Ask The Science Experts

Actually, the intensity of the stars themselves doesn’t fluctuate, rather it is the light they emit that appears to brighten and dim as it passes through the air in our earthly environment. Were you to look at the stars from an airless environment, say the moon, you would see them as solid luminous points of light.

So why does the air make them appear to twinkle? Basically, our atmospheric air is constantly moving, with warm air masses constantly rising and cool ones sinking. The densities of these masses is different and thus the refractive (light bending) characteristics are also different. So when starlight passes through thinner air, then thicker, then thinner again, it bends accordingly and appears to shimmer.

Now you may wonder, if light passing through our atmosphere refracts like this, why don’t planets seem to twinkle? It’s because the planets are much much closer to Earth than are the stars. We actually see planets as tiny disks rather than single points of light. The light from planets will still be bent, but since we see it as a “disk,” it is made up of many points of light. Each of them may brighten and dim as they pass through our atmosphere, but the average intensity of these points of light is fairly constant.

Source: How Come? by Kathy Wollard. Posted by admin for educational and science toys.

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