At a music festival this summer, I noticed a group of people raising their phones in the air – reaching towards something. Everybody around them was watching a band on a stage a little way off, but this cluster had turned their backs to the music and were gazing, intently, somewhere beyond the boundary of the park. I looked out over my neighbour’s shoulder and saw a rainbow above the horizon.

We had all seen rainbows before, and this one was nothing special. Why were these people trying to capture it on their phones when they could have been watching a band they had paid to see? Perhaps they were interested in the science of the interaction between water and