|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On Wed, 02 Nov 2011 06:11:13 -0500, "U-m757\\bud"
wrote: The asteroid is supposed to be about magnitude 11.5, making it barely visible in small teelscopes. There's a finder chart in the November, 2011, issue of Sky and Telescope. Closest approach is about sunset in the mid-US. I think the only interesting part is that the asteroid is moving fast enough for motion to be visible if you can manage to find it. Tricky visually, but trivial with the smallest of scopes and the most basic of imaging equipment. |
#12
|
|||
|
|||
asteroid close approach, 2011 Nov 08
For the sake of general interest: Can we examine Brad's "lunar
glancing impacts" in greater depth? How does an airless body, like the Moon, affect impacting bodies? I presume the final angle of impact (on a theoretically smooth lunar surface) would be mass/velocity/approach angle dependent? Despite a preponderance of round craters, of all sizes, there do seem to be signs of lunar chain craters. Suggesting a bouncing/glancing trajectory of a "smallish" object travelling at high enough velocity (or having enough momentum) to cause a Dambuster's "skipping" effect. Hardly a "glancing off" since they never escaped the Moon's gravity again. How large and/or fast does a B.R.A.D (Big Rogue Alien Destroyer) have to be, in reality, to achieve a true "glancing impact" on the Moon? In best Hollywood, bone crunching style! Perhaps it's not such a simple question? |
#13
|
|||
|
|||
asteroid close approach, 2011 Nov 08
Chris.B wrote:
For the sake of general interest: Can we examine Brad's "lunar glancing impacts" in greater depth? How does an airless body, like the Moon, affect impacting bodies? I presume the final angle of impact (on a theoretically smooth lunar surface) would be mass/velocity/approach angle dependent? Despite a preponderance of round craters, of all sizes, there do seem to be signs of lunar chain craters. Suggesting a bouncing/glancing trajectory of a "smallish" object travelling at high enough velocity (or having enough momentum) to cause a Dambuster's "skipping" effect. Hardly a "glancing off" since they never escaped the Moon's gravity again. How large and/or fast does a B.R.A.D (Big Rogue Alien Destroyer) have to be, in reality, to achieve a true "glancing impact" on the Moon? In best Hollywood, bone crunching style! Perhaps it's not such a simple question? Think celestial mechanics. The impactor is coming in on a hyperbolic trajectory. If the distance from the focus of the hyperbola to the vertex -- from the center of the body to periapsis -- is less than the body's radius, you've got impact. More and you've got a close flyby. In order to have a grazing impact, the trajectory can't go very far beneath the surface. It's a low probability event, but it does happen. It's instructive to use the same "B plane" approach that JPL navigators use for spacecraft. Set up a plane perpendicular to the incoming asymptote of the hyperbola, and examine the point in this plane where the asymptote -- not the trajectory itself -- intersects the plane. Given the mass of the body and the incoming velocity ("V-infinity"), you can determine what the miss distance must be in the B-plane in order to have a grazing impact. Think of the B plane as a dartboard: you have to hit a fairly narrow ring. It will turn out that *lower* velocities will have a higher chance of a grazing impact, because the trajectory is bent more. The above is pretty much independent of the size of the impactor, at least until it gets well beyond "dinosaur killer" size. I also seem to recall that craters appear circular until the angle of incidence gets to be quite large, on the order of 70(?) degrees from vertical. Chains of craters can be explained by binary objects. You're not going to get a "skipping" effect like a stone on a lake -- you'll get a splash with secondary craters. -- Bill Owen |
#14
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On Wed, 2 Nov 2011 13:11:08 -0700 (PDT), "Chris.B"
wrote: For the sake of general interest: Can we examine Brad's "lunar glancing impacts" in greater depth? How does an airless body, like the Moon, affect impacting bodies? I presume the final angle of impact (on a theoretically smooth lunar surface) would be mass/velocity/approach angle dependent? A body which strikes the Moon is typically in an elliptical orbit around the Sun. In the case of the Moon, which is essentially a binary planet with the Earth, a body passing within the system undergoes some perturbation, which tweaks (possibly substantially) the original orbit. Depending on the velocity of the object with respect to the Moon (which is largely determined by the eccentricity of its orbit), it may actually be captured by the Moon, in which case it will enter an approximately hyperbolic orbit with respect to the Moon, or it may simply crash at something above the lunar escape velocity. In any case, the effect of the Moon's gravity is to somewhat focus bodies into collisions- in other words, the Moon appears to have a larger collisional cross section than its actual size. But not by a lot. Despite a preponderance of round craters, of all sizes, there do seem to be signs of lunar chain craters. Suggesting a bouncing/glancing trajectory of a "smallish" object travelling at high enough velocity (or having enough momentum) to cause a Dambuster's "skipping" effect. A few percent of impacts are at low angles- under 15° or so, which can create oval craters or crater chains. Crater chains are not caused by skipping, however. They