Variability: The Earth’s Orbit Around The Sun
Of course, the Earth isn’t only rotating on its axis, it’s also rotating around the sun, which has no effect on the length of the days for those hugging the equator, but for those in closer proximity with the poles, a shifting of sunrise and sunset times will occur.
The closer to the poles you are, the more seasonal variability you’ll experience. In other words, if you’re far away from the equator, you’ll experience shorter days in winter, and longer days in summer, and it’s all because the planet is on the wonk.
Yep, that’s right, folks, the Earth sits on its axis at a jaunty 23.5°, which alters how the light of the sun can interact with us here on the planet’s surface.
This angular orbit is why somewhere like Norway will have totally different daylight durations than somewhere like Rome at the exact same point in the year.
We may not strictly be able to see the earth’s atmosphere, but that’s not to say that it isn’t of crucial importance.
Without it, there would be nothing to dilute the power of the sun’s rays, and the Earth would literally cook, leading to the evaporation of all liquid water, the banishment of oxygen, and, needless to say… the demise of all living things.
Composed of five distinct layers, this atmospheric armor does its job marvelously, but the one we should concern ourselves with in this context is the very first of them, the troposphere. (also see ‘What Is The Mesosphere, And What Are The Characteristics That Define It?‘)
The troposphere extends 4–9 miles from the Earth’s surface, and it contains the lion’s share of the Earth’s nitrogen and oxygen.
Also referred to as the weather sphere, the troposphere plays host to all earthly weather events. It’s where the clouds form, and thus where the rain falls from and the lightning lives!
And with plenty of airborne elements to throw into the way of light on its way to Earth, it’s this first atmospheric layer that’s most responsible for the various colors we see in the sky (also see ‘Why The Sky Is Blue… A Closer Look‘), including the yellow I experienced while reading my book.
Light: The Coloring Pencils Of The Clouds
Although that fuzz of morning light creeping in through the cracks between the curtains appears to have a subtle but distinct hue, light itself is actually completely colorless.
For instance, during its journey through the void that separates the sun and Earth, it doesn’t look like anything, a photic phantom flying through space.
Untarnished visible light from the sun would be pure white, or translucent anyway, but the white of light isn’t technically a color of its own, rather the sum of multiple wavelengths representing different colors.
The gas molecules of the troposphere effectively bully this pure white light on its way through. They reflect some, they deflect some, and they hold on to some through absorption too.
These molecules are hungry for light, and the frequency in sunlight with the most energy is blue, so that’s their favorite target. They scatter the blue wavelengths all over the place, and as a result, when we look up, the sky appears to be blue.
See how impactful the troposphere is to our perception of color? It’s nuts, right? And we haven’t even talked about clouds yet.
Clouds are composed of water droplets, fine ice crystals, or a bit of both, which gives them plenty of ammunition for their clash with light.
Exactly what the result of said clash winds up being, however, comes down to the nature of the cloud in question. Some will be more reflective, while other diaphanous forms will let more light trickle through.
Some will alter color significantly, while others will not.
Let’s take a look at how the different cloud forms interact with the radiation of sunshine.
There are ten major cloud forms, but for the sake of brevity, we need only concern ourselves with three:
Cirri are typically one of the highest cloud forms of all. While they have a number of species and a couple of variations, they’re often quite thin and wispy, allowing light to pass through… but not unscathed.
Cirrus clouds are composed primarily of fine ice crystals, each of which acts like a tiny prism, which sometimes creates cloud iridescence — Sort of like an oil puddle in the sky.
Cumulus clouds are multi-height clouds that typically inhabit the upper end of the lower troposphere and the lower end of the middle troposphere.
These are the quintessential cloud formation, the kind that you picture when you think of a cloud; the kind of cloud a child might draw.
Much like the cirrus, this cottony cloud form has multiple species, the most notable of which is the cumulonimbus, or in plain English, thunderstorm clouds.
And this brings us to our lowest cloud form, the stratus. These clouds lack any definite structure and often contribute considerably to overcast. Stratus clouds are some of the most adamantine to light, especially the nimbostratus species.
As mentioned above, these cloud types inhabit different portions of the troposphere, which is split into three categories (low, middle, and high). Two of these categories have their own prefix for further cataloging cloud species.
- High – Cirro
- Middle – Alto
- Low – No prefix
The three most common high clouds are the standard cirrus, the cirrostratus, and the cirrocumulus. The prefix informs of altitude, while the latter section of the name indicates the cloud family. These clouds can be found beyond 20,000 feet.
The two primary middle clouds are the altocumulus and altostratus, both of which hang around the 6500 feet mark.
Low clouds are far less varied, which is why they don’t get a prefix. You’ll most likely only see your garden variety cumulus, and just below, your bog-standard stratus.
Sometimes, however, there will be vertical clouds present, formations that cross altitude boundaries.
So Why Does The Sky Turn Yellow?
As we’ve already established, the blue wavelengths of visible light are scattered as a result of the light’s interaction with our atmosphere.
At dawn and dusk, the sun’s light has further to travel, which means more of its wavelengths get scattered, especially when trying to nose through certain cloud forms.
Sometimes, only the longest wavelengths of visible light get through, the hotter colors (yellow, orange and red), which is why the sky sometimes appears yellow.
All sunsets follow the same principle, but they will often become visibly pink or red due to the interference, not just of gas molecules and clouds, but dust particles too, which are capable of distorting the red wavelength of sunlight.
Clouds And Reflection
The wooly clouds that linger at the low and alto portions of the troposphere don’t let a lot of light through, so if there’s a surplus of stratus or cumulus fuzz in the sky, we won’t see any interesting colors at sunrise or sunset.
We’ll simply watch the world get dimmer, gradually fading into night.
The higher clouds that inhabit the cirro section of the troposphere are more forgiving in terms of light passage, but not so when it comes to distortion, which is what gives us our technicolor sky.
Colors can be even more vivid as the sun arrives or drips away, as the light is distorted on the underside, rather than the top of the high clouds, giving us that sediment-like spread of color reaching way beyond the horizon.
In certain rare circumstances, the clouds can interact with the sunlight in such a way that the resulting color spreads much farther across the sky, which is what I experienced in my room that day — a golden expanse, as if Midas had reached up and tickled the heavens.
That yellow light bath we sometimes experience is the product of some pretty complex physics, but once it’s all broken down like this, it’s pretty easy to glean.
To summarize, colorful skies, yellow or otherwise, are caused by white light’s conflict with gas molecules, dust, and clouds in our atmosphere, with the troposphere having the most significant effect.
Together, these opposing parties paint the sky like a canvas, leaving us here on Earth dumbstruck by the beauty and splendor of our world.