“Sometimes a person has to go a very long distance out of his way to come back a short distance correctly.” –Edward Albee
Every week on Ask Ethan, we’ve been taking a look at my favorites of the questions you send in. And one of the things you’ve been wondering about is this: when we look at an object way out there in the Universe, how do we determine how far back in time we’re looking.
Is it as simple as measuring the distance to it and calculating the time by using the speed of light? If only. That might work for the nearest stars (and possibly a handful of the nearest galaxies), but that approach begins to break down fast the farther away we look for one simple reason: the Universe is expanding!
So what do we need to do in order to figure it out? Go read the whole thing and you’ll know, too!