When you look at a star, are you seeing the past?

Step outside at night, look up, and take this in: nothing you see is happening “now.”

Light is blazingly fast — 299,792 km per second — but not instant. It takes time. The Sun’s reaches you with an 8-minute, 20-second delay: if it went out right now, you’d see it shine for 8 more minutes. The nearest star, Proxima Centauri, is 4.24 light-years away: you see it as it was more than four years ago.

And the distant ones? When you look at Polaris, the North Star, you’re seeing light that left around 1590 — before Shakespeare wrote Hamlet. Some stars you can see with the naked eye have been dead for thousands of years; their light is still traveling to your eyes.

Every night, quite literally, you’re looking at ghosts. The sky isn’t a photo of the present: it’s a time machine switched on above your head.