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Insider Blog: Red sky at morning sailor take warning; What makes a sunrise or sunset so colorful?

It all starts with air molecules. These scatter light, but they scatter blue light better than other colors thanks to blue's short wavelength. At the other end of the spectrum is red light. This gets scattered last.

At midday, in the summer, the sun is almost directly overhead. This means that the sun's light has relatively little atmosphere to pass through. At this point, the sun's light is pretty equally scattered by all colors.

In the morning and evening, this changes. Because the sun is lower in the sky, the amount of atmosphere that the sun's light has to pass through to get to you is much higher.

Because the light spends more time in the atmosphere, its apparent color begins to change to us here at the surface. Again, because blue light is scattered first, red colors become more dominant.

Season also plays a role in the color of sunsets and sunrises. In the winter, we in the northern hemisphere are tilted away from the sun.

This means there is even more atmosphere for the sun's rays to pass through.

This compounds the effects that were already creating colorful skies in the months closer to the summer solstice.

Lastly, have you ever heard the phrase, "Red Sky at morning, sailor take warning?" There is some truth to this. High pressure to the east can provide more air molecules in the atmosphere for sunlight to pass through, creating a red sky.

This can suggest low pressure, and unsettled weather to the west.

A good test to this rule will be tomorrow's sunrise, as there will be both high pressure to our east and approaching low pressure to our west.

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John Ross

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