Tilting your head while wearing polarized sunglasses can make a rainbow completely disappear or look much brighter.

Rainbows are formed when sunlight undergoes reflection, refraction, and dispersion inside water droplets. During this process, specifically when light reflects off the back of a raindrop at an angle of approximately 42 degrees, the light becomes highly polarized. This means the light waves vibrate primarily in a direction tangential to the arc of the rainbow.Polarized sunglasses are manufactured with a vertical chemical filter to block horizontal glare, such as light reflecting off a flat road or water surface. Because the light from the sides of a rainbow is polarized horizontally, the vertical filters in the glasses can cancel those waves out. When you tilt your head 90 degrees, you change the orientation of the filter relative to the light waves.According to Brewster's Law, named after Scottish physicist David Brewster who proposed it in 1811, light becomes perfectly polarized when it strikes a surface at a specific angle. In a rainbow, the polarization is nearly 100 percent linear. This phenomenon is why photographers use circular polarizing filters to enhance the contrast of the sky or remove reflections from water.If you rotate your polarized lenses so the transmission axis is perpendicular to the polarization of the rainbow, the light is absorbed by the lens material. This results in the rainbow 'vanishing' to the wearer. Conversely, aligning the filter with the light waves makes the rainbow appear more vivid by filtering out non-polarized background noise from the surrounding sky.