3 replies to this topic

[Krukarius]

Probably everyone noticed, that the sky even during partial solar eclipse looks different than in typical conditions. I consider especially the eclipses with magnitudes smaller than 0.5, when the solar center is still uncovered by the Moon. The sky looks vibrant, slightly in pale blue, but intriguingly with slight shift towards red giving eventially some reddish mixture. Now, let's consider the case. Since the Rayleigh scattering is inversely proportional to the fourth power of the wavelength (1/λ4) the most scattered light is blue and violet. As some amount of sunlight is blocked, the proportion of scattered wavelengths is disturbed. In practise, we shall see smaller number of short wavelengths scattered in accound of longer wavelengths, which value decreases also, but in smaller amount. 
Could anyone explain how does it work exactly? I not mean the limb darkening, because this effect comes through when at least the center of solar disk is blocked. Where could I read more about it? Honestly I couldn'tg find anything explaining phenomenon this way, therefore I am asking.

[triplemon]

As some amount of sunlight is blocked, the proportion of scattered wavelengths is disturbed. 

Why would the spectral properties of the sunlight change, in particular if the moon covers less than half of the suns disk ? Even limb darkening is mostly a reductioon of the amount of light due to the view angle, but not so much a change in the spectral properties of that light.

And why would the scattering in earths atmosphere change ? Its the same light, still coming from the same direction, the same air that scatters it.
 

I never noticed any change in light or sky color during an eclipse this early, not even when much closer to totality. Granted, lighting conditions look notably unusual, as you normally only experience dimmed sunlight near sunset, when atmospheric absorption filters the light to be much more red. Photographers call it golden hour. While during an eclipse its not filtered red despite being reduced in amount greatly. So it looks cooler/bluer compared to what you expect from daily experience.

Edited by triplemon, 25 March 2025 - 04:53 PM.

[KMH]

Check out this link:

 

https://www.cloudyni...-to-limb-color/

 

Gordon did measure a color shift during annularity for the October 2023 eclipse.  But this only applied when all of the sun except for the limb was covered.

 

Kevin

[Krukarius]

Why would the spectral properties of the sunlight change, in particular if the moon covers less than half of the suns disk ? Even limb darkening is mostly a reductioon of the amount of light due to the view angle, but not so much a change in the spectral properties of that light.

And why would the scattering in earths atmosphere change ? Its the same light, still coming from the same direction, the same air that scatters it.
 

I never noticed any change in light or sky color during an eclipse this early, not even when much closer to totality. Granted, lighting conditions look notably unusual, as you normally only experience dimmed sunlight near sunset, when atmospheric absorption filters the light to be much more red. Photographers call it golden hour. While during an eclipse its not filtered red despite being reduced in amount greatly. So it looks cooler/bluer compared to what you expect from daily experience.

I was (un)fortunate to notice it, but not directly by the naked eye. I've noticed them by the camera, once compared my images with non-eclipse conditions.

Moreover in the link below I found something, which I would agree with:

https://astronomy.st...se-respectively

 

They say, that until the Sun's disk center is blocked the ambient light is a bit bluer. When the solar center is blocked by the Moon, then limb darkening becomes crucial and finally the scene experiences sunlight shifted towards red. In fact it's still limb-darkening, but the red sihf I could spot even during partial solar eclipse of 2022 having just 39% disk covered in Poland.