The colors we see in the sky at sunrise and sunset are some of the most beautiful and captivating sights in nature. But what causes those stunning red, orange, yellow, pink and purple hues? The colors are determined primarily by the scattering of sunlight off molecules and particles in Earth’s atmosphere. Here we’ll explore the science behind sunrise and sunset colors.
What Makes the Sky Blue During the Day?
During the day, the sky appears blue because sunlight is scattered by gas molecules in the atmosphere. Shorter wavelength blue light is scattered more than longer wavelengths, causing the sky to take on a blue hue.
When the sun is overhead, sunlight passes through less atmosphere and experiences less scattering. But when the sun is lower in the sky at sunrise or sunset, sunlight passes through more atmosphere and more scattering occurs. This removes the blue wavelengths, allowing the reds and yellows to shine through.
What Causes the Red and Orange Colors?
As the sun starts to set, sunlight has to pass through more atmosphere to reach our eyes. More of the blue light is scattered away, leaving the longer wavelengths of red and orange to travel through.
In addition, the low angle of sunlight during twilight hours means the light must travel farther through the atmosphere. This increases the scattering of blue light and allows more reds and oranges through.
The amount of dust and pollution in the air can also intensify the reds and oranges. More particles in the air leads to increased scattering of shorter wavelengths.
Where Do the Other Hues Come From?
The interplay of sunlight and cloud conditions can create beautiful bands of color at sunrise or sunset. Here are some of the colors and their causes:
|Yellow||Medium wavelength light, more dominant as sun rises/sets|
|Pink||Combination of red and blue/purple light|
|Purple||Scattering of shortest blue wavelengths off particles|
|Green||Mix of yellow and blue light from sun and sky|
The distribution of colors varies by location too. Places with more moisture and dust like tropical areas tend to have fiery red sunrises and sunsets. Dry locales like deserts or higher elevations may show more purple and orange hues.
How Do the Colors Change Throughout Twilight?
The dance of colors evolves dramatically in the 30-60 minutes before sunrise or after sunset. Here’s what you typically see:
- Predawn: Deep blues, purples, some red if clouds are present
- Sun approaches horizon: Yellows start to emerge, pink bands may appear
- Sun breaches horizon: Burst of yellow with orange and red; blue fades away
- Sun lifts higher: Blues regain dominance as other colors fade
- Sun high: Normal daylight with blue sky
- Sun starts descent: Some yellows and oranges establish
- Sun nears horizon: Intense yellows, oranges and reds dominate
- Sun drops below horizon: Reds fade to purple then dark blue
These changes happen fast, so it’s worth watching the full sunrise or sunset if you can!
What Factors Affect Sunset and Sunrise Colors?
Many variables influence the colors we see at dawn and dusk. Some key factors:
|Factor||Effect on Colors|
|Cloud cover||More clouds reflect and scatter light in interesting ways|
|Pollution, dust||Enhances reds and oranges|
|Moisture, humidity||Deepens reds and purples|
|Elevation||Clearer air at high elevations increases scattering|
|Time of year||Shorter twilight in summer limits colorful phase|
The nocturnal boundary layer also has an effect. This is the layer of atmosphere directly above the earth’s surface at night. The temperature, humidity and wind in this layer impacts the appearance of sunrise and sunset.
Tips for Viewing Sunset and Sunrise Colors
Here are some tips if you want to photograph or just enjoy the splendid sunrise and sunset colors:
- Be set up at least 30 minutes before sunrise/sunset for the full color spectrum
- Orient yourself with an unobstructed view towards the east (sunrise) or west (sunset)
- Higher elevations let you see more of the sun’s path, enhancing colors
- Avoid looking directly at the sun by focusing on the whole skyscape
- Use a foreground element like a landmark or person to add visual interest
- Wait for the colorful afterglow just after the sun dips below the horizon
The interplay of science, nature and weather makes every sunrise and sunset a unique experience. Appreciating both the beauty and science behind the colors can make these daily events even more breathtaking.
The vivid colors painting the sky at sunrise and sunset have scientific origins. Shorter wavelengths like blue and purple scatter away, while longer reds, oranges and yellows come through. Air molecules, pollution, clouds, weather and location all influence the fantastic hues. The colors change quickly, so be ready to enjoy the full spectrum in all its glory! Understanding a little science behind the sunrise and sunset can further deepen our appreciation of their ephemeral beauty.