While many weather phenomena are awe-inspiring, none have the breathtaking beauty of the rainbow. They are significant to our culture and folklore, and can be found throughout both of them. In 1979, Kermit the Frog sang a song titled ‘The Rainbow Connection’, which was about dreams and wishes. The folklore belief that a pot of gold could be found at the end of a rainbow is well known, but actually originated from an old Irish saying – ‘You are as likely to find to find a pot of gold as you are to find the end of a rainbow’. In short, they appeal to humans’ sense of beauty, magic and wonder.

We see rainbows when the sun strikes a rain shower and the rain reflects the scattered and refracted light back to our eyes. It is a magnificent feat because the phenomenon is occuring through the actions of the sunlight, the rain shower and animals’ and humans’ eyes. Add in a little imagination and this phenomenon is truly spectacular.

Facts about Rainbows

  • A person must be between the Sun and a rain shower to view a rainbow. When a person sees one, they are seeing scattered sunlight that has reflected off of raindrops.
  • The Sun must be less than 42 degrees above the horizon in order for a rainbow to be seen.
  • A rainbow is unique to each person that sees one, as the sunlight reflected from the raindrops is seen at slightly different angles by each person.
  • Rainbows are optical phenomena as well as weather phenomena. Once inside a raindrop, sunlight will undergo 3 different optical phenomena – Dispersion, Refraction and Reflection.
  • When looking for a rainbow, a person should make sure that they can see their shadow. This will point them in the direction of the rain shower and away from the Sun.

What causes a rainbow to occur?

A rainbow is as much an optical phenomenon as it is a weather phenomenon. In order for a rainbow to be seen, the observer of the rainbow must be between the Sun and a rain shower or storm, with the observer facing in the direction of the rain. In addition, the Sun must be lower in the sky – less than 42 degrees above the horizon. Because of this, rainbows are only seen in the morning or afternoon. If the Sun, observer and rain are positioned as such, sunlight from the Sun travels over the observer’s head before it strikes the millions of water droplets in the rain shower. As it strikes each water droplet, 4 events occur that make seeing rainbows possible.

Dispersion. White light is composed of six main colors across a spectrum of different wavelengths. These are Red, Orange, Yellow, Green, Blue, and Violet. When white light strikes a prism, it gets split up into its six main colors. This is known as dispersion. As sunlight, which is actually white light, strikes a water droplet, it also gets dispersed into these six main colors.

Refraction. When light moves from one medium to another, such as from air to a prism or air to water, it changes direction. This is known as refraction. At the same instant the sunlight initially strikes the raindrop and is being dispersed, it is also being refracted.

Reflection. The dispersed and refracted light travels to the other side of the water droplet where it then gets reflected toward the direction it came from but at a different angle.

Refraction. The light travels back towards the side of the water droplet that it entered from. As it exits the water droplet, it again travels between two mediums, water and air, and is refracted once more.

After this process, the dispersed light travels back towards the observer, where it is detected by the observer’s eyes. The rainbow will appear higher in the sky if the Sun is lower in the sky. Conversely, if the Sun is higher in the sky, while remaining below 42 degrees above the horizon, the rainbow will appear lower.

Why do the colors appear in a certain order?

Different wavelengths of light refract at different angles. This is known as Incidence of Refraction. Higher wavelengths of light, such as violet, refract at higher angles. Red, which is at the low end of the visible spectrum, refracts at a lower angle.

When an observer sees a rainbow, all of the water droplets in that rainbow are reflecting the same colors out. Due to the Incidence of Refraction, the observer will only be able to see certain colors from certain water droplets. At the points at the outer edge of the rainbow, the observer views the lowest wavelength color, Red, because the higher wavelength colors reflected from those same droplets were refracted at a higher angle, and went above or outside of the observer’s eyes. At the interior side of the rainbow opposite of the outer points, the observer sees the highest wavelength color, Violet, as the lower wavelength colors from those droplets went below or crossed in front of the observer’s eyes.

It is from this optical phenomenon where the acronym ROYGBIV comes from – the lower wavelength colors of Red, Orange and Yellow are seen at the top of the rainbow, and the higher wavelength colors of green, blue and violet are seen at the bottom.

Why does a rainbow have a bow shape?

Rainbows appear to have a bow shape because the observer is equally distant from the raindrops that are refracting the same wavelengths of light at the necessary angle for that particular wavelength to reach the observer’s eye.

Rainbows in Film and Culture

  • Perhaps the most famous instance of a rainbow in culture is the singing of ‘Somewhere Over the Rainbow’ by Dorothy Gale, played by Judy Garland, in the Wizard of Oz. An extremely popular remake of the song that combined lyrics from the original with lyrics from ‘What a Wonderful World’, was performed by Israel “IZ” Kamakawiwo`ole and released in 1993.