In the last few topics you sent light through a prism — one solid block of glass with sharp faces. Here the "glass" is the whole atmosphere above your head, and it is not one block. It is built of layers, and that one change is what bends starlight on its way to your eye.
1. Present the physical scene
Picture this. It is a clear, dark night in your village, far from any street light. You look straight up. The sky is full of stars, and they are not sitting still — each one is shivering, flickering, getting a little brighter and then a little dimmer, again and again. People say the stars are "twinkling."
Now picture the morning. You are awake before dawn near a field. You look east. The sky is glowing, and then the top edge of the Sun appears over the horizon. By the clock, sunrise is supposed to be at, say, 6:00. But you are seeing the Sun a couple of minutes before 6:00. And in the evening, the Sun seems to hang at the horizon even after it should have set — as if it is late to leave.
Stop scrolling. Try it in your head before reading on. The star is a huge, steady ball of fire, lakhs of times bigger than Earth. So why would its light shiver on the way to your eye? Is the star itself flickering, or is something happening to its light in between?
(Answer: the star is not flickering. The star is steady. What shivers is its light on the way down to you — as it passes through the air above your head. The air is the troublemaker, not the star. That is the whole secret of this topic.)
You can now name the scene we are about to explain: starlight and sunlight do not travel through empty space all the way to your eye — they pass through the atmosphere first, and the atmosphere bends them.