A rainbow is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth's atmosphere.It takes the form of a multicoloured arc,with red on the outside and violet on the inside.A double rainbow includes a second,fainter,arc with colors in the opposite order.
Even though a rainbow spans a continuous spectrum of colours,traditionally the full sequence of colours is most commonly cited as red,orange,yellow,green,blue,indigo and violet.It is commonly thought that indigo was included due to the different religious connotations of the numbers six and seven at the time of Isaac Newton's work on light,despite its lack of scientific significance and the poor ability of humans to distinguish colours in the blue portion of the visual spectrum.[