Why is the Sky Red? A Deep Dive into Sky Color Science

Vivid red skies have inspired philosophers, photographers, and scientists alike to ponder what makes the heavens blaze crimson. As a tech geek and weather enthusiast, I‘m fascinated by the optics and atmospheric physics behind sky colors. Let‘s geek out on the science of red skies and other sky color wonders!

Overview: Rayleigh Scattering Explained

For typical blue skies, sunlight penetrates the atmosphere and shorter wavelengths like blue and violet are scattered by tiny air molecules. This is called Rayleigh scattering, named after physicist Lord Rayleigh. But when the sun nears the horizon at sunrise or sunset, its light passes through more atmosphere and more blue light is filtered away. This allows the longer red and orange wavelengths to shine through, creating a vivid red sky.

Here‘s a snapshot of key Rayleigh scattering facts:

• Responsible for blue skies and red sunrises/sunsets
• Selectively scatters shorter wavelength colors
• Caused by tiny particles like air molecules or particulates much smaller than light wavelengths
• More pronounced at low sun angles since light passes through more atmosphere

But Rayleigh scattering doesn‘t fully explain the most intense red skies. For that, we need to look at Mie scattering.

Intensifying Factors: How Particle Scattering Boosts Red

Under normal conditions, air molecules alone create a modest red sunset. But with more particulates in the air, sunlight interacts with larger particles through Mie scattering theory, named after German physicist Gustav Mie. This enhances the vivid reds and oranges.

Some key factors that intensify red skies:

• Pollution – Smog, smoke, and haze contain more scattering particles that boost red wavelengths.
• Humidity – Water vapor molecules enhance scattering compared to dry air.
• Cloud Coverage – Low clouds reflect and diffusely illuminate reds and oranges.
• Volcanic Eruptions – Massive particulates in the stratosphere create blood red skies lasting years. The Krakatoa eruption produced notable red sunsets as far away as Europe.
• Time of Year – Longer summer days allow sunsets at a lower angle with more dramatic scattering.
• Dust Storms – Large dust particles amplify red/orange light scattering, producing eerie yellow and red skies.

In extreme cases, particle scattering can even eliminate blues entirely, leaving only deep reds and oranges in the sky.

Digging into the Optics: Light Wavelengths and Scattering

Let‘s geek out on the optical physics behind it all and look at how light wavelength relates to sky color:

Color	Wavelength Range	Scattering Effect
Violet	380-450 nm	Most scattered
Blue	450-495 nm	Very scattered
Green	495-570 nm	Medium scattering
Yellow	570-590 nm	Low scattering
Orange	590-620 nm	Minimal scattering
Red	620-750 nm	Least scattered

Shorter wavelength violet and blue are preferentially scattered, giving the sky its blue hue. The long red wavelengths pass straight through with little scattering, only becoming visible when the sun peers through extra atmosphere near the horizon.

Now let‘s compare Rayleigh and Mie scattering in more detail:

Factor	Rayleigh Scattering	Mie Scattering
Cause	Scattering off air molecules	Scattering off larger particles
Particle Size	Much smaller than light wavelengths	Similar or larger size than wavelengths
Effects	Blue sky, red sunrises/sunsets	Enhanced vibrancy of sunrises, polluted skies
Examples	Clean, dry air	Haze, humidity, volcanic ash

Rayleigh handles the baseline red skies from air molecules, while Mie intensifies the reds through added particulates. Together, they orchestrate nature‘s colorful masterpiece!

Rare Sky Events and Optical Phenomena

Beyond typical sunrises and sunsets, some rare and stunning sky events can occur under just the right conditions:

Green Flash

Right before the sun vanishes below the horizon, a bright green spot sometimes flashes for a few seconds. Caused by atmospheric refraction separating light into its spectral components, it takes extremely steady air and an unobstructed view to witness this elusive phenomenon. I was lucky to catch a green flash while photographing a sunset in Hawaii!

Rainbow Tornado

When a rain-wrapped tornado forms on the sunrise side of a storm, direct sunlight can refract through the raindrops to create a vivid rainbow tornado. The last documented case was a rainbow wrapped around an Oklahoma tornado in 2004, captured in a well-known photo by Eric Nguyen.

Noctilucent Clouds

These electric blue wispy tendrils illuminate the night sky well after sunset, forming in the upper mesosphere around 50 miles high. Also known as polar mesospheric clouds, they are made of ice crystals from meteor dust. I recently saw these otherworldly clouds after sunset above the Oregon coast.

