This is the fourth post in as many as possible in this series.

I reached out to a few people and asked for suggestions for topics to write posts in this theme on.
I’ve been keeping these in my drafts for a while now. I intend to publish them over this month. The simplest one I got, that I decided to start with, was a question I learned to answer a long time ago while in school, but, had to revisit to relearn.

I’m also considering moving this series over into a different format, with actual discussions instead, more on that later.

“Why is sky blue?”

To understand why the sky is blue, we must understand what the sky consists of and what light really is.
While there is a lot of empty space out there, the atmosphere is significantly denser than space that exists outside of the atmosphere.
This means that there are a lot of particles out that are colliding with each other and can scatter anything else that it hits.

Light exists, for the purposes of this discussion, as a wave. Every colour has a wavelength associated with it. If you tied a string to 2 pins and plucked it up in any part of the string, you would create a wave. If you look at how it vibrates, you’ll see that there are distinct repeating points where the string reaches the highest point. The distance between any 2 of this distinct points is the wavelength of the wave.

As I mentioned earlier, every colour has a wavelength associated with it. It vibrates in this way creating wave, which actually define what colour we see.

The sun emits white light, which comprises of all visible colours and when white light hits any of the particles in the atmosphere, it scatters.

How much each colour in the white light is scattered by is determined by its wavelength. It’s actually inversely proportional to the wavelength of the wave, which means that the shorter the wavelength, the more it is scattered, the longer, the lesser it is scattered.

There are 7 distinct colours in white light, best remembered as the colours of the rainbow, and red has the longest wavelength, while blue has the shortest.
As a result, blue gets scattered a whole lot more than red, which makes it more predominant in the sky above.

This is why, sky, in general, is blue.


This I thought was a reasonably simple explanation, I didn’t actually try this one out with anyone, so, I’m not sure how simple it is.

Would love to hear any comments/criticism/feedback/further questions, I’m just trying to improve here.

Thank you for reading
Sainath