Posted by: T. Boyd | January 26, 2010

Blue Skies and Red Sunsets

Like the appearance of a rainbow in the clouds on a rainy day, so was the radiance around him. This was the appearance of the likeness of the glory of the Lord. (Ezekiel 1:28)

On our trip to the YMCA today, I asked my grandson why the sky is blue. He said, “Maybe it’s because of the water in the atmosphere.” I replied, “Well that could be part of the reason, but then why is the sky red around the sun at sunset?” He puzzled over that. After a little pause, I gave an explanation and his questions about it helped me clarify the description.

Light, as we described in some articles last year, is made up of small energy bundles called photons. There are red, green, blue photons, and all the other pure colors as well. And sunlight has a mixture of all these colored photons, giving an average to our eyes of white light, or at least it is white in outer space. But our atmosphere affects it in interesting ways.

As the collection of photons of white light passes through the air, the blue photons have about 10 times more chance of being scattered (bouncing off air molecules) than do the red photons. (Today in my research for writing this I found out that Einstein explained this scattering phenomena in 1911 – his contribution to science is amazing, isn’t it?)

Thus the red photons are more likely to pass through the air unimpeded while more of the blue ones bounce off in all directions. Thus when looking at the sky away from the sun, a person will see a mixture of light with more blue photons than red ones, and hence it looks blue – sometimes very blue depending on the sun’s position and the clearness of the air.

On the other hand, as people enjoy a sunrise or sunset, they are looking at the light passing through much more air than when the sun is overhead, so the effect of the blue photons being scattered out is greater, and hence, the direct light from the sun to their eyes or reflecting off the clouds looks red to them.

Why does the moon look larger on the horizon? In fact, it is not larger but is the so-called moon illusion. In fact the width of the moon is exactly the same as it is when it is overhead. On the other hand, the height of the moon on the horizon is actually a little reduced than when overhead, caused by the distortion of the light rays passing through the thicker atmosphere.

There are various theories for the cause of this illusion. The one I like best is that when the moon is near the horizon, our visual system is comparing it to the surrounding scenery, and knowing it is much further away, it seems larger. One article says to “trick your mind out of the moon illusion is to bend over at the waist and look at the moon upside down through your legs” (

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