Mammatus Clouds

Dramatic pouches hanging under the anvil of a thunderstorm indicate strong turbulence and updrafts. Mammatus clouds are an ominous sign of an intense storm. The unique structure still confounds scientists but makes for incredible photos, like this mammatus spectacle my wife and I drove through in South Dakota.

Capturing images of fleeting sights like these requires perfect timing, an unobstructed view, and often long-distance travel to witness. But the reward is an unforgettable sky spectacle that few get to experience.

Photographing Red Skies

Now let‘s shift gears to photographing red skies. While smartphone cameras do a decent job, DSLR and mirrorless cameras provide more controls for pro-level sunsets. Here are my top tips:

Use Low ISO – Higher ISO leads to noisy images, so use the lowest native ISO your camera offers (typically ISO 100 or 200). This ensures maximum detail and color depth.

Reduce Aperture – Choose a higher f-stop aperture, such as f/11 or higher, for maximum image sharpness from foreground to sky.

Select White Balance – For vivid sunsets, use the Daylight or Cloudy white balance setting. You can customize white balance for ultra accurate colors.

Shoot RAW – RAW retains more color data and dynamic range vs JPGs. This allows correcting white balance and exposure to bring out the vivid red tones.

Include Foreground – Compose using a subject in the foreground like a tree, person, or building to add depth and scale.

Bracket Exposures – Take several shots at different exposures to ensure you capture detail in the sky as well as the landscape.

Time it Right – The most intense colors often occur in the minutes right before the sun disappears below the horizon.

Use Filters – Consider a neutral density filter to allow longer exposures and cloud motion blur during twilight. A circular polarizer will intensify colors and reduce glare.

With the right gear, settings, and technique, you can create spectacular photos of the world‘s most vibrant sunrises and sunsets.

Predicting Red Skies and Storms

Red evening light is a joy to photograph, but a red sunrise can signal an approaching storm. Here are some tips for forecasting intense sunrises and storms:

Monitor Weather Reports – Stay up to date on forecast models, warnings, and satellite/radar maps to understand severe weather risks in your area.

Inspect Cloud Types – Cumulonimbus clouds are signs of powerful thunderstorms. Altostratus or cirrostratus clouds indicate a weather front is approaching.

Detect High Humidity – The higher the humidity, the more vibrant the reds and chance of storms ahead. Humidity also brings out rainbows.

Watch Wind Direction – Surface winds blowing from the south often draw up moisture, signaling potential storms coming your way.

Note Temperature Changes – Rapid warming in winter followed by drops into the 50s F point to dynamic weather on the way as cold fronts push through.

Observe Animal Behavior – Animals often become anxious before major environmental disturbances like storms. Odd bird migrations or herd movements can be clues.

By reading environmental cues and combining scientific weather intelligence, you can prepare properly for intense weather photographers dream of capturing.

The Beauty and Mythology of Red Skies

Red skies have inspired people worldwide for millennia. Ancient myths link red skies to cosmic battles and fire in many cultures. Here are some iconic examples:

Ancient Egyptians – Believed red mornings symbolized the god Ra‘s rage. Ra was portrayed with a red disk for a head.

Greeks & Romans – Saw red skies as omens of stormy weather brought by the god of rain, Zeus/Jupiter.

China – Associated red skies with war and turmoil in dynastic times. Red represented fire, an essence of the Chinese god of war Guan Yu.

Hindu Texts – Linked red dawns to doomsday prophecies of pralaya, or the destruction of the universe in cosmic fire.

The Bible – Contains verses interpreting red evenings and mornings as signs of fair and foul weather ahead.

Norse Mythology – Saw vivid sunsets as a sign Ragnarok "Doomsday Winter" was coming, preceding epic battles among gods and apocalyptic natural disasters.

Native Americans – Believed blood-red skies signified good buffalo hunting ahead and fortune for their tribes.

Red sky myths helped cultures interpret nature before meteorology emerged. While we now understand the optics behind red skies, their splendor still evokes a sense of awe today.

Final Thoughts: The Science of Sky Color

Hopefully this deep dive shed light on what makes skies turn red and even rarer colors. Rayleigh and Mie scattering, together with a dash of weather conditions like humidity and pollution, orchestrate nature‘s vivid sky palette. As cameras and science progress, we keep learning more about atmospheric phenomena and physics. Emerging technologies like computer vision algorithms and AI could someday help us forecast rare events like green flashes hours in advance. I look forward to the day photographers can plan trips specifically to witness elusive sights based on super-accurate sky color predictions. For now, keep looking up and appreciating the science and beauty behind each color-filled sunset and sunrise!