A light-year is a distance, so why does it sound like a time?
When did that light leave?
Board 1 · Pick one and drag it to the telescope
From the shelf below, drag the Moon or any star and drop it in the night sky. Its light flies to the child's telescope.
Drop it anywhere here
Board 2 · The other way round — where is the light that left that year?
Drag the lantern along the road below, back into the past. If light that set out in that year is only now reaching our eyes, how far away did it come from?
The story behind this board
It reads far more easily after you have tried it.
To look at a star is to look at the past
Light-year
Telescope
Rømer — does light take time to arrive?
To the astronomy library →
The further away, the older the light. So to look at the very distant universe is to look at the very old universe. That is why a bigger telescope sees further back in time. Everything we see is a little in the past. Even the things in this room are a very short past.