Partial Lunar Eclipse on October 28, 2023 (Full Moon – Cloudy Night)
 
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Thessaloniki, Tuesday, December 7, 2021, 9:32:04 AM
 

 
The rainbow is a visual phenomenon.
 

It is created by the refraction (refraction) and reflection (reflection) of light in water droplets.

For the rainbow creation it is neccessary to be rain and sun together. The sun must be behind us and the raindrops in front of us

It is a beam of light that contains all 7 colors of the solar spectrum and has an arc shape.

Depending on our position or how high the sun is, we can see part or all of the arc on the horizon. If one is at the top of a mountain or in a tall building, one can see the whole circle.

How is the rainbow formed?

The properties of light and the way it reacts when it passes through raindrops create one of the most striking and colorful phenomena – the rainbow.

The following diagram shows how sunlight behaves when it passes through a drop of water:

Figure 1. Reaction of light when it passes through a raindrop

Source: www.metoffice.gov.uk

The spherical shape of the drops provides the right conditions for the formation of the rainbow.

Because water is denser than air, light passes through the air in the drop more slowly, forming an angle and then changing direction, ie refraction. The light is then reflected internally (internal reflection) at the back of the drop and refracted back to the front as it exits, returning from the water to the air (figure 1).

A beam of light is not white but consists of 7 different colors: Red, orange, yellow, green, blue, indigo and violet.

Each of them has a different wavelength. The direction of the colors with the shortest wavelength, such as blue and violet, is different from that of the colors with the longest wavelength, such as red. The 7 different colors come out of the raindrop with an angle of about 2 degrees between red and violet, which explains the arcuate shape of the phenomenon.

The observer therefore sees specific colors more clearly, with red first (higher in the atmosphere) and violet last (figure 2).

Conditions for the formation of a rainbow

The position of the sun and the raindrops in relation to an observer should be as follows (figure 2):

The sun must be behind the observer

The sun should be low in the sky, at an angle of less than 42 ° above the horizon. This is impossible to do if the sun is too high in the sky. Therefore, the lower the sun, the greater the arc the observer will see.

Rain or other source of water droplets, such as a waterfall or even fog, should be in front of the observer.

Figure 2. Observer position in relation to the rainbow

Source: www.metoffice.gov.uk

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