Bifrost and unweaving the rainbow

Last updated on September 16, 2023

Bifrost: Unweaving the Rainbow and Exploring its Marvels

Rainbows have long captivated the human imagination, evoking a sense of wonder and enchantment. In Norse cosmology, the Universe is depicted as tricentric, with three levels supported by Yggdrasill, the giant ash tree. Connecting two of these levels, Asgard (home of the gods and goddesses) and Midgard (home of mortals), is a flaming rainbow bridge known as Bifrost. This ethereal structure, often visible as our earthly rainbow, is described in the Norse Prose Edda as a "trembling roadway" made with unparalleled skill and cunning.

Contrary to poet John Keats' lamentations about science "unweaving the rainbow," our understanding of the rainbow and its intricate workings only deepens our appreciation for its richness and marvels. Valerio Fontani's breathtaking photograph captured a particularly intense and solid rainbow in Londa, Tuscany, Italy. Its vivid colors are so vibrant that one might be tempted to walk across it.

Let us embark on a journey to unravel the mysteries of this mesmerizing phenomenon, exploring the various elements that compose Bifrost and the rainbow:

1. The Inner Primary Bow

• The inner primary bow forms through a single internal reflection inside raindrops located mostly beyond nearby hills.
• While modern perception often associates rainbows with seven colors, the Vikings believed in three distinct colors. Could they have been onto something?
• Within the primary bow, 2-3 purple and green supernumerary fringes can be observed. These fringes reveal that light behaves as waves, adding an extra layer of fascination to the phenomenon.

2. Faint Bow Extensions

• Closer raindrops create faint bow extensions in front of the hills at the far left and right of the primary bow.
• These extensions, although subtle, contribute to the overall splendor of the rainbow.

3. Rainbow Spokes

• Faint rainbow spokes can be seen deeper inside the primary bow, where small clouds have cast shadows on raindrops that would otherwise contribute to the formation of a complete rainbow.
• These spokes add a touch of complexity to the already intricate tapestry of colors.

4. Reverse Colored Secondary Bow

• Above the primary bow, a fragment of a reverse-colored secondary bow can be observed.
• This secondary bow is created through light reflecting twice inside the raindrops, resulting in a captivating inversion of colors.

5. Alexander's Dark Band

• Between the primary and secondary bows, a dark band known as Alexander's dark band can be seen.
• This band occurs because raindrops cannot refract light in that specific region, creating a noticeable contrast in the sky.

As we delve deeper into the wonders of Bifrost and the rainbow, we realize that these natural phenomena possess a complexity that continues to astonish us. Rather than unraveling their magic, our growing understanding only serves to enhance our appreciation for their beauty. Each discovery brings us closer to comprehending the skill and cunning with which these marvels are crafted.

Valerio Fontani's photograph allows us to witness firsthand the intense and solid nature of this particular rainbow, inviting us to immerse ourselves in its ethereal embrace. The interplay of colors, reflections, and shadows within Bifrost captivates our senses and sparks our curiosity.

Next time you encounter a rainbow, take a moment to ponder the intricacies that lie within. Appreciate its vibrant hues, its subtle fringes, and its elusive extensions. Allow yourself to be transported to a realm where science and wonder intertwine, reminding us of the limitless beauty that exists within our natural world.

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.

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Reference Atmospheric Optics

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