Telescopes as Time Machines

One of the weirder concepts in astronomy is that telescopes are like time machines. Light travels at a finite speed -- it's incredibly fast: 300,000 kilometers per second -- but finite nonetheless. It takes a second or so to light to get from the Moon to Earth, eight minutes to reach us from the Sun, and over four years from the nearest known star. When you start talking cosmic distances, those numbers reach into the billions of years. So when we use a telescope to look at some distant object, ...