Drawing a rainbow in AI

When I started learning AI, I soon learnt to use the gradient tool because I was involved in writing a photodermatology review that required a figure of an electromagnetic spectrum. This inspired me to draw a rainbow for fun but I just couldn't find a way to do it with the gradient tool. Finally I realised last night I knew how to do it. First apply a radial gradient to a circle. Next draw a rainbow shape with two circles and a rectangle using the shape builder tool. Then finally make a clipping mask and there is the rainbow.