What causes a rainbow to form? It's a relatively simple answer. A rainbow is an optical and meteorological phenomenon that is caused by both reflection and refraction of light in water droplets in the Earth's atmosphere, resulting in a spectrum of colors in the sky. It takes the form of a multicolored arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.
Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind at a low altitude angle. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew. First multiple rays of light enter a drop of water from one direction typically a straight line from the Sun, they then reflect off the back of the drop, and fan out as they leave the drop. The light leaving the drop then a rainbow is spread over a wide viewing angle. A rainbow however does not have a specific starting or ending spot, it all depends on where the observers location is relative to the sun. However the higher the point of view, the fuller the rainbow may become because after all a rainbow is a full circle and not just an arch. For example a mountain climber, may see a fuller rainbow than someone standing in a valley due to his higher viewing point.
The colors that are viewed during the formation of a rainbow are red, orange, yellow, green, blue, indigo and violet, otherwise known as ROYGBIV. There are also 2 kinds of rainbows a single band rainbow and a double rainbow. Secondary rainbows are caused by a double reflection of sunlight inside the raindrops. As a result of the second reflection, the colors of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one.