Episode 2 - Why is the sky blue?

It's that strange time of day, right before sunset. Golden hour. You find yourself in a meadow. Surrounded by wildflowers. The sun bathes everything in a golden glow. Creating long shadows, and stark contrasts across your field of view. The sky remains blue. They say that sunlight is actually white. But as it passes through our atmosphere the blue get's filtered out, and causes the sky to light up. The diffusion of blue is so great that it obscures our view of the stars during the day. But if you wait a few moments, it'll be dusk, and something remarkable will happen. 

 

The light blue of the sky directly overhead, starts to deepen, and the flowers around you start to fluoresce. Their green stalks turning almost black, but their petals becoming brighter than their surroundings should allow. Could it be the sky is now deepening into the ultra violet range? That even though the daylight is dwindling as the sun scorches the other side of the planet, somehow the blue is retreating with it, leaving only a pale haze of ionizing radiation, dotting the ground with faint tracking lights, allowing the birds to find their roosts.

 

At the horizon, the sun is now bright red. The sky starts to transition from red to indigo as you let your gaze wander up from our nearest star. If you take a perfect sunset, across the entire dome of the sky and compress it into a single, thick line, you notice that it makes a full spectrum, like a rainbow. Red at the horizon, orange, yellow, green, cyan, blue, indigo, violet at the opposite horizon. 

 

The sunlight is now refracting across the entire troposphere. The sparse stratosphere, containing mostly Nitrogen and Oxygen, who's molecules are just large enough to refract blue light, is no longer the dominant refractive force in our atmosphere, and the sun, now shining through the troposphere is subject to larger molecules, aerosols and dust. We live in a vast prism. A single water droplet caught in an incredible cosmic fog of gravity wells. 

 

Why is the sky blue? The question is common, but lacks an understanding of the nuance of colour, of light, of time... The sky is all colours, it just depends when you choose to look up. And where... and for how long.

 

Light is tricky. It's a particle, it's a wave. It can pass through objects, reflect off of them, bend, stretch, and become absorbed. You see, it all comes down to electrons. Close your eyes and imagine a ball, surrounded by television snow. This is an atom. The snow is the atom's electron cloud. The electrons can be found in discrete layers surrounding the atom, like an onion. For this exploration let's imagine the electrons are on springs. They are movable and tend to have specific natural frequencies that are determined by how far away from the nucleus they are. Similar to a tuning fork. If a light wave of a particular frequency strikes a material containing electrons with that same natural frequency, it gives the atom a shove. Turning the light energy into vibrational energy, as the atom resonates like a struck bell it passes that vibrational energy on to neighbouring atoms, turning vibrational energy into thermal energy within the material. In this case the photon is absorbed. Never to be released again in the form of light. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies of visible light. You can see these absorption lines if you hold a lens up to the spectrum generated by a prism. We can use this knowledge to probe chemical makeup of everything from crime scene evidence to the composition of stars across the observable universe.

 

Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural frequencies of vibration of the objects. When light waves of these frequencies strike an object, the electrons in the atoms of the object begin vibrating. But instead of vibrating in resonance at a large amplitude, the electrons vibrate for brief periods of time with small amplitudes of vibration; then the energy is reemitted as a light wave. If the object is transparent, then the vibrations of the electrons are passed on to neighboring atoms through the bulk of the material and reemitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. If the object is opaque, then the vibrations of the electrons are not passed from atom to atom through the bulk of the material. Rather the electrons of atoms on the material's surface vibrate for short periods of time and then reemit the energy as a reflected light wave. Such frequencies of light are said to be reflected.

 

Refraction is stranger still. It's a cousin to transmission, in that it allows light through via transmission, but different wavelengths travel at different speeds through the material. Longer wavelengths tend to propagate with little deviation, while shorter wavelengths curve more aggressively due to their higher rate of interaction. So Red light goes almost straight through, while the path of blue light is distorted. In the case of our atmosphere, Oxygen is just the right size for blue light to give our O2 molecules a little shove and be re-emitted at a random angle from the angle of incidence. This means that, during the day, our sky is a hazy blue, as the light from the sun has been commandeered by our Oxygen and sent careening across the sun lit sky. A similar phenomena can be found in the blue of people's eyes. There is actually no blue pigment. Instead, the light goes in, blue light bounces around and is reflected back out, creating a blue hue.  

 

The same processes that govern our perception of colour, govern our visual perception of beauty and form. Eyes blinking slowly, looking up under heavy lids, lips parted slightly, slow breath, warm and familiar. An inhale is a journey of oxygen from your lungs to theirs. Close and safe. One can scarcely say there's a defining line between you. Air, light, warmth, space are all shared. You are a part of it all, and all of it is within you. One last breath and you dissolve into the room. A super-critical fluid, with no definition, and no boundaries.