Density fluctuations and the color of the sky

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Thread starter pines-demon
Start date May 1, 2024
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Density function Rayleigh Scattering Sky

In summary, density fluctuations in the atmosphere influence the scattering of sunlight, which results in the blue color of the sky. As sunlight passes through the atmosphere, shorter blue wavelengths scatter more than longer red wavelengths due to Rayleigh scattering. Variations in air density, caused by temperature and pressure changes, can enhance this scattering effect, leading to dynamic shifts in the sky's color. This phenomenon explains not only the typical blue hue of the daytime sky but also the variations observed during sunrise and sunset.

May 1, 2024

pines-demon

From posts like this I get that the color of the sky is explained by Rayleigh scattering, but needs density fluctuations. However as atoms are not uniform and are localized, the density is
$$\rho(\mathbf r)=\sum_i \delta(\mathbf r-\mathbf r_i)$$
where ##i## sums over all the atom positions ##\mathbf r_i##. So even if the atoms were ordered and not moving in any way, the average of the density is very different from its deviations, that can be quite large (because there are deltas), and one would still have blue light scattering. Right? The fluctuations are already a given due to the form of the density.

Or do the position of the atoms needs to be correlated but disordered in order for the sky to be blue?

Last edited: May 1, 2024

FAQ: Density fluctuations and the color of the sky

What causes the blue color of the sky?

The blue color of the sky is primarily caused by Rayleigh scattering. When sunlight enters the Earth's atmosphere, it collides with air molecules and small particles. Shorter wavelengths of light, such as blue, are scattered more than longer wavelengths, like red. This scattering causes the sky to appear predominantly blue to our eyes.

How do density fluctuations in the atmosphere affect the color of the sky?

Density fluctuations in the atmosphere, caused by variations in temperature and pressure, can affect the scattering of light. When air density changes, it can alter the way light is refracted and scattered, potentially leading to variations in the perceived color of the sky, especially during sunrise and sunset when the light path is longer.

Why does the sky appear red or orange during sunrise and sunset?

During sunrise and sunset, the sunlight passes through a thicker layer of the Earth's atmosphere compared to when the sun is overhead. This longer path causes more scattering of shorter wavelengths and allows longer wavelengths, such as red and orange, to dominate. This phenomenon is enhanced by particles and pollutants in the atmosphere, which can further scatter the light.

Can pollution affect the color of the sky?

Yes, pollution can significantly affect the color of the sky. Particulate matter and aerosols in the atmosphere can enhance scattering effects, leading to more vivid colors during sunrise and sunset. Additionally, pollution can cause the sky to appear hazier and can alter the overall color perception during the day.

Is the color of the sky the same everywhere on Earth?

No, the color of the sky can vary depending on several factors, including geographic location, weather conditions, and the presence of pollutants or aerosols. For instance, areas with high humidity may experience a different sky color compared to arid regions, and urban areas with significant pollution may have a more muted sky color compared to rural areas.