There isn’t one edge — there are three, and they are startlingly far apart. Distances below are shown as everyday journeys at your chosen Sun size, because the real model numbers get too big to picture.
But how does anyone know these distances?
Nobody has ever stretched a tape measure to a star. Instead astronomers use a ladder: each method is calibrated by the one below it, and each reaches further than the last. Tap a rung.
⚠️ Why it matters that it’s a ladder: an error on a low rung propagates all the way up. Sharpening the bottom rungs — especially parallax — is exactly what the Gaia spacecraft was built for, and it is central to today’s unresolved “Hubble tension”: the expansion rate measured up the ladder disagrees with the rate predicted from the early universe by about 8%.
Sizes and mean orbital distances are real astronomical values scaled uniformly. Distances use each planet's average distance from the Sun (orbits are ellipses, so the real distance varies). Computed on your device. About & credits ·