system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why Rainbows are curve if light travels in a straight line?

We all know that light follows Rectilinear Propagation and it sometimes bend while diffraction, but i never understand the concept of rainbow and the reason why it is a curve. I have read books and all and everywhere it says that white light passes through raindrops and boom! It is now a circular arc of 7 lights. I understand the phenomenon of refraction and know light of different wavelengths separate when passes through a prism. But after passing through prism, those light travels straight. 

But why is rainbow curve? 🌈
gpt
The rainbow is visible as a curve because it's actually a circle around the sun. Basically the entire sky is scattering light but you can only see the rainbow effect in the part of the sky that forms the correct angle from the sun to the sky to your eye. 

This is also why rainbows move as you do, they're defined by your positional relationship with the sun, as you move that relative position also moves.