I don’t look up enough. When I do, I find myself in awe at how beautiful the sky is. It’s easy to go about our daily lives and accept it as just another constant. Today, I want to ask a question that many of us would have asked before, yet may not have found the answer – why is the sky blue?
From the earliest philosophers to modern scientists, this question has been a journey of discovery that not only explains the physics of light but also the beauty and complexity of our atmosphere, highlighting just how amazing our planet truly is.
Rayleigh Scattering
First, we must learn what Rayleigh Scattering is. Named after the British physicist Lord Rayleigh in the late 19th century, Rayleigh Scattering is the scattering of light by small particles, such as nitrogen and oxygen molecules, in the atmosphere. The visible light spectrum is made up of red, orange, yellow, green, blue, indigo, and violet, each having different wavelengths. When light enters the atmosphere, the nitrogen and molecules molecules scatter shorter wavelengths of light more than longer wavelengths, making them visible across our sky. Since blue and violet light have shorter wavelengths compared to other colours, they scatter more and turn the sky blue.
One question arises from this: If it is the shorter wavelengths that get scattered across the sky most easily, why do we not see violet as often? Violet has the shortest wavelength, so technically we should be seeing violet skies more often than blue or other colours. There are two reasons why blue is the dominant colour. Firstly, some of the violet light gets absorbed by the upper atmosphere, which reduces its visibility. Secondly, our eyes are far less sensitive to violet light than blue, which makes it the dominant colour we perceive.
Imagine a world where the colours of our skies were filled with a sea of colours, regardless of their wavelength. It reminds us that the world we perceive is only limited to what our bodies can comprehend and is limitless with beautiful possibilities.
Sunset and Sunrise
Sunrises and sunsets can become the most beautiful shades of red, orange, and pink. This is due to the light having to travel through more of the Earth’s atmosphere, hence encountering more of the particles that scatter the shorter wavelengths. By the time the light reaches us, a majority of the shorter wavelengths have been scattered, leaving longer wavelengths such as red and orange to dominate the view.
There are other amazing sky phenomena to look out for. Three that you can easily spot are:
Halos
Sometimes you may see a ring around the moon or sun. This is due to the ice crystals in the atmosphere that refract light, creating a beautiful halo effect.
Rainbow clouds
Rainbow Clouds, also known as Cloudbows or Cloud Iridescence, are colourful displays caused by the diffraction of sunlight that travels through clouds. Due to the presence of water droplets or ice crystals in clouds, it transforms the clouds into colourful, almost painting-like, effect.
STEVE
STEVE, short for “Strong Thermal Emission Velocity Enhancement”, is a rare phenomenon that occurs in the atmosphere. A aurora-like streak appears dominates the sky and is associated with strong auroral activity. As STEVE has only recently been identified, it shows just how much is left to learn about our world.
In a Nutshell
Next time you gaze up at the sky I hope you remember the contents of this post. The complex interplay of light, atmosphere and our perception can create a reality worth seeing. By continuing to explore these topics and approaching them with a curious mind, we can appreciate the beauty of our world even more.
Go out there and watch the sunset. When the sky fills with the beautiful reds and oranges remember the tiny molecules scattering the light, the different light wavelengths that made it through, and the incredible journey that light took to reach you to provide this beautiful phenomenon. It makes our world worth exploring.
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