Old light

Light is the fastest thing there is, but space is big. Sunlight takes about eight minutes to reach us, so we see the Sun as it was eight minutes ago.

The nearest star beyond the Sun is about four light-years away: its light set out four years ago. Many of the stars you can see by eye are dozens to hundreds of light-years away.

So looking up is also looking back. The night sky is not one moment — every point of light left at a different time.