A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky. It takes the form of a multicolored circular arc. Rainbows are seen when there are water drops in the air and sunlight shining from behind the observer through the drops at a low altitude angle. Rainbows are formed when light from the sun is reflected and refracted by water droplets suspended in the atmosphere. Inside each raindrop, light is reflected off the back of the drop and refracted on its way out. This causes different wavelengths of light, corresponding to different colors, to separate and become visible to the human eye in the process.
What causes a rainbow?
Rainbows are optical phenomena caused by reflection, refraction and dispersion of sunlight by raindrops. For a rainbow to form, several conditions have to be met:
| Condition | Explanation |
|---|---|
| Sunlight | Sunlight provides the light needed to form a rainbow. Sunlight is made up of various wavelengths corresponding to different colors. |
| Rain | The water droplets in the air from rain act like small prisms that refract and disperse the sunlight. |
| Observer angle | The observer must have their back to the sun with the rain/water droplets in front of them at a low altitude angle (typically 40-42 degrees). |
When these conditions are just right, the light entering the raindrop is refracted and reflected, then dispersed as it exits in a spectrum of colors. Red light with a longer wavelength is bent least while violet light with a shorter wavelength is bent the most. This creates the multicolored rainbow arc we see in the sky.
Rainbow optics
The optical process that creates a rainbow involves three key steps:
- As sunlight enters a raindrop, it is refracted and dispersed into its component colors and wavelengths.
- The different wavelengths of light are then reflected off the back inner surface of the raindrop.
- When the light rays exit the raindrop, they are refracted and dispersed again into the colors of the rainbow.
Inside the raindrop, dispersion separates sunlight into individual wavelengths. Shorter wavelengths corresponding to violet and blue bend more than longer wavelengths of red and orange. When the dispersed light reflects off the back of the raindrop, the light rays are refracted again when exiting. This separates the light into the visible color spectrum.
The observer’s angle in relation to the sun’s position determines where in the sky the rainbow will appear. The center of the arc is always directly opposite the sun. Since rainbows form a circular arc centered on the anti-solar point, the rainbow is always observed at a 40-42 degree angle from the sun.
Rainbow colors
A rainbow displays a continuous spectrum of colors from red to violet. While it may appear to have seven distinct color bands, there is actually a limitless number of hues blended seamlessly. The seven main rainbow colors as seen from the inner to outer arc are:
- Red
- Orange
- Yellow
- Green
- Blue
- Indigo
- Violet
Red has the longest wavelength visible to the human eye while violet has the shortest. The sequence of colors is determined by the amount of refraction of each wavelength inside the raindrops. Shorter wavelengths are bent more than longer wavelengths as they reflect and exit.
There are also secondary rainbows that can sometimes be seen outside the primary rainbow. These secondary bows have the order of their colors reversed, with violet on the inner part of the arc and red on the outside. They are caused by a double reflection of sunlight inside the raindrops.
Rainbow myths and legends
Throughout history and across human cultures, rainbows have been the source of many myths, folktales and legends. Some common rainbow myths and beliefs include:
– In Greek mythology, the rainbow was considered to be a path made by the messenger goddess Iris.
– In Hindu mythology, the rainbow is called Indra Dhanush, meaning Indra’s bow. It was said to be the bow of Indra, the god of lightning, storms and rain.
– In Irish folklore, leprechauns were said to have hidden pots of gold at the ends of rainbows.
– Some cultures believed rainbows had healing powers and being under one could cure illnesses.
– There is a myth that if you dig under where a rainbow meets the ground you can find a pot of gold.
– Some legends say that rainbows signify good fortune after a storm. Spotting a rainbow is considered lucky in many cultures.
– In some Native American tribes, rainbows represent the union between spiritual and earthly realms.
– The Bible story of Noah’s Ark describes God creating the rainbow as a sign of his covenant to never again destroy the earth with a flood.
Rainbows in art and culture
Rainbows have inspired artists, musicians, writers and pop culture across the centuries and around the world:
– Rainbows are depicted in many famous paintings and artworks, including Vincent Van Gogh’s “Cafe Terrace at Night” and Paul Signac’s “Rainbow, Paysage du Cap Croisette”.
– The rainbow flag is a symbol of LGBT pride and diversity first popularized in the 1970s.
– “Over the Rainbow” sung by Judy Garland in The Wizard of Oz is one of the most famous songs featuring rainbows.
– Rainbow Brite was a popular cartoon character and doll with rainbow-colored hair in the 1980s.
– Rainbows are featured prominently in New Age beliefs and psychadelia-inspired art.
– Tech companies like Apple and Google have used rainbow themes and logos to represent diversity.
– The triple rainbow is a popular internet meme stemming from a viral YouTube video.
When can rainbows be seen?
Rainbows can be seen whenever the right conditions occur together:
– Rainbows only form when the sun is shining while it is raining. The rain provides the water droplets and the sunshine provides the light needed.
– Rainbows are usually seen in the late afternoon around sunrise or before sunset. The sun has to be at an angle of 40-42° to the observer for a rainbow to appear.
– The best time to see rainbows is when a rain shower is moving away and the sun is behind you emerging from the clouds.
– Rainbows can happen any time of the year but are more common during the rainy spring season.
– Rainbows are sometimes seen near waterfalls, sea spray or lawn sprinklers due to the water mist in the air.
– You can increase your chances of seeing a rainbow by having a good vantage point like top of a hill or overlook.
– You can occasionally see rainbows on very humid, drizzly days even without rain due to sufficient mist.
Double rainbows
Sometimes a secondary, fainter rainbow can be seen outside the primary rainbow arc. This is called a double rainbow and it is caused by a double internal reflection and refraction within the raindrops. In a double rainbow:
– The secondary rainbow will be at an angle of 50-53° from the anti-solar point, outside the 42° primary bow.
– The order of colors in the secondary bow is reversed, with red on the outside and violet on the inside.
– The secondary bow is fainter and has less well-defined bands of color compared to the primary.
– A very bright primary rainbow will have a more visible secondary rainbow, due to more light being reflected twice.
– Other variations like triple and quadruple rainbows with multiple reflections can also occasionally be observed.
– Moonbows, rainbows produced by moonlight rather than sunlight, sometimes display double rainbows at night.
Conclusion
In summary, rainbows are beautiful meteorological phenomena that have fascinated humankind across cultures and history. They are optical illusions caused by the refraction, reflection and dispersion of sunlight through rain droplets. Their multicolored arcs are always observed at around a 42 degree angle from the sun when it is raining with the sun behind the observer. Rainbows have inspired legends, myths, art and pop culture symbolizing luck, miracles, spirituality and diversity. These optical spectacles never fail to delight when their colorful arcs suddenly appear in the sky following a rainstorm. The next time you are caught in the rain, be sure to look for rainbows lighting up the horizon. You may just glimpse the elusive pot of gold at the end of their colorful rays!
