Every primary rainbow you’ve ever seen displays the same angle-of-arc. If there’s a rainbow that the Sun is creating, looking exactly opposite to the direction of the Sun and look for a circle (or portion of a circle) that’s offset from that direction by 42° will enable you to see it. The reason is simple physics: light behaves as a ray, the speed of light in water is different than the speed of light in air, and when light enters or leaves that medium, it always bends in a predictable way determined by the angle-of-incidence at the interface between the water and the air.When light moves from air into water, different wavelengths bend at slightly different angles, causing the colors to disperse. When light strikes the back of the water droplet (and it’s a very good assumption that all droplets are perfectly spherical), it reflects at a known, predictable angle. And when it re-emerges back into the air, each wavelength moves off at a specific angle-of-offset from the original: from just under 41° to a little under 43° over the visible light spectrum, with the peak intensity occurring at 42°.When light transitions from vacuum (or air) into a water droplet, it first refracts, then reflects off of the back, and at last refracts back into vacuum (or air). The angle that the incoming light makes with the outgoing light always peaks at an angle of 42 degrees, explaining why rainbows always make the same angle in the sky.