Why Is The Sky Blue?


To understand why the sky is blue, we first have to understand the composition of the the atmosphere. The atmosphere is mostly made up of nitrogen gas (78%), oxygen gas (21%) and small amounts of many other gases. In addition to the gases, the atmosphere has dust particles, pollen from flowers, evaporated salt from the oceans, and ashes and soot from incompletely burned organic matter. Near the ocean or after a rainstorm there may be more particles of water in the air. Pollution can add a variety of gasses, dust and soot to the atmosphere as well.

Now that we understand what our atmosphere is made up of, we have to take a better look at light particles (pun!). Light particles, or photons, are particles that travel in motions of waves. These light waves are vibrating electric and magnetic fields. Visible light is only a small part of what we call the electromagnetic spectrum. We classify light based on three characteristics: Wavelength, Amplitude, and Frequency. Wavelength is the distance between the tops (crests) of waves. Frequency is the number of waves that pass by each second. And Amplitude is the height of the waves.

When light travels through space, it travels in a straight line. As light enters Earth’s atmosphere, it comes into contact with dust particles and gas molecules and other components of the atmosphere that we discussed earlier. Dust particles and water droplets are much larger than the wavelength of visible light so when light hits these, it is either reflected and bounces off or refracted and breaks up into the many colors of the visible light spectrum (Rainbow!!). Gas molecules, unlike water droplets and dust, are much smaller and behave differently when photons hit them. When light hits a gas molecule, some of the light will be absorbed by the molecule. The light that is absorbed most frequently is the higher frequency blues, more so than the lower frequency reds. After some time, the gas molecule radiates (releases) the same light that it absorbed (most likely the higher frequency blue). The absorbed blue light is radiated in all different directions in the sky. Most of this blue light reaches us here on the land and as a result we see the sky as blue. 


After taking basic chemistry courses, I can say that the theory that light being radiated by gas molecules is possible because as a photon hits a gas molecule, it excites the electrons in the outermost layer of its electron cloud and the electron is kicked up an energy level. As we all know, the universe is trying to achieve minimum energy to become more stable. As a result, the electron in its excited state falls back down to it normal shell, and releases energy in the form of light. Which is what we see.


The sky is blue because it makes us all feel better about ourselves. The blue color of the sky gives me a warm fuzzy feeling every time I look at it. It makes me feel better about my day and it makes me feel like I’m in a warm place. When the sky is not blue, I get emotional and sometimes I cry.

What do you guys think? Do you like this? How about a question you would like me to answer for next weeks blog.

Sources Used-





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