How many light years away is the nearest star to the Sun?

How to get close to this number

The trick is to reason from the unit instead of from the distance. A light year is defined by how far light covers in a year, and you already know light crosses the Earth–Moon gap in about a second. So the question becomes: how many seconds are in a year, and how many of those trips fit into the answer? Framing it that way converts an unimaginable distance into ordinary arithmetic.

Most people guess too low, and the reason is that "nearest" reads as "close". It is nearest only in the sense that nothing else is closer; in absolute terms the gap between two neighbouring stars is vastly larger than the gap between the planets inside a single solar system. This is the number that quietly settles the question of interstellar travel, and it is why the trip time in the explanation above runs to thousands of years rather than decades.

Worth knowing what the figure describes: Proxima Centauri is a small, dim red dwarf, invisible to the naked eye, and it is gravitationally bound to the much brighter pair most people mean when they say Alpha Centauri. Its distance is known extremely precisely because it is measured by parallax — the tiny shift in a star's apparent position as the Earth moves from one side of its orbit to the other — which is geometry rather than inference, and space telescopes have made it sharper still.