Rayleigh scattering is a phenomenon that occurs when light waves interact with particles or molecules that are much smaller than the wavelength of the light. It is named after the British scientist Lord Rayleigh, who first described the phenomenon in the 19th century. Rayleigh scattering is responsible for the blue color of the sky during the day and the reddish hues seen during sunrise and sunset.
The scattering of light occurs because the electric field component of the light waves interacts with the charged particles in the medium. In the Earth's atmosphere, these particles are primarily nitrogen and oxygen molecules. The amount of scattering is inversely proportional to the fourth power of the wavelength of the light. This means that shorter wavelengths (blue and violet light) are scattered more than longer wavelengths (red and orange light).
Key points about Rayleigh scattering:
Blue sky: During the day, sunlight contains a range of colors. However, shorter wavelengths of light, particularly blue and violet, are scattered more by the atmospheric particles. This leads to the sky appearing predominantly blue to an observer on the Earth's surface.
Reddish colors at sunrise and sunset: When the sun is low on the horizon during sunrise or sunset, the sunlight has to pass through a larger portion of the Earth's atmosphere. This results in increased scattering of shorter wavelengths, allowing more of the longer-wavelength red and orange light to reach the observer. As a result, the sky takes on warm hues during these times.
Polarization: Rayleigh scattering is more effective for shorter wavelengths and is also strongly polarized. This polarization is responsible for the polarization patterns observed in the sky.
Dependence on wavelength: The intensity of Rayleigh scattering is inversely proportional to the fourth power of the wavelength. This means that shorter wavelengths are scattered more efficiently than longer wavelengths.
While Rayleigh scattering is a fundamental process that explains many atmospheric optical phenomena, it is not the only scattering mechanism at play. In some situations, especially when the size of the scattering particles is comparable to the wavelength of light, other scattering mechanisms, such as Mie scattering, become more significant.