What is the main characteristic of Rayleigh scattering?

Rayleigh scattering is characterized primarily by the fact that the size of the scatterers—typically molecules or small particles—is much smaller than the wavelength of the incident radiation. This phenomenon involves light interacting with particles whose sizes are less than about one-tenth the wavelength of the light being scattered.

When the wavelength of the incident radiation is similar to the size of the scatterers, the scattering process deviates from Rayleigh scattering and can be described by different scattering theories, such as Mie scattering. Therefore, the main characteristic of Rayleigh scattering hinges on the size relationship, which is critical for understanding how shorter wavelengths of light (like blue light) are scattered more than longer wavelengths (like red light), leading to the blue appearance of the sky.

This distinction sets Rayleigh scattering apart from other potential scattering mechanisms and is specifically why the correct answer emphasizes the relationship between the wavelength and the scatterer size, focusing on the condition that it is much smaller than the wavelength.