The sun and moon, celestial bodies that have captivated human curiosity since time immemorial, are the subject of numerous studies and anecdotes. Among these, one phenomenon that has garnered considerable interest is their appearance against a transparent background, or more scientifically, when they arenot obstacles for, but originate behind, the line of sight.
In such instances, the sun and moon do not merely provide light and darkness, but also offer unique optical effects that have been the subject of awe and contemplation throughout human history. Unbeknownst to many, these effects are subject to the principles of optics, physics, and even our perception of these celestial bodies.
The Sun's Transparency
The sun, a yellow dwarf star, is often associated with its overwhelming brightness. However, under rare conditions, it can appear transparent. This phenomenon, known as a 'green flash,' occurs when Earth's atmosphere separates the light of the sun and bends it, causing the sun's last light to glance off the atmosphere and present as a brief green flash just as it disappears below the horizon.
Green flashes don't occur at all sunsets, but when they do, they are usually too quick to perceive thouroughly. Nevertheless, for those lucky enough to observe one, the experience can be highly rewarding, filling one with a sense of awe at Nature's serendipitous capabilities.
Types of Green Flashes
There are two main types of green flashes: inferior and superior. The inferior green flash occurs when the weather is calm with clear skies. This results in the light being less diffused, producing a consistency of the color throughout the flash. On the other hand, the superior green flash occurs in adverse weather conditions due to atmosphere instability. This produces a variety of colors reflected in the flash, including reds, yellows, and greens, but the latter is the most common and striking.
The green flash is an elusive phenomenon that has been recorded by sailors and scientific expeditions, yet it cannot be fully explained due to its dependency on specific atmospheric conditions. However, the fact that it is an optical illusion plays a crucial role in understanding its occurrence.
The Trappist-1 Solar System
An interesting research question in the field of astronomy involves the potential transparency of the sun in exoplanet systems. In 2017, NASA announced the discovery of seven Earth-sized planets orbiting the ultracool dwarf star TRAPPIST-1. Among these, three planets are in the habitable zone, raising speculation about potential transparency effects similar to that of the green flash.
Further research in this area, although still purely theoretical, could yield significant implications for the understanding of both astrophysics and astrobiology. Nevertheless, the possibility of sun transparency under different planetary conditions offers a fascinating prospect for future exploration.
The Moon's Transparency
The moon, although not capable of shining on its own, can create intriguing transparency effects, particularly during a lunar halo or a moon dog. These occurrences happen when moonlight passes through ice crystals in the atmosphere, refracting and reflecting the light and creating a ring or multiple images around the moon.
Lunar halos and moon dogs are often visible during winter (°C) conditions due to the presence of high, thin clouds consisting of hexagonal ice crystals. The moon's light is refracted by these crystals, creating the illusion of rainbow-colored circles or 'moon dogs' around the moon.
Observing a lunar halo
Witnessing a lunar halo, or 'moon ring,' is a spectacular experience. It appears as a ring around the moon caused by refraction in ice crystals in the Earth's atmosphere. The size of the halo depends on the thickness of the clouds and can vary significantly. They are typically white but can also appear as colored halos under specific atmospheric conditions.
Lunar halos have been used for navigational purposes in the past, with navigators estimating their distance from the moon based on the size of the halo. Today, they serve primarily as a bench for scientific study of the atmosphere and an exciting spectacle for astronomy enthusiasts.
The Supermoon illusion
The 'supermoon' illusion, sometimes referred to as a 'wolf moon,' occurs when the full moon is at its closest point to Earth in its elliptical orbit, appearing larger and brighter than usual. This can create an illusion of transparency or 'super' clarity due to the lot of light and closeness of the moon itself.
The Supermoon illusion presents a captivating and charming spectacle, adding to the folklore and mysteries that have surrounded the moon for centuries. Despite its engagement in fascinating optical effects, the moon remains a constant and familiar companion, a source of wonder and inspiration for humans.
Understanding the sun and moon's transparency phenomenon stands as a testament to the intricacies of our planetary system and the universe at large. As we continue to delve deeper into these celestial mysteries, from green flashes to exoplanet sun systems, one thing is certain: our cosmos remains ever full of wonder, waiting to be explored.