Why is the sky sometimes red at dusk or in the morning?

You might have heard the ancient rhyme ‘red sky at night, shepherd’s delight; Red sky at morning, shepherd’s warning.’ So why does the sky sometimes go red in the morning or at night?

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White light from the sun is made up of lots of different colours of light, all shining at once.

When the sun rises each morning, it shines through the atmosphere to the east of where you are. In Britain, Europe and the USA, our bad weather tends to move from west to east. So, when the sun shines through the atmosphere in the morning and there are clouds on the horizon to the west, they get lit up from underneath by the sun. However, the sun has shone through the atmosphere for a long distance before it reaches those clouds. This means that some of the colours of sunlight are scattered by the atmosphere, so you only see the red, orange and yellow light, making the sky look red. As those clouds are probably heading towards you, that means you might get bad weather later that day. That’s why red sky in the morning is called a shepherd’s warning.

When the sun sets each evening, the sun shines through the atmosphere to the west of where you are. If there are lots of clouds to the west, you will lose sight of the sun when it drops behind the clouds. However, if skies are clear to the west, then sunlight will travel a long way to get to you, meaning it will again look red, orange and yellow. Because skies are clear to the west, then weather the next day will probably be good and shepherds will be delighted.
 

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