A primary rainbow is brighter than a secondary rainbow and has colors changing from red on the outside to violet on the inside.

We will focus on two raindrops to explain why this color pattern develops. Red light from the higher drop is directed toward the observer's eyes, while violet light is directed at a level above the observer.

From the lower drop, red light is directed to a level below the line of sight, while violet light is seen by the observer. This is why the colors of a primary rainbow change from red on the top of the arc to violet on the bottom.

how they develop

Terms for using data resources. CD-ROM available. Credits and Acknowledgments for WW2010. Department of Atmospheric Sciences (DAS) at the University of Illinois at Urbana-Champaign.

secondary rainbow