Here is Part 2 of The Science of Natural Wonders series all about light. It’s pretty essential. From the light that gets us through the day, to beautiful rainbows, and why exactly is the sky blue? This is the science behind the natural wonder that is light.
Let’s start with a fundamental question we’ve all probably heard the answer to as a child; why is the sky blue? Let’s try to get our heads around it this time. Light from the sun is white in appearance but it’s actually made from a rainbow of colours (i.e. visible light), and you can see this rainbow when light is shone through a prism, slowing the light down and separating the colours.
Why do the colours separate? This is due to the wavelength of each colour. Blue light has short waves and red light has longer waves. Light travels in a straight line unless something gets in its way causing it to reflect (like a mirror), bend (like a prism), or scatter (like gaseous molecules in the atmosphere). When sunlight reaches the Earth’s atmosphere, gaseous molecules cause the light to scatter. The shorter, smaller wavelength of blue light causes it to be scattered more than the other colours, meaning that we see the sky as blue, as it is separated from the other colours in light. Why is light at the horizon more white? To reach the horizon the light has been scattered through even more air, re-scattering the blue light further, mixing the colours back together.
What about those beautiful sunrises and sunsets that are just so Instagramable? As the sun is lower for the sunrise/set, the light is passing through more atmosphere to reach us, scattering that blue light even more. This makes way for the red/orange light which creates those picturesque sunsets.
How about rainbows? Why do they happen and why can we see them after rain? Firstly, we can’t see them during a storm (usually) because cloud cover is too great to let any light through. In contrast, hours after rain you won’t see a rainbow either, as all the water vapour in the air has evaporated. So the best time to view a rainbow is right after rain, as the clouds are clearing, because we need the presence of water vapour and sunlight. Similarly, with the prism or atmosphere, when white sunlight hits a raindrop, the speed of the light is slowed and scattered (i.e. refracted) into the rainbow of colours dependant on wavelength. Within the raindrop, after being refracted, the light is then reflected until it exits the raindrop. Two rainbows are created during the process. The second is usually fainter, and sometimes barely visible, but will appear above the brighter rainbow and is inverted as the light has undergone reflection twice.
The below picture was taken at Gullfoss waterfall in Iceland this year, where we spotted many rainbows and even walked right through one!
Knowing all this science, what have researchers done to utilise it? Fibre optics are a great example. They consist of a very thin rod of glass or plastic. Light is shone into one end and the fibre reflects the light multiple times (i.e. total internal reflection) until it reaches the other end of the fibre and can exit.
This technology is used for high-speed broadband and cable TV. Information you need to transmit can be converted into signals in numerous ways. For optical fibres this is done by converting the information into visible or infrared light, and it is these pulses of light which carry the information. Fibre optics can carry information much faster than traditional copper cable telephone lines. They can also carry more information, and the signals do not fade across longer distances. The same science that causes rainbows, sunsets and the sky to be blue, also provides us with high-speed WiFi. You have to love nature.
Light is essential and there are many more applications than just fibre optics, but I’ll save them for another post. Without these natural wonders, we may not have such high speed internet and we certainly wouldn’t get to enjoy rainbows after a storm. Next time you take a snap of a gorgeous sunset, try to remember why it happens, enjoying both nature and the science behind it.