Why it happens
The rainbow, which in Latin is arcus pluvius, means “rainy arch” and is a meteorological phenomenon caused by reflection, refraction, and dispersion of light in water droplets in the atmosphere which results in a spectrum of light appearing in the sky.
It was believed that the earliest occurrence of the rainbow was in the Bible, Genesis Chapter 9, as a sign of God’s covenant to never destroy the earth with a flood again. The ancient Greek and Romans believed that rainbows were a path Iris, the goddess of rainbow created to link humans to the mortals.
Rainbow can be full circles of light. However, most people see only an arc formed by illuminated droplets above the ground and centered on a line from the sun to their eyes. The most commonly visible and remembered colors are Isaac Newton’s sevenfold red, orange, yellow, green, blue, indigo and violet. The acronym ROYGBIV – Richard Of York Gave Battle In Vain is a good way to remember the sequence.
Many forms of airborne water can cause a rainbow to appear which include rain, mist, airborne dew and sea spray.
In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This is because the light is being refracted when entering a droplet of water, it then reflected inside on the back of the droplet and refracted again when leaving it.
In a double rainbow, a much fainter arc is seen outside of the primary arc. This happens as a result of light bouncing inside the water droplet more than once before escaping, causing the spectrum of the second arch to be reversed with red on the inner side of the arc.
Other types of Rainbows are:
This is a very rare rainbow; it appears as two rainbow arcs that split from a single base. The colors in the second bow appear in the same order as the primary rainbow rather than reversing as in a secondary rainbow.
The sunlight is first deflected by the raindrops and then reflected off the body of water, before reaching the observer. The reflected rainbow is frequently visible, at least partially, even in small puddles. A reflected rainbow may appear in the water surface below the horizon.
Monochrome or Red Rainbow
Monochrome is rare form or rainbow that happens when there’s a shower at sunrise or sunset, colors like blue and green at the shorter wavelength are scattered and removed from the spectrum.
Lunar Rainbow or Moonbow
A lunar rainbow or “moonbow” is rare; it is produced by light from the sun and also the moon. It as white to an observer even though all colors are faintly present.
Fogbows form in the same way as rainbows, but they are formed by much smaller cloud and fog droplets that diffract light extensively. They are almost white with very faint colors visible. Fogbows can be seen anywhere the fog is thin enough for a bright sun to shine through. They are much larger and broader than rainbows.
Rainbow colors have been in use as flags for centuries. In the 16th century, it was a symbol of the Cooperative movement in the German Peasants’ War, now for LGBT Social Movements, of peace in Italy, and of gay pride.