Have you ever wondered why do stars twinkle instead of emitting a light of constant brightness? Common beliefs include that of "Stars are like sun, a ball of fire, therefore as the stars burn, the flames from the fire dance around and cause the stars to twinkle", but most of us would doubt the credibility of such explanations.

To explain why a star twinkles, let me use an analogy here. You fill up a bowl with water, and then submerge a coin into it. Use a finger to generate some water waves as you look at the coin through the water. You would probably see the image of the coin wobbling side to side through the ripples because water in the bowl refracts the path of light from the coin.

This is similar to how light travels from the star to our eyes. Most stars are very far away from us, well outside our Earth’s atmosphere. Our atmosphere is very turbulent, with streams and eddies forming, churning around and dispersing all the time. These moving pockets of hot and warm air act like lenses with different optical density, distorting and refracting the light from the star as it passes through the many layers of the Earth’s atmosphere before it reaches our eyes.

Image taken from http://www.enchantedlearning.com 

As a result, we perceive this continuous random refraction of the light (see picture) as "twinkling" of the stars. In contrast, if we view the same stars in outer space, we will not be able to observe the "twinkling" effect simply because there isn’t any atmosphere.

So, now that you know what causes stars to twinkle, can anyone make an intelligent guess why planets do not "twinkle" when viewed from Earth?