Why is the sky blue?

Why is the sky blue?
Quite often I can’t sleep at night. In the early hours of the morning ridiculous questions engulf me. So, just why is the sky blue?

Since ancient times there have been many theories. A couple of them were bonkers, the others somewhat understandable. Some believed it was the reflection of the oceans. Others believed it was the blue cape belonging to the gods. Quite a few were convinced that the sky was full of valuable blue gemstones.
So here my simple explanation:
The sky is blue because of the way light interacts with our atmosphere.

As we know light is made up of several colours. It is just that the blue component get scattered more in our atmosphere than the other colours.

if the universe was slightly different we could have had a purple sky! I’m sure all of the Goths would have loved that.

The above then made me think about light and dark. The following popped into my head

If the universe is infinite then I should see a star in every direction. For instance why is the sky so black on the moon landing pictures? There doesn’t seem to be a single observable star in the background. I bet there’s a few of you now shouting that the moon landing was a fake! I think that is a discussion for another topic.

Feel free to post a reply if you have a comment on the above.
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