Water Aureole Imaged by Andrew Kirk on Easter Sunday 23rd March. ©Andrew Kirk, shown with permission. The ever-shifting surface of water is full of optical effects. Here, ripples on the water surface act as lenses to direct converging cones of light downwards. When water is slightly turbid they become visible but not as you might expect. The light cones are all parallel to each other but perspective effects make them appear to radiate outwards from the point directly opposite the sun where the shadow of your head is located. Where the focused light shines on the streambed it forms a moving pattern of bright curves - caustics. Watch them carefully to see gem-like flashes of colour as the water lenses re-image them. Rays and perspective effects