If you want to see the universe as it was, say, a thousand years ago, or 10,000, or more, it can be done, provided you have a way of capturing light from a distant place. That’s because it travels at a finite speed, about 300,000 km a second, and the universe is large enough that it can be measured in light years, the distance light travels in one year, at 300,000 km a second. A light year is about 9.46 trillion km. The observable universe—the part we can see and study—is about