In my research of clouds and sunsets, one feature stands out above the rest: the color red. There is a simple scientific explanation for why clouds turn red as the sun sets.
Sun set is at 8:44 pm:
8:41 pm (3 min before sunset)8:47 pm (3 min after sunset)
How light travels through the atmosphere
We all know the sky is blue, and you may know that the entire sky appears blue because blue light scatters throughout the atmosphere. All light scatters and the first wavelength to scatter is blue. White light contains all wavelengths of light. Light travels in a straight line, and when the blue light scatters away, the remaining colors continue straight, and it is no longer a white light. This is why you end up with orange and yellow at sunset. Red light does not scatter nearly as much as other wavelengths, so the final color remaining is red. Red only happens after official sunset time, when the sun is beyond the horizon.
December 24, 1968, Apollo 8 astronaut William Anders
During the day, the Sun shines light straight down through the atmosphere - except along the edges. Along the edges of daylight, light is traveling at an angle, even at a tangent skimming the surface of the earth, never touching the surface and traveling in and out of the atmosphere. This gives the light much more time in the atmosphere for different wavelengths of light to be subtracted as some scatter into our atmosphere.
When this light - minus blue - hits clouds, it reflects different colors depending on how much light has scattered away. Most light must scatter away to reveal a vibrant red, so the light must travel a maximum distance. You have probably heard that more polluted air creates a better sunset - and this is partially true. The scattering of light is due to particles and molecules scattering the sunlight. However, the main ingredient for atmospheric color is the amount of time that the sunlight spends in the atmosphere The atmosphere can be more or less effective at scattering light based on certain properties. It is more effective at scattering light when fine particles like volcanic ash are in the atmosphere. Volcanic eruptions can send particles into the stratosphere - more than 31 miles up - creating a much larger area of the atmosphere that is actively scattering the light passing through. Standard pollution levels in the atmosphere will scatter the light for only the bottom 30 miles, and mostly near the surface where air pressure is highest. This is why you can generally expect yellow and red in your sunset, but only expect to see purple under special circumstances. In a polluted area with low winds, you end up with just a haze near the surface known as smog. If light were traveling through a small, densely polluted, isolated air mass, that wouldn't contribute to a beautiful sunset.
November 13, 2020, Alex G Perez twitter: @agpfoto
There are many things to note about this pyrocumulus cloud formed by a rocket launch. First, near the surface the dark clouds are dark because they are in the shadow of the earth! Sunlight is not able to hit the surface or these clouds. Above that, we can see red where light has traveled at a tangent, the greatest distance through the atmosphere. Above that is orange, where blue light has scattered but yellow and red light remain. Very high up, near the top of this cloud it is white; this is because at such great altitudes the atmosphere is very thin, with less air molecules and particles to cause any scattering - the sunlight hits this part of the cloud directly.
8:51 pm (7 min after sunset)
If there is anything practical to learn from this, it is that if you are on a boat, and you see red clouds in the sunset, you better be headed home or else be out on the water at night! If red is in the sky, the sun has already set!
Also, an ideal place for a sunset would be Hawaii. There is the lowest horizon possible on earth all around you - the Pacific Ocean. There is low light pollution. There is volcanic activity and high-atmosphere pollution. For a photo, you can get a vantage point high on a mountain, which further lowers your horizon, allowing you to observe a greater section of atmosphere.
layout: post title: Sunset Science: The Color Red preview: https://github.com/murdockfpv/murdockfpv.github.io/blob/master/images/2021-06-07/2021-06-07-2047.jpg?raw=true thumbnail: https://github.com/murdockfpv/murdockfpv.github.io/blob/master/images/2021-06-07/2021-06-07-2047.jpg?raw=true tags: sunset; clouds
Sun set is at 8:44 pm:
How light travels through the atmosphere
We all know the sky is blue, and you may know that the entire sky appears blue because blue light scatters throughout the atmosphere. All light scatters and the first wavelength to scatter is blue. White light contains all wavelengths of light. Light travels in a straight line, and when the blue light scatters away, the remaining colors continue straight, and it is no longer a white light. This is why you end up with orange and yellow at sunset. Red light does not scatter nearly as much as other wavelengths, so the final color remaining is red. Red only happens after official sunset time, when the sun is beyond the horizon.
During the day, the Sun shines light straight down through the atmosphere - except along the edges. Along the edges of daylight, light is traveling at an angle, even at a tangent skimming the surface of the earth, never touching the surface and traveling in and out of the atmosphere. This gives the light much more time in the atmosphere for different wavelengths of light to be subtracted as some scatter into our atmosphere.
When this light - minus blue - hits clouds, it reflects different colors depending on how much light has scattered away. Most light must scatter away to reveal a vibrant red, so the light must travel a maximum distance. You have probably heard that more polluted air creates a better sunset - and this is partially true. The scattering of light is due to particles and molecules scattering the sunlight. However, the main ingredient for atmospheric color is the amount of time that the sunlight spends in the atmosphere The atmosphere can be more or less effective at scattering light based on certain properties. It is more effective at scattering light when fine particles like volcanic ash are in the atmosphere. Volcanic eruptions can send particles into the stratosphere - more than 31 miles up - creating a much larger area of the atmosphere that is actively scattering the light passing through. Standard pollution levels in the atmosphere will scatter the light for only the bottom 30 miles, and mostly near the surface where air pressure is highest. This is why you can generally expect yellow and red in your sunset, but only expect to see purple under special circumstances. In a polluted area with low winds, you end up with just a haze near the surface known as smog. If light were traveling through a small, densely polluted, isolated air mass, that wouldn't contribute to a beautiful sunset.
There are many things to note about this pyrocumulus cloud formed by a rocket launch. First, near the surface the dark clouds are dark because they are in the shadow of the earth! Sunlight is not able to hit the surface or these clouds. Above that, we can see red where light has traveled at a tangent, the greatest distance through the atmosphere. Above that is orange, where blue light has scattered but yellow and red light remain. Very high up, near the top of this cloud it is white; this is because at such great altitudes the atmosphere is very thin, with less air molecules and particles to cause any scattering - the sunlight hits this part of the cloud directly.
If there is anything practical to learn from this, it is that if you are on a boat, and you see red clouds in the sunset, you better be headed home or else be out on the water at night! If red is in the sky, the sun has already set!
Also, an ideal place for a sunset would be Hawaii. There is the lowest horizon possible on earth all around you - the Pacific Ocean. There is low light pollution. There is volcanic activity and high-atmosphere pollution. For a photo, you can get a vantage point high on a mountain, which further lowers your horizon, allowing you to observe a greater section of atmosphere.