Rainbows have captivated human imagination for centuries with their vibrant colors and ethereal beauty. These awe-inspiring optical phenomena occur when sunlight interacts with raindrops in the atmosphere, creating a stunning display of colors. While most of us are familiar with the classic rainbow that arches across the sky, there are actually two types of rainbows: low and high rainbows. In this article, we will explore these two fascinating variations and delve deeper into their unique characteristics.
At sunrise or sunset, the center of a rainbow, known as the antisolar point, aligns with the horizon. This gives rise to a semicircular rainbow that appears to be half in the sky. As the sun rises or sets, the position of the antisolar point changes, causing the rainbow to shift in relation to the horizon. When the sun reaches an elevation of 42 degrees, only the tip of the bow is visible above the horizon. This means that during the summer months, when the sun is higher in the sky, rainbows are best observed in the early morning or late afternoon when the sun is relatively low.
While we are accustomed to seeing rainbows arcing across the sky, there is a hidden spectacle that occurs below the horizon. Parts of a rainbow can often be seen against a backdrop of fields or the ground, creating a mesmerizing sight. From elevated vantage points such as mountains or even from aircraft, it is possible to witness a more complete circle of a rainbow. This phenomenon adds an extra layer of enchantment to the already captivating display.
To truly appreciate the splendor of low and high rainbows, it is essential to understand the underlying physics. When sunlight enters a raindrop, it undergoes refraction, bending as it passes from air to water and again as it exits the drop. The light also undergoes reflection inside the raindrop, bouncing off the inner surface before exiting. These processes cause the white light to disperse into its component colors, creating the familiar spectrum of colors in a rainbow.
The angle at which sunlight is deviated inside a raindrop determines the size and shape of the resulting rainbow. For low rainbows, the angle of deviation is approximately 42 degrees. This means that the light exiting the raindrop forms an angle of 42 degrees with the incident sunlight. As a result, low rainbows appear to be centered on a point directly opposite the sun, with their tips just a few degrees above the horizon.
Various atmospheric conditions can influence the visibility of rainbows. The presence of raindrops in the air is, of course, essential for rainbow formation. However, other factors such as the size of the raindrops, their distribution, and the angle of sunlight also play a role. When raindrops are small and well-distributed, they create a vibrant and distinct rainbow. Conversely, larger raindrops or uneven distribution can lead to a less defined or even faint rainbow.
The elevation of the sun is a crucial factor in determining the visibility and appearance of rainbows. During sunrise or sunset, when the sun is near the horizon, low rainbows are more likely to be observed. As the sun rises higher in the sky, the antisolar point descends, causing the rainbow to shift downwards. Eventually, when the sun reaches an elevation of 42 degrees, only the top portion of the bow remains visible above the horizon.
The position and visibility of rainbows can vary depending on the observer's latitude. At the equator, where the sun is nearly overhead year-round, rainbows are more likely to be observed in their entirety. In contrast, at higher latitudes, where the sun's elevation is lower, rainbows may appear more fragmented or even incomplete. Understanding these variations adds an additional dimension of wonder to the study of rainbows.
Capturing the beauty of low and high rainbows through photography can be a rewarding endeavor. To photograph a low rainbow, it is best to find a vantage point that offers an unobstructed view of the horizon. This allows for the inclusion of the atmospheric landscape, enhancing the overall composition. High rainbows, on the other hand, can be photographed from elevated locations such as mountains or from the window of an airplane. Experimenting with different angles and compositions can result in breathtaking images that showcase the magnificence of these natural phenomena.
Beyond their scientific allure, rainbows hold significant symbolism in various cultures around the world. Often associated with hope, renewal, and unity, rainbows have been featured in myths, legends, and religious texts throughout history. Their appearance after a storm is often seen as a sign of better times to come, inspiring feelings of optimism and joy. The universal appeal of rainbows transcends cultural boundaries, reminding us of the profound beauty and interconnectedness of our natural world.
In conclusion, low and high rainbows offer a fascinating glimpse into the captivating world of atmospheric optics. These enchanting optical phenomena, shaped by sunlight and raindrops, create awe-inspiring displays that have captivated humanity for generations. Understanding the science behind rainbow formation and the factors that influence their visibility enhances our appreciation for these natural wonders. So next time you find yourself gazing at a rainbow, take a moment to marvel at its intricate beauty and contemplate the magical interplay of light and water that brings it to life.
Rainbow at Mylor Harbour, Falmouth, Cornwall UK imaged by Linda Bennett at 14:45 local time on March 28, '07. Only the top of the bow peeks above the sea. Rainbows are about 42° in radius and centered on a point directly opposite the sun - the 'anti-solar point'. Here the sun was 39° high and so the anti-solar point was that distance below the horizon. The Rainbow tip was therefore only 42-39 = 3° above the horizon. Image ©Linda Bennett, shown with permission.
At sunrise or sunset a rainbow's centre, the antisolar point, is on the horizon. The rainbow is half in the sky, a semicircle. As the sun rises the bow's centre sinks. Eventually when the sun is 42º high only the tip of the bow is visible above the horizon. In the summer, rainbows are best seen in early morning or late afternoon when the sun is comparatively low.
Parts of a bow can often be seen below the horizon against a backdrop of fields or the ground. A more complete circle is sometimes visible from mountains or aircraft.
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"Low and High Rainbows". Atmospheric Optics. Accessed on November 30, 2023. https://atoptics.co.uk/blog/low-and-high-rainbows/.
"Low and High Rainbows". Atmospheric Optics, https://atoptics.co.uk/blog/low-and-high-rainbows/. Accessed 30 November, 2023
Low and High Rainbows. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/low-and-high-rainbows/.