![]() In summary, I think the sky would be much darker (factor of 50) and would have a much redder spectrum. I think that this would enhance the relative redness of the scattered light a bit more, but given that the incoming flux at 700 nm is similar to that of the Sun, it wouldn't increase the sky brightness. This scattering is much less wavelength dependent, depends on the size distribution of the particles and is much stronger for small scattering angles. The optical depth to scattering can be dominated by particulates in the atmosphere at wavelengths above 600 mm. The net effect would be that the sky was much darker, and rather than being dominated by blue light, would actually have a redder spectrum (what colour this would be perceived as, I'm not sure).īut Rayleigh scattering isn't the only thing going on. ![]() The overall amount of scattered red light would be about the same as in the solar case, but the amount of scattered blue light would be reduced by about a factor of 50. If Rayleigh scattering was all that was going on, and the total flux incident at the top of the atmosphere was the same, then the scattered spectrum from the red giant illumination would be quite different. A red giant has a spectrum that peaks at around 900 nm (in the infrared), and the flux is about 100 times lower at 400 nm and two times lower at 700 nm (which is why they are called red giants). The solar spectrum peaks at about 500 nm and is about a factor of two less intense at both 400 nm and 700 nm. However, the spectrum of light that is being scattered is very different in the case of a red giant. Some numbers are that the optical depth at zenith, from sea level is about 0.36 at 400 mm (blue) and ten times smaller at 700 nm ( Bucholtz 1995). On the contrary, there is sufficient optical depth to scatter some blue light, even if it arrives from the Sun at zenith. On Earth, the atmospheric optical depth to Rayleigh scattering is very small at red wavelengths, so hardly any red light is scattered, even at sunset when the Sun is viewed through a thick atmospheric layer. Rayleigh scattering happens at all wavelengths, but the scattering cross section goes as $\lambda^$.
0 Comments
Leave a Reply. |