eli5 why are rainbows always in a circle or arch shape instead a squiggle or some other shape
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Rainbows are sunlight refracted thru water droplets in the air. The sun emits light in a round shape, so it hits the water in the same way. Depending on the atmospheric conditions, and positions of the sun, the water vapor, and the observer you may see a ring or an arch.
Basically yes. It’s because they are an optical effect emanating from a certain point (the sun) passing through a lens(es) (that is, millions of rain drops) and the appearance is dependent on the point of view of the observer (you).
Because of the geometry of optics, and the reflection and internal refraction of light inside of the individual drops, the rainbow’s shape and position is dependant on the observer and their distance from the rainfall. But it will always appear as a portion of an arc (or a double arc, since the light is actually refracted twice within the raindrops).
This is difficult to explain verbally, so [here](https://i0.wp.com/oikofuge.com/wp-content/uploads/2020/07/rainbow-941×1024-1.jpg?ssl=1) and [here](http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/rbowpri.html) are some decent illustrations.
Rainbows form a ring around the sun, wherever it may be.
Or, possibly more accurately, a ring around the opposite side from the sun. [Diagram.](https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQhAdYX4t-_hop9BDi7Zm8Uh3OVSyfO7K7kIw&usqp=CAU)
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