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Supernova clarification

Supernova clarification. Created by Sal Khan.

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Video transcript

I want to make one clarification on my video on supernovae, because that's the plural for supernova, is that I said this supernova occurred 1,000 years ago. That's actually not precisely right. The supernova was first observed 1,000 years ago, or the light from that first explosion was observed by astronomers we believe 1,000 years ago. But we have to be very clear here. Because the Crab nebula at its core is roughly 6,500 light years away, even this light, even this image we see right here is that nebula as it was 6,500 years ago. And so the supernova itself, if we think about when it actually occurred, it actually must have occurred about 7,500 years ago. So it must have occurred about 7,500 years ago. And that first slide from that first explosion from that first energetic event reached us about 1,000 years ago. So it took 6,500 years to get to us, and reached us 1,000 years ago. So first light 1,000 years ago. Just wanted to make that clear. Might have been obvious to some of you all, but always important to think about it. When I said 1,000 years ago, I really should have said it was first observed, the explosion was observed 1,000 years ago. But since it's so far, the actual event must have occurred 7,500 years ago.