As a child I thought that the question "why is the sky blue?" was unanswerable. As it turns out, this question is commonly answered using refraction in the atmosphere etc. However, if you now ask, "why is the night sky black?", the best answer you will get is Olber's paradox - it's black because it's not light. Therefore it seems that the real question of why the night sky is black is not answerable. So my question is, how do we know which questions can be answered and which are meaningless? It seems as though the question "why is the day sky blue" is answerable whereas "why is the night sky black" is unanswerable.