Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Norwegian skydiver nearly struck by meteorite

nrk.no

Post reply on HN
Print view View original

81–90 of 119 posts

Re: Norwegian skydiver nearly struck by meteorite

#81

Post by jessriedel »

woodchuck64 wrote: post #60

Shouldn't we be expecting a rock that has just been heated to plasma stage by atmospheric friction only seconds earlier to be glowing, steaming or leaving little molten fragments of itself behind? Update: maybe not. The last stage of flight is "dark and cold" according to this: http://www.meteorite-recon.com/en/Meteorite_fusion_crust_1.h...

I imagine the rushing air can cool a rock pretty rapidly. The increase in terminal velocity will also tend to partially counteract the increased volume:surface-area ratio of larger rocks.

Re: Norwegian skydiver nearly struck by meteorite

#82

Post by dredmorbius »

bitL wrote: post #58
dredmorbius wrote: post #46

A related question: what's the probability of an aircraft being struck by a meteor. Seems this question was asked in the wake of the Air France flight 447 disappearance (since resolved as pitot tube freezing combined with pilot error and control feedback failures of the Airbus design). But still, the odds of a strike on _an_ aircraft over the next 20 years are about 4%: http://blog.revolutionanalytics.com/2009/06/how…

That would be under an assumption that the distribution of planes around the globe is even. Given most jetliners are flying in corridors, I would say the actual probability is much much lower. The same can be probably said about meteorites - I guess their geographic distribution is uneven as well.

As others have said: the distribution of the planes over the Earth (and their speed -- one Yahoo site I ran across suggested they're harder to hit because they're moving fast -- that's also irrelevant, not to mention that pretty much everything on Earth is moving at about 20km/s relative to an asteroid) doesn't matter.

Because meteorites aren't aimed. Odds are they'll land pretty much anywhere on the planet.

I'm not entirely sure this is the case -- because the Earth orbits the Sun, the eastward-facing side should be sweeping through more debris than the west, which means that if you could concentrate your flights on that side, you'd be at higher risk. As it is, most flights tend to operate during daylight hours, with the before-noon flights being at greater risk. More reasons to catch the afternoon flight if you prefer to play things safe, or the morning flight if you feel like making history (or low-grade mysteries of the unknown TV programmes).

Re: Norwegian skydiver nearly struck by meteorite

#83

Post by cratermoon »

dclowd9901 wrote: post #47

I'm... skeptical. If you look at the frames of the meteorite falling, it looks like each frame has the fragment at about 3 feet from its last position. If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph. That seems really slow for a rock flying into the atmosphere from space, and far slower than a rock would have to be going for it to "cut him in half." My guess: a rock that fell off the underc…

I am very skeptical. Although quite stupid, it wouldn't be hard for the other guy to have thrown some kind of junk and get it on camera, then claim it was a meteorite.

I bet nobody ever finds any evidence of said "space rock".

Re: Norwegian skydiver nearly struck by meteorite

#84

Post by cratermoon »

simias wrote: post #57
jessedhillon wrote: post #30

Earlier quoted context omitted.

If you look at how a parachute is packed, and how it unfolds when deployed, what you described is definitely not the simpler explanation preferred by Occam's razor.

Well, since it seems I'm in a minority here I'll accept that I might be misjudging the odds on this one, especially since I know nothing about skydiving. I guess it goes to prove that since nowadays we're almost all carrying video recorders with us at all times the probability of catching the most elusive events on video gets increasingly large. I expect to see a video of someone standing at the foot of a rainbow any…

It could have fallen from or (if they are being stupid) been thrown by the other guy, who happens to appear in the frame just after the object.

Re: Norwegian skydiver nearly struck by meteorite

#85

Post by cratermoon »

CodeCube wrote: post #48
ynniv wrote: post #41

Earlier quoted context omitted.

ie, thrown it? That does seem far more likely than it being from space.

If he threw a rock of that size at his buddy ... what a jerk

People are stupid, sometimes. Especially on internet videos.

