Rainbow Glints

Last updated on September 16, 2023

Rainbow Glints: A Closer Look at the Phenomenon

Rainbows have captivated humans for centuries with their vibrant colors and ethereal beauty. But have you ever wondered how rainbows are formed? While most of us are familiar with the basic concept of raindrops refracting light to create a rainbow, there is more to this natural phenomenon than meets the eye. In this article, we will take a closer look at rainbow glints and explore the intricate details behind their formation.

When we see a rainbow, what we are actually observing are the glints of colored light from countless individual water droplets. Each drop acts as a tiny prism, dispersing light and creating the stunning array of colors that make up a rainbow. But how exactly does this happen?

The primary bow of a rainbow is formed when rays of light enter a water droplet, reflect off its back surface, and then exit through the side it entered. This process involves two refractions, which cause the light to disperse into its component colors. The result is a beautiful arc of colors stretching across the sky.

However, the phenomenon of rainbow glints goes beyond just the primary bow. Drops of water that glint a particular color at the edge of the rainbow towards our eyes or cameras are situated on or near the surface of a cone known as a "rainbow cone." This cone's apex is located at our eye, while its axis is parallel to the direction of sunlight.

Interestingly, different colors in a rainbow cone have varying widths. The red cone, for instance, is the widest, which explains why the red color appears on the outer edge of the primary bow. On the other hand, the green and blue cones are progressively narrower. As a result, moving water droplets can successively glint different colors to our eyes as they pass through each distinct color cone.

While this explanation provides a simplified understanding of rainbow glints, the reality is more complex. Water droplets actually deflect sunlight rays through a range of angles, leading to a broader distribution of colors. The colors we observe at the rim of the rainbow are those resulting from rays that undergo the least deflection as they pass through the droplets.

To illustrate this point further, let's focus on red rays. The red edge of the rainbow is produced by drops near the surface of the "red cone." However, drops within the cone also direct red light to our eyes, causing any color of the rainbow to be diluted with longer wavelength light. By closely examining individual drops, you may notice some glinting in other colors, adding to the enchanting display of hues.

To truly experience the magic of rainbow glints, one must stand inside a sunlit sprinkler spray and embrace the inevitable soaking. As the water droplets cascade through different color cones, you can witness firsthand the mesmerizing interplay of colors, a testament to the intricate nature of atmospheric optics.

In conclusion, rainbows are not just simple arcs of color; they are a symphony of glints from countless water droplets. Understanding the science behind rainbow glints allows us to appreciate the complexity and beauty of this natural phenomenon. So, the next time you find yourself gazing at a rainbow, take a moment to marvel at the intricate dance of light and water that creates this awe-inspiring spectacle.

Rainbow Glints

Paul Gitto captured this close-up of a rainbow made by a lawn sprinkler.

�Paul Gitto

Images like this show that rainbows are the glints of coloured light from millions of individual water drops.

The primary bow is produced by rays that enter a drop, reflect off the back surface and leave the side of the drop that they entered. The two refractions at the entrance and exit disperse the light into colours.

Drops glinting a particular colour at the rainbow's edge towards the eye or camera are on or near the surface of a cone whose apex is at the eye and axis is parallel to the direction of sunlight - a 'rainbow cone'.

The red cone is widest, producing the red outer edge to the primary bow. The green and blue cones are progressively narrower.

In the image we see the glints of drops frozen in one posion but moving moving drops can successively glint a number of colours to the eye as it falls through each different colour rainbow cone.

It is not altogether that simple because droplets deflect the sun's rays through a range of angles. The colours at the rainbow rim are those from rays undergoing minimum deflection through the drops. There are greater deflection angles too.

If we think only of red rays, the red edge of the bow is produced by drops near the surface of the 'red cone'. Drops within the cone also direct red light to the eye and any colour of the rainbow is diluted with some light of longer wavelengths. Look carefully at the individual drops and you will see some glinting in other colours from the majority.

This is best seen by standing inside a sunlit sprinkler spray and getting very wet!

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Reference Atmospheric Optics

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