Last night, many people noticed the sky looked unusually bright orange. This strange sky color was likely caused by a few possible factors that led to increased scattering of certain wavelengths of light at sunset. In this article, we’ll explore the most common reasons for an intense orange sky at night.
Common Causes of Orange Night Skies
There are a few typical explanations for why the sky can appear a vivid orange hue in the evening:
| Forest fire smoke and haze |
| Dust storms |
| Air pollution |
| The angle of sunlight at sunset |
Let’s look at each of these factors in more detail.
Forest Fire Smoke and Haze
One of the most common reasons for an intense orange sky at night is smoke and haze from forest fires. Wildfires that are burning nearby or even hundreds of miles away can cause particles and aerosols to become suspended in the atmosphere.
As the sun gets lower in the sky, its light passes through more of this haze and smoke. The particles in the air scatter blue light, allowing more red and orange wavelengths to pass through. This gives the illusion of a rich orange or even red hue to the sky.
For example, major wildfires in California often cause orange skies as far away as Idaho, Utah, and Colorado due to the massive amounts of smoke blowing eastward. The worse the fires and thicker the smoke, the more vibrant the sunset colors become.
Dust Storms
Similar to smoke, large dust storms can also create vivid orange nighttime skies. Dust particles and other desert aerosols have a similar scattering effect on sunlight to cause warm sunset tones.
Major dust storms originating in arid regions like the Sahara Desert occasionally sweep across the Americas all the way to the Eastern Seaboard. Sunsets and sunrises during these events take on a pronounced orange glow.
The dust clouds essentially create the lighting conditions of a permanent sunset/sunrise all day long when they pass overhead. This leads to very dramatic orange hue in the sky both morning and evening.
Air Pollution
Air pollution from human sources like automobile emissions, industry, and power generation also increases the amount of particles in the air similar to dust storms and wildfire smoke.
High levels of air pollution containing lots of nitric oxide, ozone, volatile organic compounds, and nitrogen dioxide can lead to vivid orange and red sunrises and sunsets. These air pollutants all contribute to scattering blue light and allowing more orange and red wavelengths to pass through a polluted atmosphere.
Major cities like Los Angeles, Beijing, and New Delhi are known for their smoggy, hazy sunsets tinted orange due to dense air pollution. The worse the air quality, the more pronounced the orange glow during twilight hours.
Sunset Angle
The lower the angle of the sun in the sky, the further its light has to pass through the atmosphere. This allows more scattering, diffusion, and filtration of sunlight, removing shorter blue wavelengths while allowing longer yellow, orange, and red wavelengths to reach your eyes.
During winter months, when the sun follows a lower arc across the sky, vivid orange sunsets and sunrises become much more common. The sunlight takes on an orange hue more readily thanks to the steeper atmosphere it has to traverse at sunset and sunrise.
So even on a clear day with no haze, smoke, dust or pollution, a low winter sun can easily produce brilliant orange tones near the horizon. The effect is enhanced when any of the scattering particulates mentioned above are present in the air.
Conclusion
In summary, the main factors that can create a vivid orange night sky are:
| – Forest fire smoke and haze |
| – Dust storms |
| – Air pollution |
| – Low sun angle at sunset |
When smoke, dust, and pollution are high, and the sun is low in the sky, you get maximum scattering of blue light. This allows fiery orange and red wavelengths to flood the sky at sunset and sunrise.
So next time you notice an intense orange glow at night, it may be due to any of these common atmospheric conditions. The more particulate matter in the air, the more dramatic the orange color will appear as the sun dips below the horizon.
It’s simply physics and optics at play! The particles in the air preferentially scatter blue light, and let the long wavelength orange and red colors shine through. This simple scattering process gives us brilliantly colorful sunrises and sunsets to enjoy.
References
[1] Seinfeld, J. H., & Pandis, S. N. (2012). Atmospheric chemistry and physics: from air pollution to climate change. John Wiley & Sons.
[2] EPA (2018). Causes of Atmospheric Scattering. Retrieved from https://www.epa.gov/atmospheric-scattering
[3] Lee, R. (2019). Why Dust Storms Make Brilliant Sunsets. EarthSky. Retrieved from https://earthsky.org/earth/why-dust-storms-make-brilliant-sunsets
[4] NASA (2011). Vivid Sunsets Intensify with Pollution. Earth Observatory. Retrieved from https://earthobservatory.nasa.gov/images/50878/vivid-sunsets-intensify-with-pollution
[5] Young, A. T. (2016). Sunset science. III. Hypotheses on the anomalous twilights. Journal of Quantitative Spectroscopy and Radiative Transfer, 186, 103-115.