Re: Norwegian skydiver nearly struck by meteorite

#87

Post by freyr »

dclowd9901 wrote: post #47

I'm... skeptical. If you look at the frames of the meteorite falling, it looks like each frame has the fragment at about 3 feet from its last position. If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph. That seems really slow for a rock flying into the atmosphere from space, and far slower than a rock would have to be going for it to "cut him in half." My guess: a rock that fell off the underc…

>> it looks like each frame has the fragment at about 3 feet from its last position

How did you arrive at this number? What distance do you estimate between the camera and the falling rock?

> If that's a 60fps camera (I think it is?), that's 180 f/s speed or 122mph.

Are you assuming the skydiver is stationary?

Re: Norwegian skydiver nearly struck by meteorite

#88

Post by xenophonf »

stouset wrote: post #59
binarymax wrote: post #7

Earlier quoted context omitted.

It had already entered the atmosphere, and probably slowed down significantly due to friction, then based on its mass it reached a low terminal velocity. https://en.wikipedia.org/wiki/Terminal_velocity

Ram pressure, not friction

To get really technical, it's wave drag. ;) There's a fascinating discussion here:

http://cosmoquest.org/forum/showthread.php?35327-meteors-ram...

Re: Norwegian skydiver nearly struck by meteorite

#89

Post by angusb »

danbruc wrote: post #9
jon_black wrote: post #3

Is it me or does it look like the "meteorite" is moving quite slow. Shouldn't it be moving so fast that you'd need a high speed camera to see it in that detail? Also...his parachute is always above him, maybe it fell out of that.

The article states that the meteorite already slowed down to around 300 km/h because the incident happened at a low altitude and the heavy braking was already over.

I just spent a while looking up the maths on this and was really surprised to find that the terminal velocity of a spherical rock (diameter 10cm, density 2.5g/cm^3) at this altitude is remarkably close to 300 km/h (I got 340).

Aside: up until now I had imagined that if a skydiver were to ever drop a rock of that size (or a dense piece of equipment like a DSLR) during freefall they would never be able to catch it, but as the terminal velocity of a skydiver in "dart" position is about 320km/h that's not the case. Pretty cool.

Re: Norwegian skydiver nearly struck by meteorite

#90

Post by rz2k »

stretchwithme wrote: post #67
rz2k wrote: post #63

Earlier quoted context omitted.

The data are interesting on their own if you start with the idea that meteor strikes are random across centuries, but the information collection and preservation isn't. For instance, with two data points you might claim there were more monks than princes in Renaissance Italy, but they were both surrounded by literate people who kept records compared to the even more numerous peasants. However, I suppose interpreting…

More people are working indoors in tall buildings and traveling in cars. So they are more concentrated where they live and travel. And each sighting is counted only once, regardless of how many people saw it.

Relative to the entire population, humanity is more urbanized, but that seems irrelevant to me compared to how many single square miles on the earth's surface contain a human who is connected to the global community.

While the decreasing number of people needed to farm a square mile seems like it would matter enough to decrease the newsworthiness of meteor strikes in some agricultural regions, it still seems likely that there has been a net increase in total area that includes the lower bound of population density where a meteor strike would be sufficiently newsworthy to make this list.

Take Las Vegas over the past 50 years as an example. It's a prime example of people being increasingly insulated from the outdoors, yet the footprint and total area of settled land has grown dramatically. It hardly matters whether you're inside or not, if a meteor strikes your block.

Edit: I was curious about the data and found this Google Earth file[1]. It looks like there definitely are many more recorded events, and it's just that the bar for being newsworthy has risen. However, what's strange is the preponderance of events in NW Texas and north of there. If records were population-based, then it should look like population density maps. I can't figure out off hand what causes the density of events, other than flat land and maybe tornado observation equipment, but that would seem to apply to other areas as well.

[1]https://productforums.google.com/forum/#!topic/gec-places/59...

Post reply on HN