🔭 Light and distance

A light-year is not a measure of time but of distance, the enormous distance that light travels in one whole year. Light is the fastest thing there is, so a light-year is a truly huge stretch of space. We use it because the distances between stars are far too big to measure in kilometres.

Yes, in a way it is. Starlight takes a long time to reach us, so when you look at a distant star you see light that left it years, or even thousands of years, ago. You are seeing the star as it was in the past, not as it is right now. The farther away it is, the further back in time you look.

Not counting our own Sun, the closest star is so far that its light takes more than four years to reach us. Even in the fastest spacecraft we have built, the trip would take tens of thousands of years. Space is mostly vast, empty distance between very far-apart stars.

Yes. Scientists have discovered that the whole universe is slowly stretching, and galaxies are drifting farther and farther apart. It is not that they fly through space away from us, but that the space between them keeps growing, like dots on a balloon spreading apart as it inflates.