Bifrost, the rainbow bridge Valerio Fontani saw this at Londa in Tuscany, Italy. Some rainbows are elusive, some fragmented, some faint. This one is so intense, so solid, that you might walk across it.? BIFROST In Norse cosmology the Universe is tricentric with three levels supported by Yggdrasill the giant ash tree. A flaming rainbow bridge, Bifrost, connects two levels, Asgard home of the gods and goddesses, and Midgard, home of mortals. ?Bifrost, that �trembling roadway�, is sometimes visible as our rainbow. In the great Norse Prose Edda it is written:?�You will have seen it but maybe you call it the rainbow. It has three colours and it is very strong, and made with more skill and cunning than other structures�.?It certainly is made with skill and cunning - we are still discovering its subtleties. Unlike poet Keats� oft quoted grumbles about science 'unweaving the rainbow', the more curious we are and the more we understand the rainbow and nature then the more we see, appreciate and treasure their richness and marvels.? Valerio's inner primary bow forms from a single internal reflection inside raindrops. They are mostly beyond the nearby hills. Closer raindrops form faint bow extensions in front of the hills at far left and right. Throwing away modern prejudice that bows have seven colours, were the Vikings equally correct in asserting there are three??Just inside the primary are 2-3 purple and green supernumerary fringes. They tell us that light behaves (sometimes!) as waves.?Deeper inside are faint rainbow spokes where small clouds have shadowed otherwise rainbow forming raindrops.?Above the primary is a fragment of reverse coloured secondary bow. Light reflected twice inside the raindrops to make it.?Between the primary and secondary the sky is darker. Alexanders dark band. Raindrops cannot refract light there.??