Why is the sky blue?
Scientists tell us that the sky takes on its familiar blue coloration due to the refraction and reflection of light off of tiny particles, such as dust, pollen, and water vapor, which are quite abundant in the earth’s atmosphere. Of course, we all know the real reason that the sky is blue: If it were green, we wouldn’t know where to stop mowing.
A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight. The white light from the sun is a mixture of all colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.
The sun is a very bright source of light. The light passes through atoms of nitrogen and oxygen, the gases that make up most of the air in the atmosphere. As it passes through, the light scatters and the blue part of the sunlight scatters most. At sunset, however, as the sun sets over the horizon the blue light is not in our line of sight, and we see other colors that make up sunlight. These can paint the sky red and orange.
Parents and teachers have traditionally made up lots of reasonable explanations. Adults are supposed to know the answers to such simple questions, right? Unfortunately, all of the explanations that I have ever heard are at least partly incorrect. The correct answer is: Only because of a remarkable coincidence. The Earth’s atmosphere is primarily made of Oxygen and Nitrogen. It happens that both these are made up of atoms of about the same size. It also turns out to be true that EVERYTHING has lots of empty space between and around the atoms that it is made of. Our Sun produces light which is actually a mixture of light of a lot of colors (called a spectrum, another subject). You can prove this with a prism, which separates the colors of what we normally call white light or sunlight. These various colors are actually just different sizes (wavelengths or frequencies) of waves of radiation (light). Our eyes only recognize the total of all this light, and so it appears to us to be a bright
Here is something interesting to think about: When you look at the nighttime sky, it’s black, with the stars and the moon forming points of light on that black background. So why is it that, during the day, the sky doesn’t remain black with the sun acting as another point of light? Why does the daytime sky turn a bright blue and the stars disappear? The first thing to recognize is that the sun is an extremely bright source of light — much brighter than the moon. The second thing to recognize is that the atoms of nitrogen and oxygen in the atmosphere have an effect on the sunlight that passes through them. There is a physical phenomenon called Rayleigh scattering that causes light to scatter when it passes through particles that have a diameter one-tenth that of the wavelength (color) of the light. Sunlight is made up of all different colors of light, but because of the elements in the atmospher
