7. Exercises VII

1. Why do stars twinkle?

 

Stars emitabsorb their own light but due to the atmospheric reflectionatmospheric refractionatmospheric dispersion of light, they appears to shine. They are considered as extended sources of lightpoint sources of light as stars are nearvery far away from the earth. When the light coming from stars enters into the earth’s atmosphere, it gets dispersedrefractedreflected at same levelsdifferent levels due to the change in density of air at different levels of the atmosphere. When the starlight refracteddispersedreflected by the atmosphere reaches closer to us, it appears brighterdarker than while it was far from us.

 

Due to this effect, it appears as if the stars are twinkling at night.

 

2. Explain why the planets do not twinkle?

 

Planets are relatively closer torelatively far away from earth as compared to stars. As they appear smaller in sizelarger in size than that of stars, planets can be considered as a collection of a large number of extended sources of lightpoint-size sources of light. The various parts of these planets generate a same intensity of lightdifferent intensity of light in such a manner that the average of brighter and dimmer effect is highzero. Therefore, the planets don’t appear to twinkle.