The four elements of air colors refer to the primary colors that can be seen in rainbows, sunrises, sunsets, and other atmospheric optical phenomena. These four elements are red, yellow, green, and blue. Understanding these basic components can help explain why we see the colors we do in the sky.
Red
The color red is the longest wavelength visible color in the color spectrum. It has a wavelength range of about 620-750 nanometers. Red is one of the three primary colors, meaning it cannot be created by mixing other colors. In the atmosphere, red hues are created when sunlight passes through dust particles or pollution in the air. The particles and pollution scatter blue light away, leaving behind longer red wavelengths. Dramatic red sunrises and sunsets occur when sunlight has to pass through more atmosphere near the horizon, scattering away even more blue light. Red auroras are also caused by energetic particles from solar storms colliding with oxygen in the upper atmosphere at a specific wavelength corresponding to a red color.
Yellow
Yellow is a middle wavelength color in the visible light spectrum, with a range of about 570-590 nanometers. It is located between the red and green portions of the spectrum. Yellow is considered one of the three primary colors along with red and blue. In the atmosphere, yellow hues are created when sunlight containing the full visible spectrum passes through a translucent or thin veil of particles or clouds. The particles scatter away some blue light while allowing other colors like yellow to pass through. Yellow sunrises and sunsets occur when there is a moderate amount of particles in the air to filter out just some of the blue light. Yellow auroras can form when energetic particles collide with both oxygen and nitrogen molecules at specific wavelengths linked to the color yellow.
Green
Green has wavelengths ranging from about 490-560 nanometers, making it the middle color in the visible light spectrum. It sits between blue and yellow. Green is considered one of the three additive primary colors. In the sky, green hues form when sunlight passes through thick layers of atmosphere containing water droplets, ice crystals, or air molecules. The droplets and crystals scatter away most longer red wavelengths while allowing middle green wavelengths to transmit through. Deep green auroras occur when energetic particles interact with oxygen molecules at heights that correspond with the green color. Green is commonly seen in atmospheric optics like rainbows, halos, glories, and coronas caused by reflection and refraction of sunlight through water droplets.
Blue
Blue has the shortest wavelengths of visible light, measuring about 450-495 nanometers. It is one of the three primary colors. Blue hues dominate the daytime sky because the shorter blue wavelengths are more easily scattered by nitrogen and oxygen molecules in the upper atmosphere. This gives the atmosphere its characteristic blue color. At sunrise and sunset, the sun is lower on the horizon and its light has to pass through more air. Much of the blue light gets scattered away, allowing reds, oranges, and yellows to be seen instead. Blue auroras form when energetic particles strike nitrogen molecules at heights correlating to the blue portion of the spectrum. Blue is the most commonly observed color in rainbows, halos, and glories because of how easily water droplets scatter blue wavelengths.
How the Elements Mix
While red, yellow, green, and blue represent the primary elements, they can mix to create a wide range of secondary and tertiary colors. Here are some examples of how the four elements combine in the atmosphere:
- Orange – Made from mixing red and yellow. Seen at sunrise/sunset.
- Violet – Made from mixing red and blue. Occurs at the edges of rainbows.
- Turquoise – Made from mixing green and blue. Visible in some auroras.
- Amber – Made from mixing red and green. Found around the sun in sun dogs and sun pillars.
- Teal – Made from mixing green and blue. Seen faintly in the daytime sky.
- Magenta – Made from mixing red and blue. Occasionally noticed in vivid sunrises and sunsets.
By understanding the causes of the four primary air colors and how they blend, we gain insight into the visible beauty and science in our skies.
Scattering Effects
The primary way the four air color elements form is through scattering. Scattering refers to the redirection of electromagnetic radiation waves, like sunlight, when they interact with particles or molecules in the atmosphere. Different sizes of particles scatter different wavelengths to produce various colors.
There are two main types of scattering:
- Rayleigh scattering – Caused by particles smaller than the wavelength of light, such as air molecules. Scattering intensity increases rapidly as wavelength decreases, resulting in greater scattering of shorter blue wavelengths.
- Mie scattering – Caused by particles similar in size or larger than wavelengths of light, such as dust, smoke, water droplets, and ice crystals. Scatters all colors more evenly compared to Rayleigh scattering.
In the upper atmosphere, Rayleigh scattering by nitrogen and oxygen molecules scatters high amounts of blue light in all directions, giving the sky its blue color. In lower regions of the atmosphere, Mie scattering becomes dominant as particle sizes increase. This leads to more reds and yellows being scattered, resulting in colorful sunrises, sunsets, and optical phenomena like rainbows.
Impact of Air Clarity
The clarity of the air can significantly impact the intensity and saturation of colors we see. Clear air allows sunlight to pass through relatively uninhibited, maintaining a light blue sky color during the day. Hazy and polluted air contains more particulate matter like dust, smoke, and pollution that scatters and absorbs more light, washing out and whitening the sky. As particulate matter increases near sunrise and sunset, more blue light is scattered away, allowing richer reds, oranges, and yellows to shine through.
Here is a table comparing clear and hazy air conditions:
| Air Condition | Daytime Sky | Sunrise/Sunset |
|---|---|---|
| Clear | Bright blue | Pale yellow, pink |
| Hazy | Milky white-blue | Vivid orange, red |
This demonstrates how increasing haziness and particulate matter shifts the balance from shorter wavelengths like blue to longer wavelengths like red.
