rainbow  
 

Rainbow(s)

The picture for this spotting differences game was taken on Gran Canaria, the second most populous of the Canary Islands. The photographer has used a wide-angle lens to capture the whole double rainbow above the horizon. The best time to see a rainbow is in the early morning or in the afternoon, when the sun is not at its highest in the sky. This is because a rainbow is caused by reflection, refraction and dispersion of light in droplets of water in the atmosphere. Light enters a drop of water in a straight line from the sun, and reflects off the back of the drop. White light separates into different colours as it enters the raindrop, due to dispersion. Red light is refracted (bent) less than blue light, which emerges at a smaller angle to the original white light ray. This makes violet appear on the inside of the rainbow, and red on the outside . The spectrum, as defined by physicist Isaac Newton, goes: red, orange, yellow, green, blue, indigo and violet. English children learn to remember the order of colours in the spectrum by a mnemonic: “Richard Of York (a king of England) Gave Battle In Vain“. Rainbows can be full circles, but mostly they are seen as arcs, and centred on a line that runs from the sun to the observer.

Secondary rainbows are caused when a double reflection occurs in the raindrops. Secondary rainbows like the one in the photo appear 10 degrees above the primary rainbow, and fainter than it, because their light is spread over a larger area of the sky. The colours of the second rainbow are inverted by the double reflection (as in a mirror), so violet appears on the outside of the rainbow’s arc, and red is seen on the inside.
     
 
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