are caused by secondary debris, or by multiple impacts as the parent breaks up before the impact (like Hale-Bopp). Hardly a "glancing off" since they never escaped the Moon's gravity again. How large and/or fast does a B.R.A.D (Big Rogue Alien Destroyer) have to be, in reality, to achieve a true "glancing impact" on the Moon? In best Hollywood, bone crunching style! Perhaps it's not such a simple question? Any body which enters at greater than the lunar escape velocity could theoretically touch the surface and then continue out into space again- it doesn't matter whether it's a marble or an asteroid. But in reality, I think a non-glancing impact is likely to eject more material from the lunar surface. That's probably the mechanism that explains lunar meteorites on Earth. However, there's nothing to suggest that anything from the Moon has ever hit the surface of the Earth with hypersonic velocity. Stuff knocked off the surface of the Moon is likely to be too small to survive to the ground as anything other than ordinary meteorites- that is, harmless, non-cratering events of interest mainly to people who like owning expensive rocks. |
#15
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On Nov 2, 8:15*am, Chris L Peterson wrote:
On Wed, 2 Nov 2011 06:25:29 -0700 (PDT), Brad Guth wrote: No, it wouldn't. No debris would be large enough to reach the Earth's surface. At most, we'd see a meteor shower, and it wouldn't be dense enough to be much of a *threat to our satellites. You have such a simulator? Yes. Such impacts are modeled with a variety of simulation tools. In this case, however, you can get a pretty good estimate of the likely issues simply by looking at energy- which is not very large. But your simulator can't be public accessed or much less tweaked? If this 400 meter sphere of potential doom is made of fluff (less than 2 g/cm3), you could be right. If the asteroid is mostly metallic and pushing 8+ g/cm3 would put a whole other interpretation to this one. Do you know what it's made of? Are you saying that glancing blows do not happen? No, although they are very rare. Any contact of similar or greater mass at 13+ km/sec would yield enough impact secondary shard exit velocity to escape the moon, and thousand tonne shards of paramagnetic basalt are going to be problematic. No, they are not (and what does "paramagnetic" have to do with anything?) If you're so interested in simulation, where's yours? How do you think that a lunar collision with a mere 400 meter asteroid is going to produce a flurry of Earth-directed, non-frangible debris with individual diameters greater than 10-20 meters, which would be the minimum requirement for reaching the ground with high velocity? You really don't have any idea at all what you are talking about. And again, you haven't addressed the FACT that there is zero possibility of this body striking the Moon at all. 3.5+ g/cm3 = paramagnetic basalt. (1 m3 = 3.5 tonnes) Again and again, you keep taking credit for the miss. This means you also get the blame and responsibility for future hits. How's your personal liability insurance coverage for having caused global trauma? (got 100 trillion worth of insurance coverage?) Your interpretation of zero-risk from any impact of 264e6 tonnes at 13 km/sec is noted. Perhaps the worse case for Earth is a 1000 m3 solid of fused paramagnetic basalt that'll eventually find its way to Earth, not to mention a glancing blow whereas the asteroid lives on to return another day. If a 400 meter asteroid can get so close, then what's stopping a 4 km version from doing the same or worse by actually making contact with either our moon or Earth? Do you have a plan? http://translate.google.com/# Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet” |
#16
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On Wed, 2 Nov 2011 16:48:05 -0700 (PDT), Brad Guth
wrote: But your simulator can't be public accessed or much less tweaked? Can yours? If this 400 meter sphere of potential doom is made of fluff (less than 2 g/cm3), you could be right. If the asteroid is mostly metallic and pushing 8+ g/cm3 would put a whole other interpretation to this one. Do you know what it's made of? It doesn't matter what it's made of. The collisional dynamics are almost identical for stone or for iron. The KE released is determined by mass, not density. The energy released is orders of magnitude greater than the material strength of either stone or iron. Again and again, you keep taking credit for the miss. Credit? I'm simply pointing out that the trajectory is known, and it WILL absolutely miss. There's no credit to take. It's simple observation and simple physics. Bodies don't miraculously change direction. If a 400 meter asteroid can get so close, then what's stopping a 4 km version from doing the same or worse by actually making contact with either our moon or Earth? Absolutely nothing. Fortunately, the size of asteroidal and cometary bodies is described by a power law, and we therefore know that large collisions are rare. But they happen. Perhaps by the time the next one might occur, we'll have the technology to stop it. Or not. Do you have a plan? I've got more realistic worries to concern myself with. It's been millions of years since the last asteroidal collision large enough to have global effects, and is likely to be millions of years before the next. There's a very good chance there will be no humans on Earth when it happens. |
#17
|
|||
|
|||
asteroid close approach, 2011 Nov 08
That's about the Moon's orbit, so not very close.
