Here's how it works:
* The Earth is a sphere: The Earth's curved surface means that the horizon isn't a flat line.
* Distance and perspective: When the sun is low on the horizon, it's very far away. Because of the curvature of the Earth, hills or mountains appear to rise up and block the sun from our view.
* Optical illusion: Our brains interpret what we see based on our understanding of the world. We expect hills to be solid objects, and we see them "blocking" the sun. However, the sun isn't actually being blocked by the hills; it's just that our perspective makes it appear that way.
Think of it this way: Imagine you're standing on a beach looking out at the ocean. The water appears to meet the sky at a horizon. But we know the Earth is round, so there's no actual point where the water "ends" and the sky "begins". It's just an optical illusion created by our perspective.
The same concept applies to the sun appearing behind hills. It's an illusion caused by the Earth's curvature and our perception of how the world works.
