What’s the Oldest Light You Can See Tonight?

“What do you mean?”

“Light has a speed too. No matter how fast it travels, it still takes time to reach us. So the farther away a star is, the older that light is by the time it finally arrives.”

“So the star I’m seeing right now is actually showing me what it looked like a long time ago?”

“Exactly right. For a nearby star, that might just be a few years ago. But for a star that’s really far away, it could be hundreds or even thousands of years ago.”

“So what’s the oldest thing we can see tonight?”

“Among things visible to the naked eye, the Andromeda Galaxy is probably the oldest. Its light took about 2.5 million years to reach us.”

“2.5 million years?”

“Yep. So if you look at the Andromeda Galaxy tonight, you’re seeing exactly what it looked like 2.5 million years ago. What it actually looks like right this second, nobody actually knows.”

“So could that star maybe not even exist anymore?”

“Theoretically, yes. Since starlight takes so long to arrive, some of the stars we see might have already disappeared. We could be looking at the very last light that star ever sent out.”

“That’s amazing but also kind of sad.”

“You could think of it that way, but you could also think of it like this. Every time you look up at the night sky, you’re actually traveling back in time. It’s like a gift the universe gives us.”