Rectilinear propagation

Rectilinear propagation means that light travels in straight lines. Just like how you can see in a straight line when you look through a tube, light can also travel straight through space. This is why we can see things that are far away from us, like the stars in the sky. The light they emit travels straight to our eyes. However, if something gets in the way of the light, like a wall or a tree, it can't travel straight through anymore and gets blocked or redirected. So, rectilinear propagation tells us that light travels in a straight line until it is blocked or redirected by something in its path.