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I've read a lot of questions about the specifics of meteor impacts on this site, but strangely this one seems to still elude me:

Assume a meteor of sufficient mass and speed to wipe out human life within a week (if not sooner) impacts the planet. What does this look like from the perspective of a person on the ground? No real change until instantaneous vaporization? Death by a massive shockwave? Localized devastation followed by a slow collapse to environmental causes?

To be specific: from the moment the meteor is seen by the naked eye to the extinction of life on the surface, and from the perspective of a human observer, what happens in what order?

The impact in question happens over land, and at a roughly perpendicular angle; the observer is able to see the impact site at the edge of the horizon assuming they're elevated no more than a storey above flat terrain.

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    $\begingroup$ Do you mean literally look like, as in being observed exclusively visually? Or do you mean more generally what the experience would be like? It would seem to be pretty difficult to, standing on local ground, see something that happens on the other side of the planet... $\endgroup$ – a CVn Jan 24 at 19:22
  • $\begingroup$ Welcome to Worldbuilding, Naota! If you have a moment, please take the tour and visit the help center to learn more about the site. You may also find Worldbuilding Meta and The Sandbox useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. Have fun! $\endgroup$ – Gryphon Jan 24 at 19:27
  • $\begingroup$ The Walking With Dinosaurs book contains a rather lengthy description of the devastation caused by the meteor impact that wiped out the dinosaurs, but I don't know a) how scientifically accurate it is, and b) whether it fits your definition of "world-ending". $\endgroup$ – F1Krazy Jan 24 at 19:28
  • $\begingroup$ Wiping out ALL humans within a week it tough. The asteroid has to be a lot bigger than Chicxulub impactor $\endgroup$ – Alexander Jan 24 at 19:34
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    $\begingroup$ A bright light, a rushing wind, a brief moment of pain... and then oblivion. $\endgroup$ – Arkenstein XII Jan 24 at 21:15
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If you are close enough to see it visually, and you're not in some kind of bunker, you'll die before the information from your eyes reaches your brain. The infrared and visual light from the impact will cook you instantly. You might actually even die before the impact, the asteroid itself will be heated to such an extreme degree it may cook you as it flies overhead.

If you ARE in a bunker, you'll see a blindingly bright flash. Once it dims enough to open your eyes, you will see a huge, white sphere expanding from the impact site at a few times the speed of sound; this is water vapor, condensed out of the air by the shock wave. If you and your bunker survive the shock wave, you'll see a towering fireball at the impact site, with more meteors streaking away from it; these are rocks from Earth blasted away at hypersonic speeds. Some of these will fall back to the Earth and cause their own impact events.

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  • $\begingroup$ The impactor is unlikely to move at such speed so that it could not be seen before it kills the observer. $\endgroup$ – Alexander Jan 24 at 21:34
  • $\begingroup$ Faster than the speed of light? Feels kind of fast. It was thrilling to read this answer, though. $\endgroup$ – Isaac Jan 24 at 21:46
  • $\begingroup$ This is pretty much how I would have answered it. If you are within the horizon distance and therefore close enough to see the impact itself, you will be killed almost instantly. $\endgroup$ – Arkenstein XII Jan 24 at 21:53
  • $\begingroup$ @Alexander If the impactor comes in from the far side of the impact site, it never actually flies over you before it hits the ground. Imagine if it flies in from beyond the horizon, and hits at the horizon. It wouldn't cook you then. $\endgroup$ – Ryan_L Jan 24 at 22:09
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    $\begingroup$ @Isaac information does not travel from your eyes to your brain at light speed. $\endgroup$ – Harabeck Jan 24 at 22:15

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