A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth’s atmosphere. They take the form of a multicoloured arc, with red on the outer part of the arch and violet on the inner section of the arch.
Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind a person at a low altitude angle. The most spectacular rainbow displays happen when half of the sky is still dark with clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background.
The rainbow effect is also commonly seen near waterfalls or fountains. The effect can also be artificially created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow, lunar rainbow or night-time rainbow, can be seen on strongly moonlit nights. As human visual perception for colour is poor in low light, moonbows are often perceived to be white.
A rainbow does not actually exist at a particular location in the sky. Its apparent position depends on the observer’s location and the position of the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer’s eye. This light is what constitutes the rainbow for that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior.
The Irish leprechaun’s secret hiding place for his pot of gold is usually said to be at the end of the rainbow. This place is impossible to reach, because the rainbow is an optical effect which depends on the location of the viewer. When walking towards the end of a rainbow, it will move further away.
In Greek mythology, the rainbow was considered to be a path made by the messenger Iris between earth and heaven. In Chinese mythology, the rainbow was a slit in the sky sealed by the goddess Nuwa using stones of five different colours. In Hindu mythology, the rainbow is the bow of Indra, the God of lightning, thunder and rain. After Noah’s Flood, the Bible relates that the rainbow gained meaning as the sign of God’s promise that terrestrial life would never again be destroyed by flood.