hi friends i'm sure you know the nursery rhyme twinkle twinkle little star how i wonder what you are but do you know why do stars twinkle that's exactly what we are going to explore in this video and we'll also look at other interesting things such as why do stars seem higher than they actually are and do you know that we can see the sun rise two minutes before the sun actually comes up the horizon and similarly we can see the sun even two minutes after the sunset and as usual we'll finish off this video with our top three questions on this topic let's start with our twinkle twinkle little star i'm sure you've seen the stars twinkling in the night sky but do you know that if you're an astronaut and you go into space you'll see that the stars no longer twinkle they are like beautiful little bright dots in the black sky then why do stars twinkle on the earth that's right it's due to the earth's atmosphere the atmosphere refracts the light coming from the stars which causes a twinkling effect so the twinkling of stars is due to atmospheric refraction but before we look at the details let's take a look at a different but simpler example let's say you're standing near a bonfire and if you look at the things through the hot air above the fire what do you notice can you see that the lights above and behind the fire are flickering they seem to be shivering why the air just above the fire is hot and it's less dense compared to the cooler air above and around it the refractive index of the hotter air is slightly less than the refractive index of the cooler air so the light coming from the bulbs will refract the light will bend but the layers of air are constantly shifting they are not stationary so the light coming from the bulbs keeps refracting randomly and this gives us a flickering effect these flickering lights are at a close distance from the fire now let me turn the camera and show you some lights that are on a building far away if you carefully look at these tiny lights above the fire can you see that these small lights seem to be twinkling just like stars the air above the fire is hot and it's less dense compared to the cooler air above and around it the refractive index of the hotter air is slightly less than the refractive index of the cooler air so the light coming from the bulbs will refract the light will bend but the layers of air are constantly shifting they are not stationary so the light coming from these far away bulbs keeps refracting randomly the path of the light from the far away bulbs keeps changing so the amount of light entering our eyes keeps changing as a result the bulbs sometimes appear brighter and sometimes dimmer to us this bright dim bright dim effect gives us a twinkling effect similarly we can explain the twinkling of stars the atmosphere is made up of many many layers the layers are at different temperature the cooler layers are more dense compared to the warm layers so the atmosphere is made up of many layers having different optical density now when we look up at the stars the light is coming from the star when light enters the atmosphere it undergoes refraction because light is going from vacuum to the atmosphere as we discussed the atmosphere is made up of many layers having different densities the bending of light also takes place at the boundaries of these layers so the light from the star that reaches our eyes has gone through many many refractions if we trace back the light the star is at a different position from its actual position as you can see the apparent position of the star is higher than its real position and this takes place due to atmospheric refraction but remember the layers of the atmosphere are constantly shifting and changing so the refraction of light is continuously changing and the apparent position of the star keeps fluctuating the path of light coming from the star is constantly changing and so the amount of light that enters our eyes keeps changing as a result the star appears brighter sometimes and sometimes dimmer to us this bright dim bright dim effect makes us think that the star is twinkling now an interesting question is the stars twinkle but why the planets don't appear to twinkle that's right the planets are much closer to us compared to the stars so they appear quite big to us if you look at the star it's like a tiny point source of light but the planet in comparison is a much larger source of light an extended source of light so variations in light coming from the planet are not noticeable to us so the planet does not appear to twinkle as we learnt the twinkling of stars is caused by atmospheric refraction now let's look at another interesting phenomena caused by atmospheric refraction early sunrise and delayed sunset do you know that the sun is visible to us two minutes before the actual sunrise so even though the sun is just below the horizon we can still see it similarly the sun is visible to us two minutes after the actual sunset once again even though the sun is just below the horizon we can still see it after the sunset now let's take a look how this magic takes place imagine you're standing on a beach eagerly waiting for the sunrise waiting for the sun to come up the horizon what does horizon mean horizon is the line at which the earth's surface and sky appear to meet horizon is best visible when you're looking towards the sea the horizon is basically the line of the water here now let's zoom out from this scene and look at you standing on the earth it would look something like this imagine you're standing on the earth like me and looking at the sunrise if there was no atmosphere we would be able to see the sun only after it came up the horizon but the layers of the atmosphere cause refraction of light the sunlight is passing from less dense to more dense layers of air as shown here the light is bending towards us and it reaches our eyes so we are able to see the sun even though it's actually below the horizon this is the apparent position of the sun that's why we can see an early sunrise about two minutes before the actual sunrise similarly in the evening the sun is setting in the west at sunset the sun goes below the horizon once again the sunlight is going from less dense to more dense layers of air so multiple refractions are taking place here and as you can see the sunlight bends towards us and reaches our eyes so we are able to see the sun even though the sun is actually below the horizon but this is the apparent position of the sun so we can see the sun even two minutes after sunset so thanks to atmospheric refraction how much is our day longer by that's right two plus two four minutes two minutes during sunrise and two minutes during sunset so our day is longer by four minutes due to atmospheric refraction let's place the different phenomena due to atmospheric refraction on our concept board twinkle twinkle little star now we know how you twinkle as we discussed in this video twinkling of stars the higher position of a star an early sunrise and delayed sunset these are all optical illusions optical illusions due to atmospheric refraction to watch more science and maths videos like this do check out my website manochacademy.com links are given below the video and do remember to subscribe to my youtube channel and follow my facebook page thanks for watching to try these features and learn more about the course just go to my website manoj academy.com to make it easy i'll put the links below hope you like it and happy learning