A RAINBOW is "one of the most spectacular light shows observed on earth". Indeed the traditional rainbow is sunlight spread out into its spectrum of colors and diverted to the eye of the observer by water droplets. The "bow" part of the word describes the fact that the rainbow is a group of nearly circular arcs of color all having a common center. It is not uncommon to see a rainbow behind or ahead of a rain storm, but have you ever seen a double rainbow?
DOUBLE-RAINBOW: According to meteorologists, a ray of sunlight passes through a raindrop, reflecting off the back of the drop at varying angles. Along with this reflection is refraction of light that causes of a spectrum of colors-- red, orange, yellow, green, blue, indigo and violet. Certain angles and "bending" reflect light better for refraction to occur, and the amount of light refraction corresponds to wavelength and color.
For example, blue light is always refracted at a deeper angle than red light. This is the reason blue is found at the inside of the bow and red on the very outside. Nature's natural color spectrum always elicits the same pattern (red, orange, yellow, green, blue, indigo, violet) when light is refracted, commonly known from the Roy G. Biv mnemonic.
While a primary rainbow is visible when light is reflected once off the back of a raindrop, a secondary and usually dimmer rainbow is spotted when light is reflected twice in a more complicated pattern. The colors of the second rainbow are inverted, with blue on the outside and red moved to the inside. The second bow appears dimmer or cloudier because much more light is released from two reflections, and both bows cover a larger portion of the sky.
It is rare and unlikely, but three or even four rainbows can be seen on occasion, but only if they are reflected off of the earthly objects. The best time to see a rainbow is in the early morning or late afternoon, when the sun is lower in the sky. When the sun is in a lower position, a higher bow can be seen. Rainbows are actually a full circle, but we only see the top bow because the bottom half is below the ground. Many rain droplets of all different sizes, not just one, are responsible for this phenomena. Perhaps billions of water droplets and sunlight reflections make a rainbow visible to the human eye.
HOW ARE THE COLOR OF THE RAINBOW FORMED:
The traditional description of the rainbow is that it is made up of seven colors - red, orange, yellow, green, blue, indigo, and violet. Actually, the rainbow is a whole continuum of colors from red to violet and even beyond the colors that the eye can see.
The colors of the rainbow arise from two basic facts:
1. Sunlight is made up of the whole range of colors that the eye can detect. The range of sunlight colors, when combined, looks white to the eye. This property of sunlight was first demonstrated by Sir Isaac Newton in 1666.
2. Light of different colors is refracted by different amounts when it passes from one medium (air, for example) into another (water or glass, for example).