atmospheric refraction twinkling of stars night sky is very beautiful it is consists of different objects some of them are stars while others are planets looking at the night sky can you figure out if the object is star or a planet yes you have been learning it from your childhood the objects which twinkle are stars and the objects that do not twinkle are planets the question in today's discussion is why do stars twinkle basically the reason behind the twinkling of stars is atmospheric refraction let's learn how it happens we live on planet earth the atmosphere of earth consists of layers of air the particles of air are closely spaced at the surface of the earth then these at higher layers that means the density of air is highest at the surface while it goes on decreasing towards the top layer now let's talk about a star a star have its own light since they are at far distance from the earth therefore looks point sized and so are treated as point source of light the light coming from star that is a star light when enters in the earth's atmosphere layer by layer it experiences increasing density and so bend towards the normal at the boundaries between the layers when it comes to us we observe the star to be slightly higher than its actual position now air is fluid it have property to flow so there are continuous and random variations in every layer of the atmosphere these changes result in the random change in refractive indexes of the layers so if refractive indices of these layers are not steady how will the apparent position of star appear steady the apparent position changes slightly but randomly similarly because of random changes in refractive indices the brightness of light coming from star also appears to be changing the resulting effect of changing apparent position and changing brightness causes star to appear twinkling [Music] why do planets do not twinkle the reason is simple planets are much closer to earth they reflect light falling on them towards us since planets are much closer to earth they could not be considered as a point sources large number of rays coming from such objects undergo refraction in random manner but while reaching at observer they nullify each other's effect that means neither the position of planet change nor there is change in brightness of light coming from them the intensity of incoming light does not change it remains constant and so planets don't twinkle i hope you have understood this concept very well thanks for watching this video have a look at the range of courses available in variety of formats only on learnft.com