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Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

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Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#41

Post by iSnow »

gnosis wrote: post #25
Shank wrote: post #7

Earlier quoted context omitted.

This is slightly true, though notably the Torino Scale mentions that once an object is classed at level 5, governments may begin to take action to counteract such a collision before it arrives at earth, if the encounter is set to be less than a decade away. http://en.wikipedia.org/wiki/Torino_Scale Edit: NASA's JPL maintains the Sentry Risk Table, which tracks all objects that may impact the Earth, with various data…

The time to initiate an asteroid defense project is long before a threat is even detected. There needs to be time for technology development, deployment, and testing. Tackling an extinction-level event is not something we want to scramble for at the last possible minute, using untried technology.

> Tackling an extinction-level event is not something we want to scramble for at the last possible minute

I am not sure if this is in line with Agile principles like YAGNI.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#43

Post by shasta »

ars wrote: post #30
danso wrote: post #27

Earlier quoted context omitted.

I had never heard that saying before but I fear I will use it much too often in the future

It's from this: http://en.wikipedia.org/wiki/Zebra_%28medicine%29

From the second sentence of your link: The term derives from the aphorism 'When you hear hoofbeats behind you, don't expect to see a zebra'.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#44

Post by Gravityloss »

ars wrote: post #30
danso wrote: post #27

Earlier quoted context omitted.

I had never heard that saying before but I fear I will use it much too often in the future

It's from this: http://en.wikipedia.org/wiki/Zebra_%28medicine%29

This would call for a primer in Bayesian inference. Actually, all medical practice would benefit from understanding it.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#45

Post by wedesoft »

bad_user wrote: post #39
gnosis wrote: post #25

Earlier quoted context omitted.

The time to initiate an asteroid defense project is long before a threat is even detected. There needs to be time for technology development, deployment, and testing. Tackling an extinction-level event is not something we want to scramble for at the last possible minute, using untried technology.

Research in this area should have happened since yesterday, but deployment and testing? The probability of something big hitting us is really low, coupled with the fact that we can see it coming since all objects in space are visible. Miss-calculating a trajectory could indeed happen and we may not notice it if it's coming from the direction of our sun, but the probability of that is even lower. So why would you spen…

> since all objects in space are visible

The majority of objects in space are not visible to us. They only become visible when near and bright enough. Even known comets such as Halley are not visible to us most of the time.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#46

Post by bad_user »

wedesoft wrote: post #45
bad_user wrote: post #39

Earlier quoted context omitted.

Research in this area should have happened since yesterday, but deployment and testing? The probability of something big hitting us is really low, coupled with the fact that we can see it coming since all objects in space are visible. Miss-calculating a trajectory could indeed happen and we may not notice it if it's coming from the direction of our sun, but the probability of that is even lower. So why would you spen…

> since all objects in space are visible The majority of objects in space are not visible to us. They only become visible when near and bright enough. Even known comets such as Halley are not visible to us most of the time.

Not with the naked eye as the sunlight reflected by Earth makes that difficult, but we do have deep space telescopes, don't we?

I don't know much on this topic, but if we are able to spot planets that are light years away, then what's the problem with detecting objects that are gonna crash into us in the next 1000 years?

The only problem I can understand is that the sky is a pretty big place, but surely we also have a lot of time to detect such objects.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#47

Post by quarterto »

mistercow wrote: post #11
temphn wrote: post #6

No photographic evidence. No corresponding accounts. No raw data. Bonilla published his account of this event in a French journal called L'Astronomie in 1886. Unable to account for the phenomenon, the editor of the journal suggested, rather incredulously, that it must have been caused by birds, insects or dust passing front of the Bonilla's telescope. As the saying goes: when you hear hoof-steps, think horses, not ze…

Yeah the prior probability of "fragmenting comet within 8000 km of Earth" seems kind of a lot lower than that of "dust in front of the telescope".

http://rationalwiki.org/wiki/Improbable_things_happen

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#48

Post by mistercow »

quarterto wrote: post #47
mistercow wrote: post #11

Earlier quoted context omitted.

Yeah the prior probability of "fragmenting comet within 8000 km of Earth" seems kind of a lot lower than that of "dust in front of the telescope".

http://rationalwiki.org/wiki/Improbable_things_happen

That's a silly argument. Yes, improbable things happen, but our beliefs should be informed by whatever hypothesis is assigned the highest probability.

The difficulty that a hypothesis with very low prior probability (like this one) has is that in order for it to reach a level of probability necessary to compete with the more mundane explanations like dust or birds, it is going to have to be backed by very strong evidence. This is the Bayesian expression of "extraordinary claims require extraordinary evidence". The hypothesis needs to make some predictions that are exceptionally unlikely given those mundane hypotheses.

Unfortunately, it's difficult to see what predictions those might be. The authors of the paper don't give any, and their primary "evidence" for the hypothesis - that nobody else saw the object - is actually more likely given the birds/dust hypothesis than the comet hypothesis.

So yes, there's a tiny possibility that this could have been a comet, but if so, it's hard so imagine that it could ever be elevated to the point of a hypothesis that we should even take seriously, much less one that we should believe.

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#49

Post by peeters »

bad_user wrote: post #46
wedesoft wrote: post #45

Earlier quoted context omitted.

> since all objects in space are visible The majority of objects in space are not visible to us. They only become visible when near and bright enough. Even known comets such as Halley are not visible to us most of the time.

Not with the naked eye as the sunlight reflected by Earth makes that difficult, but we do have deep space telescopes, don't we? I don't know much on this topic, but if we are able to spot planets that are light years away, then what's the problem with detecting objects that are gonna crash into us in the next 1000 years? The only problem I can understand is that the sky is a pretty big place, but surely we also have…

Planets outside of the solar system are not detected using light from the body itself. They are detected by their gravitational pull on their host star (i.e. tides; causing a slight twinkle in the light emitted by the star), or a transit (eclipse) of the star (causing the star to become slightly dim for a period). In both cases the telescope is looking at stars, and isn't fixated on one star but rather a field of stars, waiting for one to show activity.

Never mind the fact that even if we have a telescope that big, the issue is that these telescopes show a microscopically small field of view. There's a whole sphere that would need to be observed, and repeatedly (since the bodies move).

Re: Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883

#50

Post by ajuc »

bad_user wrote: post #46
wedesoft wrote: post #45

Earlier quoted context omitted.

> since all objects in space are visible The majority of objects in space are not visible to us. They only become visible when near and bright enough. Even known comets such as Halley are not visible to us most of the time.

Not with the naked eye as the sunlight reflected by Earth makes that difficult, but we do have deep space telescopes, don't we? I don't know much on this topic, but if we are able to spot planets that are light years away, then what's the problem with detecting objects that are gonna crash into us in the next 1000 years? The only problem I can understand is that the sky is a pretty big place, but surely we also have…

We detect these planets light years away when they go between us and some light source, or when they change orbit of some light source (thanks to gravity). If the body is cold and the background is black we won't see it until it's close to our sun.
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