Astronomy
What the Cosmic Distance Ladder Tells Us About the Universe's Scale
Quick fact
The cosmic distance ladder is not a single device but a series of overlapping methods, and if the first rung is slightly off, every more distant measurement shifts along with it—which is why measuring Cepheid variables with space telescopes caused major revisions in the scale of the universe.
Why this is interesting
When you look at a distant galaxy, how do you know how far away it really is? Astronomers cannot stretch a tape measure across space, so they built a ladder of indirect techniques that reaches from nearby stars to the edge of the observable universe.