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Comment by ars | Hacker News Reader

We would see it years before, and we would know with certainty years before.

If the object really looked like it might impact I'm sure someone would get time on a powerful telescope to lock in the orbit.

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How far in advance would we know exactly _where_ on the Earth it will hit? If, say, New York is going to be destroyed, it makes a big difference if we know that a year in advance vs. a day.

Does it though? People don't leave hurricane zones. People don't heed tornado warnings. I just have very little faith in humanity, and fell like "Don't Look Up" would be not too far off.

Also, if you evacuate New York a year in advance, who's to say that the prediction isn't just a skosh off so that New York is left untouched but the real impact location was hit unprepared?

A lot of people do evacuate hurricane zones, even when death and destruction are not absolutely guaranteed. If we knew with certainty that a particular place was going to be hit by an asteroid, and we had time to evacuate, I am confident most people would do so.

The accuracy issue is the thing. I’d venture a guess that our prediction of the path of a hurricane 7 days out is more accurate than predicting where an impact will be.

It's actually the opposite. Calculating an asteroid impact is much easier because it primarily involves basic Newtonian physics. In contrast, the climate is a chaotic system, making long-term predictions far more complex.

I don't know how it's opposite. There's some complex guesstimating on where an asteroid will hit. We roughly know its size. We roughly know its composition. We roughly know its speed. We can give a +/- range where the impact area will be. That's not any different than how hurricane spaghetti models do.

The difference is knowing the size, speed and composition of a hurtling rock tells you where it's going to go, where as knowing the size, speed, and composition of a hurricane does not tell you where the hurricane will go. Complexity isn't a problem, the issue with weather prediction is that it's chaotic - extremely small changes to starting conditions cause large changes to the end result.

What was the compliance rate in evacuating parts of LA for the recent fires?

There's always a few holdovers, but my experience living in disaster prone areas is that people evacuate when evacuation orders are given. Literally nobody is going to come help you if you don't.

Having lived through a bunch of hurricanes in south Florida I can very confidently say people absolutely evacuate when given the order to.

Knowing if it will hit is a lot easier than knowing where.

Knowing where, will depend on the angle of impact - if came basically straight in (tangent to the surface) we can be pretty accurate, but the more shallow the angle the harder it will be.

With a shallow angle, we'll probably be able to tell the latitude pretty well, but not the longitude.

Nitpick: normal to the surface.

Oops! Yes, I meant to say perpendicular (or normal).

It must be easy to determine which face of the earth it strikes though...?

The earth rotates on its axis, So knowing the exact point it hits would depend on the exact time it hits. Presumably that's why the other commenter said knowing latitude would be easier than knowing longitude.

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