Why does the setting sun sometimes look flatted

A.� Because denser air near the earth's surface causes light to diffract, sometimes presenting a distorted flattened image of the sun.

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Q.� Why are there differences in the earth's atmosphere

A.� The earth's atmosphere becomes increasingly dense nearer to its surface due to differences in composition, meteorological conditions and gravitational pressure.

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The air particles within the earth's atmosphere are subject to two pressures: the compressive weight of the overlying air and the gravitational pull of the earth the closer to the surface they are. Consequently, air particles near the surface are denser, which causes light waves to bend toward the less dense air above.

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Q.� Does this affect the entire image of the sun

A.� No, the lower half of the sun looks flattened while the upper half appears as normal due to the increasing density of the atmosphere.

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The rays of light carrying the image of the sun to our eyes are bent differentially according to the point at which they enter the atmosphere. Those passing the top half of the sun are bent less than those at the bottom half of the sun.

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The top half will project an accurate image, while the bottom half will send an apparent image. Since the bottom portion of the sun is being seen through a thicker, more dense atmosphere, it appears squashed or flattened due to the more intense bending of rays of light.

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Q.� What causes light to refract

A.� Refraction, as defined by Newton, occurs because light changes the speed it is travelling at and bends when it comes into contact with a new medium,�such as water, or a new level of pressure.

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Do you have a question about an apparent natural illusion Click here to ask.

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by Lisa Cardy