I understand that when electromagnetic waves from sun hit/interact with the particles(charges) in the sky, the particles also oscillate with the same frequency of sunlight and hence radiate(scatter) their own electromagnetic waves. And since blue electromagnetic wave has highest energy, it makes the particles oscillate in their frequency more, compared to other frequencies.

Here is what Im confused about.

Since sunlight consists of all different frequency waves (which hit the air particles at the same time), then do the air particles interact with all the frequency waves at once?

If they interact with all of them at once, then shouldn't they oscillate at a single frequency, which is produced by combination of energies from all waves?

Or do they oscillate seperately at all frequencies corresponding to the spectrum of sunlight?

(Im finding it hard to explain my question correctly, if its confusing please let me know, I will edit it :D )

  • 2
    $\begingroup$ en.wikipedia.org/wiki/Rayleigh_scattering $\endgroup$
    – anna v
    Commented Jan 23, 2023 at 6:42
  • $\begingroup$ I think the different colours of light correspond to different frequency/energy photons which indeed travelling together (without really superimposing) and behave as superimposed when they interact with the particles or charges. Thus, the particle oscillates at the combination of all photon energies, and radiates accordingly. Still not clear why small wavelength is radiated more though? And why after all photons are absorbed, the radiation emitted is blackbody(ish)? $\endgroup$ Commented Jan 26, 2023 at 15:42

1 Answer 1


The oscillation of interacting molecule largely depends on the wavelength, type of scattering, size of molecule, and type of molecules/material.

Why sky is blue? Because of its lower wavelength and higher energy in sunlight spectrum, it scatters more. That means it dominates in interacting with air particles/molecules.

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Other than that, different molecules, materials, or atoms act differently for different wavelength/frequency of radiations as this property is really uselful in spectroscopy.

The most common nitrogen and oxygen molecules in atmosphere are most effective in scattering the higher frequency and shorter wavelength portions of the visible light.

A molecule can also oscillate at multiple frequencies simultaneously due to interactions with other molecules or external radiation. As a molecule have rotational and vibrational energy levels, and can therefore oscillate at multiple frequencies corresponding to these different energy levels and transition rates of its internal degrees of freedom.

Molecules that scatter from the light, with wavelength much larger than the size of the molecule, oscillates at a single frequency, which is the same as the frequency of the incoming light. (Rayleigh scattering)

If the wavelength of the light is similar to the size of the molecule, the molecule oscillate at a different frequency than the incoming light and does not oscillate at a single frequency. (Raman scattering)

The light is scattered by particles that are larger than the wavelength of the light has a different frequency than the incoming light. (Non-selective scattering)

  • $\begingroup$ Is this also affected by the vibrational modes of the atomic bonds of the molecule or does that only play a role for absorption/emission? $\endgroup$
    – Redirectk
    Commented Jan 24, 2023 at 20:20

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