Plz explain why rainbow has that kind of arc form and..?

Question

what decides the size of it?

Answer 1

it is light refracting throw water in the air each person will see a different look to the rainbow because It is a moving atmospheric event.

The mist refracts the water to your eye and the color are roygbiv. The ligth hits the mist cloud and refacts to the ground.

I hope this helped.

Answer 2

Rainbows are actually circular in shape. If you were in an airplane flying above you would see a complete circular rainbow. Standing on the ground you can only see part of it because the rest of it is going beyond the horizon. The size is dependant upon how high up above the earth it is. The higher up the larger the circle will be.

Answer 3

because the earth is round.