The sunlight on a windowsill is about eight minutes old, which is the part everyone knows. The rest of its journey took far longer. Energy made in the Sun’s core can’t travel straight out: through most of the interior the gas is so dense that light is absorbed and given off again after a tiny step, in a random direction, over and over, so it staggers outward like someone lost in a crowd. Estimates of how long that walk takes run from about ten thousand years to well over a hundred thousand. Near the top, boiling gas carries the energy the rest of the way, and at the surface the light finally goes free and crosses the 150 million kilometres to us in about the time it takes to hard-boil an egg. Almost all of the trip happens where nobody can see it. The eight minutes is just the doorstep.