|
#18
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On Nov 2, 4:57*pm, Chris L Peterson wrote:
On Wed, 2 Nov 2011 16:48:05 -0700 (PDT), Brad Guth wrote: But your simulator can't be public accessed or much less tweaked? Can yours? If this 400 meter sphere of potential doom is made of fluff (less than 2 g/cm3), you could be right. *If the asteroid is mostly metallic and pushing 8+ g/cm3 would put a whole other interpretation to this one. Do you know what it's made of? It doesn't matter what it's made of. The collisional dynamics are almost identical for stone or for iron. The KE released is determined by mass, not density. The energy released is orders of magnitude greater than the material strength of either stone or iron. Again and again, you keep taking credit for the miss. Credit? I'm simply pointing out that the trajectory is known, and it WILL absolutely miss. There's no credit to take. It's simple observation and simple physics. Bodies don't miraculously change direction. If a 400 meter asteroid can get so close, then what's stopping a 4 km version from doing the same or worse by actually making contact with either our moon or Earth? Absolutely nothing. Fortunately, the size of asteroidal and cometary bodies is described by a power law, and we therefore know that large collisions are rare. But they happen. Perhaps by the time the next one might occur, we'll have the technology to stop it. Or not. Do you have a plan? I've got more realistic worries to concern myself with. It's been millions of years since the last asteroidal collision large enough to have global effects, and is likely to be millions of years before the next. There's a very good chance there will be no humans on Earth when it happens. Your denial of being in denial is noted. That's kind of the same excuse GW Bush, Dick Cheney as well as our FBI/NSA/CIA/MI6/Pentagon and DoD each had to say about OBL prior to 9/11, essentially informing us by way of their obfuscation that we had nothing to worry about.. Your orbital simulator that can't be shown nor demonstrated in public must be a really good one if it takes multiple 3-body variables into account. http://translate.google.com/# Brad Guth, Brad_Guth, Brad.Guth, BradGuth, BG / “Guth Usenet” |
#19
|
|||
|
|||
asteroid close approach, 2011 Nov 08
On 11/1/11 11:15 PM, Brad Guth wrote:
On Nov 1, 9:02 pm, Sam wrote: Brad, get a life! Look at the path of 2005_YU55 with respect to the Earth and Moon http://neo.jpl.nasa.gov/images/2005_...oach_movie.gif Are you jacking off, again? Hey Brad - Seen from a different perspective http://neo.jpl.nasa.gov/images/2005_yu55b.jpg |
#20
|
|||
|
|||
asteroid close approach, 2011 Nov 08
Thank you, Bill and Chris, for sharing your time and expertise in
answering my lunar impact question so thoroughly. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Close approach planetoid. | Sjouke Burry | Misc | 1 | February 5th 08 01:19 AM |
BBC NEWS | Science/Nature | Red Planet set for close approach | Nick | UK Astronomy | 1 | October 29th 05 02:29 PM |
Cassini-Huygens makes first close approach to Titan | Jacques van Oene | News | 0 | October 26th 04 05:06 PM |
Observing 4179 Toutatis near close approach | Astronomy Now Online | UK Astronomy | 1 | September 17th 04 06:02 PM |
Mars Looms Big & Bright as It Nears Record-Breaking Close Approach | Ron Baalke | Misc | 4 | August 10th 03 08:15 AM |