You're Probably Wrong About Rainbows

Rainbows are curved due to the maximum scattering angle of light reflecting off raindrops, which varies by color. The phenomenon is a unique optical illusion for each observer, dependent on their position relative to the sun and the raindrops, and can be altered using polarized sunglasses. Understanding this complex phenomenon highlights the value of learning by doing, rather than memorizing facts, fostering deeper understanding of the natural world.

Rainbow Formation

• 00:00:07 Rainbows require sunlight, raindrops, and an observer. Light entering a raindrop refracts and reflects off the back surface before exiting, with different colors having different maximum scattering angles. This concentration of light rays at specific angles forms the rainbow's curved shape, with red having the largest angle and violet the smallest.

Refractive Index

• 00:01:37 Light slows down when entering a denser medium, such as water or glass, due to interactions with charges within the material. These interactions create a phase kick that shortens the wavelength and bends the light, which is explained by Snell's Law. The refractive index is the ratio of the speed of light in a vacuum to the speed in the medium.

Polarized Light

• 00:17:31 Sunlight is unpolarized, but when light reflects off a raindrop at Brewster's angle, it becomes polarized. Rainbow light is polarized horizontally at the top and more vertically at the sides, which is why polarized sunglasses can make a rainbow disappear or appear brighter.

Double Rainbows & Alexander's Dark Band

• 00:19:14 A double rainbow occurs due to a second internal reflection within raindrops, producing a fainter rainbow with inverted colors. The region between the two rainbows, known as Alexander's dark band, is darker because no light reflected once or twice inside the raindrop exits at those angles.

Supernumerary Rainbows & Glories

• 00:20:42 Supernumerary rainbows are multiple rainbow-like bands under the primary rainbow and result from interference of light rays when raindrops are small. Glories, or Brocken bows, are also due to interference, requiring even smaller droplets and producing smaller circles of color around the observer's shadow.