Light sky under primary rainbowwhy?

[fisico30]

Hello Forum,
I understand how the primary rainbow is formed: dispersion by water droplets suspended in the air. A single internal reflection takes place. Red color (wavelength) emerges at about 42 degrees with respect to the observer...

but why is the sky below the primary rainbow not showing dispersion? There are water droplets also below the rainbow...It is said that the rays emerger rather horizontally for those droplets...
Perceiving white light means that emerging rays of different wavelengths are more or less overlapping each other..

thanks,
fisico30

 

[mfb]

The drops below the part where you see the rainbow reflect the light with this angle, too. They are visible as part of the rainbow for observers somewhere else.

 

[haruspex]

From the title, you seem to be asking about the bright area below the rainbow. To a large extent it's not so much that this area is bright as that the area of the rainbow is dark. See http://en.wikipedia.org/wiki/Alexander's_band

 

[Andy Resnick]

but why is the sky below the primary rainbow not showing dispersion?

There is- recall that rainbows are an example of a caustic- constructive interference, if you like.

http://www.atoptics.co.uk/fz552.htm

 

[sardar]

Dear fisico30,
Thank you for your question. The reason why the sky below the primary rainbow does not show dispersion is because the angle of incidence of the sunlight is not favorable for the formation of a rainbow. The rainbow is formed when sunlight enters a water droplet at a specific angle and is refracted, reflected and dispersed inside the droplet before exiting at a specific angle. This process is known as total internal reflection. However, the angle at which sunlight enters the droplets below the primary rainbow is not ideal for this process to occur, resulting in a lack of dispersion and the appearance of white light. Additionally, the droplets below the rainbow may be smaller or less numerous, making it difficult for the same level of dispersion to occur. I hope this helps to clarify your question. Thank you for your interest in understanding the science behind the formation of rainbows.