Why is the Sky Blue?
Why is the sky blue? Why is the Earth hotter during summer than it is during winter? These are two basic science questions that many intelligent, educated people can’t answer.
The subject arose as part of a discussion in a science podcast related to the gap between the arts and science but I think it is equally applicable to the gap between people who are scientists, technologists, or just scientifically literate for some other reason, and everyone else.
According to the program, when the entire graduating class of Harvard University was asked why the Earth is hotter in summer only a few gave the right answer. Not only is does this show a huge failure to know some basic facts (this is usually taught in school at around age 13, I think) but the answer most people give makes no sense if you think about it a bit.
The most common answer is that the Earth is closer to the Sun during summer. This seems reasonable until you realise that during the northern summer the southern hemisphere has its winter. Since both hemispheres are part of the same planet how can one be closer and experience summer while the other is more distant and be experiencing winter?
If Harvard graduates (who most people would say are fairly intelligent) can’t even see this simple problem with their answer then what chance does everyone else have?
By the way, the correct answer is that its the direction of tilt of the Earth which changes. The Earth is tilted at about 23 degrees in relation to the Sun and the direction the Earth points stays the same as the Earth orbits the Sun.
So when the Earth is on one side of its orbit and the northern hemisphere is pointing more towards the Sun during December and January it is hotter but six months later on the other side of the orbit when it is pointing more away it is colder. Of course when the northern hemisphere is pointing away the southern is pointing towards the Sun (and vice versa) so its seasons are opposite. That’s not too hard, is it?
If people can’t even handle that concept then what chance do they have with more subtle and abstract ideas, like quantum physics, evolution, and cosmological theories? And what about complex and contentious ideas like global warming?
Does this all really matter though? Well yes, because people would be called ignorant if they didn’t know a few basic facts about literature (some lines from Shakespeare maybe) or some simple geography (the capital of major countries) or some history (approximate dates of the world wars) but most people don’t seem to worry as much about scientific ignorance even though it is of greater practical importance.
Actually, looking at the paragraph above I’m not so sure I’m right because I suspect a lot of people wouldn’t have any clues about those non-science questions either. In fact I seem to remember a survey which showed many people didn’t even know which century World War I was in! So maybe I shouldn’t re railing against scientific ignorance as much as pure, generic ignorance!
Oh yes, I haven’t told you why the sky is blue yet, have I? The molecules in air scatter shorter (bluer) wavelengths of light more than longer (redder) so they get diverted down from the sky to where we see them. The red stuff goes right through. At sunset the sky seems redder for the same reason: the blue is being diverted away and the red is coming through in a straight line.
But that explanation is really too complex. Exactly the same effect occurs in a tank of coloured liquid or gas and we don’t engage in complex explanations for that. So really the reason the sky is blue is simply because air is blue!