The Astronomy Thread

Eomer

Eomer

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Jive Turkey_sl said:
Even if we had the means to deal with something that size, just seeing it coming before it's too late is another thing all together.
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And if we do see it well in advance, with present technology it's probably easier and more effective to evacuate the city that is going to get hit than it would be to try to mount some sort of last second interception/deflection mission.
 
Ukerric

Ukerric

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Eomer_sl said:
And if we do see it well in advance
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You are probably over-estimating our capacity to pinpoint the impact.

Quick math: an impactor at 20km/s, 1 day away is somewhat 1 million miles away, 5 times the earth-moon distance. You're probably going to determine in which country/state it's going to hit, but which city is not going to be guaranteed if it's populated. By the time you can accurately guess which city is most at risk, you're mere hours away, and there's no way to evacuate a modern city in hours. So do you evacuate all of them in range? That escalates the costs quickly.

An example: You determine an impactor set for the east coast, and it looks like it's going to hit Virginia in about 1 day and Richmond is at risk. If it hits 20mn earlier, it's blasting Cheasapeake, if its 20mn later than you guessed, it's Charlottesville who bites it. Or anything inbetween.
 
iannis

iannis

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The technology to be able to even do that much would serve us more practically and more consistently in other ways. That's what strikes me as unreasoned panic about the thing. Not that it's a waste of time to pursue precise stellar cartography, but that doing it because "an asteroid might hit us" strikes me as a generally kinda dumb reason.

I don't mean it's something we shouldn't do. It seems like something we have to do if we ever expect intra-stellar traffic.
 
Eomer

Eomer

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I was under the impression that astronomers would be able to give a pretty decent estimate of the impact zone a few days ahead of time with current technology. I guess I was mistaken?
 
Alex

Alex

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Yeah you'd think we could do that given our insane ability to sling shot satellites from other planets and comets and shit.
 
Szlia

Szlia

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My first guess is that you can't tell easily how... cohesive the asteroid is. By that I mean that it's tough to tell if it will not lose some chunks because of gravitational forces, making the trajectory difficult to estimate. And then there is atmospheric entry and bets are off as to what happens to the asteroid and its trajectory then.
 
iannis

iannis

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Well lets see, you have to find them first. Currently most of our detection methods are light based, and asteroids are tiny and dark. Even huge ones. So there's a hurdle. After you find it you have to take readings on which way it's going and how fast it's going. That takes being able to reliably find it again, a little bit of time, and a little bit of math. And then you would have the geology of it if you're talking about pinpointing impact sites.

It seems like the first two we're pretty close to being able to do if we invested some time into it. It seems like the third one would require a significant investment of social capitol. We had that probe land on the comet recently, and that's cool. But you'd have to be throwing probes at random chunks of rock which you identify to be on a possible collision course and you'd have to be able to mount it quickly. Or else you'd have to devise a way to do that sort of detailed analysis at great ranges. Which I'm sure you could do, but it would probably require a network of satellite telescopes orbiting in the system.

I mean maybe there are planetbound ways to do it and i'm just ignorant. But I mean... lets start tossing up a blanket of telescopes in the star system just to do it, not cause we're a little concerned about Apophis.
 
Palum

Palum

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All that is basically worthless if the composition makes it unstable but still solid enough to not fully disintegrate on entry - there's no way to know exactly where/when the atmospheric drag will cause it to fragment and where they will go.
 
Dandain

Dandain

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Precisely where it will hit to the meter is not necessary to know, the math will still provide a region and a best/worst case for debris field as impact approached. One other thing to consider in regards to intercepting such a body is that not every direction and location from Earth is equivalently easy to reach with current technology since traveling in a straight line is remarkably hard to do with any speed. Any object on collision with Earth may require years in advance detection to allow current technology intercepts as it might take years or a very specific launch window.
 
Moogalak

Moogalak

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could that signal be a fast radio burst (frb) like the ones that were recently observed from two black holes merging?
 
Moogalak

Moogalak

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Might be right, but there just isnt enough data to say either way; from the wiki:

Ehman has voiced doubts that the signal was of intelligent extraterrestrial origin: "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris."[16] He later recanted his skepticism somewhat, after further research showed an Earth-borne signal to be very unlikely, given the requirements of a space-borne reflector being bound to certain unrealistic requirements to sufficiently explain the signal.[17] Also, it is problematic to propose that the 1420 MHz signal originated from Earth since this is within the "protected spectrum": a bandwidth reserved for astronomical purposes in which terrestrial transmitters are forbidden to transmit.[18][19] In a 1997 paper, "The Big Ear Wow! Signal: What We Know and Don't Know About It After 20 Years", Ehman resists "drawing vast conclusions from half-vast data"-acknowledging the possibility that the source may have been military or otherwise a product of Earth-bound humans.[20]
 
U

UnobservantBastard_sl

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Cad_sl said:
The HST's mirror is 2.4m, so how is a 2m space telescope 40 years later going to do anything? Where does the 300 times greater FOV come from?

JWST is like 6.5m and launches in 1.5 years.
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FOV is a function of focal length, not primary mirror diameter. Mirror diameter directly affects sensitivity, bigger mirrors gather more light. Coupled with larger focal plane sensors you can get better spatial resolution with a larger mirror, but the FOV will still be set by the focal length.

Relate it to standard DSLR camera lenses. A bigger mirror is analogous to a bigger lens, faster F-stop, finer depth of field. Nothing to do really with FOV, which is set by focal length. 10mm is a short focal length associated with wide FOV. 100+mm is telephoto, narrow FOV.
 
Cad

Cad

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ObservantBastard_sl said:
FOV is a function of focal length, not primary mirror diameter. Mirror diameter directly affects sensitivity, bigger mirrors gather more light. Coupled with larger focal plane sensors you can get better spatial resolution with a larger mirror, but the FOV will still be set by the focal length.

Relate it to standard DSLR camera lenses. A bigger mirror is analogous to a bigger lens, faster F-stop, finer depth of field. Nothing to do really with FOV, which is set by focal length. 10mm is a short focal length associated with wide FOV. 100+mm is telephoto, narrow FOV.
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Wouldn't you want a narrow FOV for a space telescope thats supposed to observe far-away things?
 
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