Impact of Viewing Angle
The angle at which sunlight passes through the atmosphere also significantly affects the colors we see by changing the path length light must travel. At noon when the sun is high overhead, sunlight only passes through 1-2 times the thickness of the atmosphere. But near sunrise and sunset, sunlight has to travel through 5-10 times as much atmosphere since it enters and exits at a shallow angle.
This increased path length accentuates scattering, especially of shorter blue wavelengths. With more blue light removed, vivid reds, oranges, and yellows become visible instead. Viewing angle accounts for why we don’t see these colors at noon but prominently during sunrise and sunset when sunlight is low on the horizon.
Role of the Sun’s Position
The sun’s position relative to the observer also influences the colors seen. At sunset, sunlight is scattered through the atmosphere in the direction of the observer, allowing more long red wavelengths to be seen. At sunrise, sunlight travels the opposite direction so more short blue wavelengths reach the observer instead. This gives sunrises a distinct bluish hue compared to the richer reds and oranges of sunsets.
Additionally, the time of year impacts the solar angle. During winter, the sun stays lower in the sky. Passing through more atmosphere with a high path length, it appears more red-orange. In summer, the higher solar angle produces a deeper blue sky with weaker sunrises and sunsets.
Effect of Cloud Layers
Clouds act like additional particles that can scatter and absorb light passing through them. Different cloud layers and compositions produce unique effects on the colors we see.
- Cirrus clouds high up mainly scatter blue light, leaving a paler sky color underneath.
- Altocumulus and altostratus clouds scatter light more evenly, leading to a whitish sky hue.
- Low stratus clouds mostly scatter red light, causing dull red sunrises and sunsets.
- Thick cumulus and cumulonimbus clouds block sunlight, producing gray skies.
- Wispy cirrostratus clouds can produce vivid sun pillars and sun dogs full of reds, greens, and blues.
Multi-layer clouds also filter light in complex ways. Thin high clouds combined with low clouds can generate bright crimson red sunrises and sunsets by filtering different colors twice.
Influence of Weather Patterns
Weather patterns move air masses containing different moisture, aerosols, and particle contents overhead, changing the appearance of the sky. Dry, clean air masses generally produce lighter blue skies and weaker sunrises/sunsets. But humid, unstable air before storms creates dramatic yellow, orange, and red colors as particles rapidly build.
Some examples include:
- Tropical air – Scattered puffy cumulus clouds give skies a deep blue background. Sunrises/sunsets muted gray or pink from moisture.
- Arctic air – Very clear and dry air allows dark blue sky days. Sunrises/sunsets glow orange and red as light scatters from ice crystals.
- Dry continental air – Crisp deep blue sky but hazy white near horizon from dust. Sunrises/sunsets turn vivid red-orange.
- Marine air – Milky blue sky and bright white horizons from salt haze. Red sun with green flash sunsets possible.
By understanding typical air mass properties, weather patterns can provide clues to predicting color changes throughout the day.
Role of Elevation
Height above sea level also plays a key role in the observed colors. At higher elevations, less air sits above the observer so there is less scattering of light. This results in darker blue sky days and more intensely saturated sunrises and sunsets.
Conversely, at sea level more air molecules are present to scatter light. This creates paler blue daytime skies but also vivid red sunrises and sunsets as more blue light gets filtered out near the horizon.
In the table below, typical color effects at different elevations are compared:
| Elevation | Daytime Sky | Sunrise/Sunset |
|---|---|---|
| Sea level | Pale blue | Intense red |
| 1,000 ft (300 m) | Medium blue | Vivid orange |
| 5,000 ft (1,500 m) | Deep blue | Bright yellow |
| 10,000 ft (3,000 m) | Very dark blue | Pale pink |
These patterns demonstrate how thinner air and less scattering at altitude allow colors to appear more saturated and distinct during the day but with weaker sunrises and sunsets.
Role of Latitude
Latitude also affects perceived colors by changing the angle at which sunlight passes through the atmosphere. At low latitudes nearer the equator, the sun rides higher through the sky even during sunrise and sunset. With a shallower path, less scattering occurs so skies appear azure blue and sunrises/sunsets take on a pale orange hue.
But at higher latitudes further north or south, the sun sits lower in the sky, even at noon. Sunlight takes a steeper angle through the atmosphere, enhancing scattering and coloring the sky milky white near the horizon during the day. This also causes vivid crimson sunrises and sunsets by removing more blue light.
The table below summarizes typical color effects at different latitudes:
| Latitude | Daytime Sky | Sunrise/Sunset |
|---|---|---|
| Equator | Deep azure blue | Pale orange |
| 30°N/S | Medium sky blue | Golden yellow |
| 60°N/S | Whitish horizon | Red-violet |
| Polar regions | Milky white-blue | Fiery red-orange |
These patterns show how higher latitude locations experience more color intensity due to increased scattering from the sun’s lower position.
Conclusion
In summary, the interplay of the four elements of red, yellow, green, and blue in the atmosphere creates the colorful sights we enjoy. The shades and mixtures of these primary colors are determined by factors like air clarity, viewing angle, the sun’s position, cloud layers, weather patterns, elevation, and latitude. Understanding these elements provides a window into the deeper science of light and optics occurring all around us each day.
The next time you witness a stunning sunrise, sunset, rainbow, or auroral display, think about the complex scattering effects producing the masterpiece before your eyes. Appreciating both the beauty and science of nature’s canvas in the sky allows us to be more perceptive observers of our world.