Welcome to You Ask Andy

  Marylou Orr, age 12, of Clayton, Indiana, for her question;

Why does the sun sometimes look white?

One day in May, Marylou looked up and saw a ghostly sun. Instead of a big ball of golden fire, Old Sol had shrunk to a pale white disk. 21 moment later he disappeared behind cloud. The fact is, of course, that the sun itself did not change at all. But before Andy explains what did happen, he has a word of warning for all his young friends who are so interested in what goes on Up There.

It is quite safe to stare at the stars and gaze at the moon. But it is not safe to take even a quick peek at the noonday sun. Remember, Old Sol is an atomic furnace large enough to swallow our whole world a million times :end still have room for dessert. Even though he is some 93 million times away, our eyes are not strong enough to stand his dazzling radiance.

The only safe times to view the sun are at dawn and sunset and on a cloudy day. At such times the sun is veiled with clouds or dense layers of atmosphere. Even so, it is not sensible to stare for more than a few moments,

The sun never changes. It is always a blazing white sphere in the blackness of empty space. If Abel and Baker had seen the sun from the upper reaches of our atmosphere, it would have looked blazing white against a background of black velvety sky. We do not see the sun this way because the dense lower atmosphere filters, bends and changes the color of its rays. Even on cloudless days, the blue rays of sunlight are bent and scattered by the atmosphere ‑ which is why the sky is blue.

Clouds do even more to the rays of sunlight before they reach the ground heavy cloud bounces back three quarters of the sunlight which falls upon its upper surface. Such a cloud is made of droplets of water, maybe almost ready to fall as rain. It casts dark shadows on the ground and hides the sun only when it is directly in front of it.

Clouds made of fine fragments of ice do still stranger things to the sun and to sunlight. These are the high flying cirrus clouds, four to seven miles above our heads. When in the sky at dawn or sunset, cirrus clouds turn radiant hues of red, gold and purple. This happens when the sun's rays slant in a long slope through the atmosphere.

Sometimes cirrus clouds take other forms. They may film the entire sky with a milky veil. At such time we call them cirrostratus, meaning cirrus‑layer clouds. At times the veil is broken into a maze of gauzy scarves, This is most likely the cloud formation which makes the sun look ghostly white to Marylou:

Old Sol had a gauzy veil over his face and a moment later a denser patch of cloud. hid him altogether, The haze and the cloud were most likely made of fine, fine fragments of ice. Such currostratus formations not only dim the sun and moon, they sometimes cause halos to glow around them.


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