Double Rainbow, Why?

A double rainbow
In the UK, after having such warm and dry period of weather at the start of spring, and over the last couple of years a reduced level of rainfall leading to the South East of England being declared in a draught, with reservoirs at all time low levels, the last few days of April has been cold and wet, with some areas having record rainfall.
The sky turns black, blacker than I have seen for a longtime, and the rain comes down, and yet, typical of UK weather, the dark clouds soon pass, and we find ourselves in sunshine. 
We call this weather April Showers.
So here we are, the dark cloud passes over in the early evening, yet to the west, the setting sun is in a cloud free sky, the result was another rainbow, not just one but a double rainbow.
I have never seen or realised there could be a double rainbow, so typically, I needed to know what causes this natural show.
A rainbow is caused by the light from the sun passing through the raindrops, resulting in a multicoloured arc. The light as it enters the droplets is refracted, split into the seven colours of the spectrum of light, as the picture above shows, being red, orange, yellow, green, blue, indigo and violet, with blue on the inside and red on the outside.
The process as the sunlight passes through the water droplets is that the light is refracted as it enters the droplets, then it is reflected back from the opposite side of the inside of the droplet, and as the light passes out of the droplet it is refracted again.
This was first described by Sir Isaac Newton, 1642 to 1727.
A double rainbow is a secondary arc outside the primary arc, and the colours are reversed, so the blue is on the outside, and is caused by the light being reflected twice within the droplets.
Now I know.

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