|
Why is the sky dark at night?夜空为什么是黑的？ You might think the answer is obvious - the sun isnt up! But the only reason the sky looks blue during the day is that sunlight scatters off of the atmosphere - if we didnt have an atmosphere (like on the moon), the sky would always be dark, even when the sun is shining. So lets rephrase the question - why is space dark?你可能认为答案很简单——因为没有太阳嘛！但白天的天空之所以是蓝色的，完全因为大气层把阳光散射了。而如果没有大气层，就比如月球，那么天空就一直都是黑的，即便有太阳照射，那就让我们换种问法——为什么太空是黑色的？ 太空里充满了各种各样的恒星，每一颗的亮度都和太阳一样，而在无穷无尽的宇宙中，不管你选择任何一个方向，只要你走得足够远，你都能遇到一颗恒星，或者一个星系，于是天空就应该是亮如白昼的，不论白天还是黑夜。And since its not, does the darkness of the night sky mean that theres some distance away from us when stars and galaxies just… stop? A boundary between something and nothing?但是事实却并非如此，那么，黑色的夜空是否告诉了我们，在一定的距离以外，就没有恒星或者星系了吗？是不是存在一个有星星和没有星星的边界？ | 
