Since the beginning of recorded history, humans have gazed in wonder at the beautiful phenomena that occur in the skies above them. Atmospheric imagery such as rainbows, ice halos and other tricks of the sun’s light have gone on to inspire legends and folktales, as well as some of the greatest artwork in human culture. While these optic events in our atmosphere are truly a sight to behold, most of us may not fully understand the science behind what makes them occur.
In-depth knowledge about our atmosphere is usually only required of scientists who are tasked with studying and forecasting atmospheric events, such as meteorologists. While this may be the case, these days it is important that everyone develop an appreciation for our atmosphere, especially as it becomes increasingly endangered by our reliance on pollutants. Therefore, having a basic scientific understanding and appreciation for the beauty of our atmosphere can also be the first step in combating the carelessness that may one day destroy it.
The Science Behind What We See in the Sky
Some of the most common optics that determine what we see when we look to the sky are rays and shadows created by sunlight and tiny particles in the air. The gorgeous rays of light we see shooting down to Earth from the clouds are known as crepuscular rays. These are caused by sunlight being filtered by clouds, dark particles or objects, such as mountains, that may be blocking certain areas of the sun’s light stream.
Shadows, on the other hand, are sort of the opposite of crepuscular rays, in the sense that they project a stream of darkness as opposed to light. Most of us know that shadows are caused by placing an opaque object in front of a light source, and this is also the case with shadows that occur in our atmosphere. Cloud shadows are perhaps one of the most common types of shadows we see made by the atmosphere, and are typically visible in wide open flat lands and deserts, often after a period of heavy rain.
In addition to the small and large particles in the air that lead to the creation of crepuscular rays and shadows, water droplets in the clouds and atmosphere also cause some pretty amazing effects. Condensation in the air that has yet to become heavy enough to turn into rain floats around and within clouds as tiny ice crystals, creating a beautiful, multi-colored effect when combined with direct sunlight. One example of this is the rainbow-like corona we see around the sun when it shines through a particularly dense (but mostly invisible) sheet of water droplets in the air.
Rain is caused by the merging of water droplets into heavier droplets that eventually fall from the sky as they get too heavy to float. Rainbows result from rays of light being shot through these raindrops as they fall, which then become refracted in very much the same way as the rings of multi-colored light created by water droplets in the atmosphere. The difference with rainbows, however, is that as rain falls to the ground, the multi-colored bands of light that are created are pulled back up towards the sun, creating a dome shape from two points on the ground. While there are several different types of rainbows, the classic dome-shaped, or primary rainbow, is perhaps the most well-known.
Halos in our atmosphere have sparked reactions that have ranged from intense fear to religious ecstasy. Similar to the effect water droplets have on the sun’s light in our atmosphere, halos are caused by ice crystals forming in cirrus clouds that refract light in a more intense fashion than their unfrozen counterparts. The primary difference between halos and coronas is that the latter is often very small and forms closely around the circumference of the sun itself, while halos create a much larger circle around the light source. These ice halos, also known as 22° halos, can be seen around the sun or the moon, and have been inspirational to human art and spirituality for eons.
Some of the most spectacular optics we can witness in the sky are visible from higher altitudes – where the air is thinner and fewer objects block the sun’s rays. As one goes higher into the Earth’s atmosphere, clouds and light take on a very different form than what we are able to discern at sea level. Known as the high atmosphere, those of us lucky enough to reach these heights in the sky will be rewarded with some amazing examples of how light bends and refracts with little to no blockage from particles and objects that would normally kept these effects hidden from our view on the ground.
About 300 miles above the Earth, majestic solar events, such as the aurora (more famously, the aurora borealis in the Arctic) can be seen flowing across the sky. Auroras, also known as northern or southern lights, are visible from dusk to dawn and are caused by solar storms that can normally only be seen very close to either the north or south poles. These storms are visible from these locations as a result of a combination of electromagnetic energy produced by the two poles, as well as the incredibly thin atmosphere that makes the viewing of these gorgeous light shows possible.
While learning about the science behind everyday beauty, such as atmospheric optics, may have little value outside of the realm of atmospheric science and meteorology, having a detailed understanding of many of the optics we see above and around us everyday can be both fun and rewarding. Not only does gaining this knowledge help increase our appreciation of the science behind our beautiful skies, it can also serve as a great conversation piece during your outdoor adventures with family and/or friends. Next time you’re out and about, be on the lookout for these wonderful sights created by our atmosphere and show off a bit of the great knowledge you managed to learn about them along the way.