Are the stars in the sky already dead?

It’s true that when we look up into the night sky we are not seeing a real-time version of the stars, but versions of them as they were in the past. The stars closest to Earth, in the Alpha Centauri triple-star system, are 4.37 light-years away, which means it takes four and a half years for their light to reach us. Should your gaze happen to alight on a star from that system, you’re seeing it as it looked four years ago. It may have died since then, in which case you are seeing light from a star that no longer exists. But that’s rare: on average, just one star goes supernova per galaxy per century so most of the stars you can with the naked eye are still very much alive. It’s only when you look much deeper into the galaxy using a telescope that you may end up looking at light in our night sky that has travelled from stars that are long gone.

Quick fact