The spectrum is formed by the refraction of light as sunlight passes through raindrops or water vapor-mixed air. In this spectrum light is divided into seven colors. These seven colors are violet, indigo , blue , green , yellow , orange and red ; In Bengali these colors are abbreviated with their initials: beniasahkala and in English VIBGYOR. Due to the different wavelengths of light of these seven colors, the amount of curvature varies. For example, the red light bends at an angle of 42. On the other hand, the purple light bends at an angle of 40. Light rays of other colors bend at different angles between 40 ° and 42 . This is why the colors of the rainbow are always seen in a certain row. A little above the initial bright rainbow, a lesser bright rainbow is seen , so that the colors are in reverse order. The sky between these two arches (Alexander's dark region) is a little darker than the rest of the sky , but this difference can be overlooked if not noticed.