Drizzle at sunset results in spectacular pink/red rainbows. Many weather watchers in the UK have been captivated by the sight of rainbows at sunset over the past few days. For some parts of the UK this brought some much-needed colour to dreich summer days. So how do these beautiful rainbows occur?
Pink/red rainbows form in the same way as the usual multicolour ones, from light reflecting off the rear internal surface of water droplets in the atmosphere. However, during sunrise and sunset, rays from the sun travel a longer path through the lower atmosphere. These rays are scattered by air molecules and dust. Shorter-wavelength blues and greens are scattered the most, so the remaining light is richer in longer-wavelength reds and yellows. As the majority of the transmitted light is now in the red spectrum, this is the light seen reflected back from the water droplets, resulting in an almost exclusively pink/red rainbow.
Richard
