27 January 2012?

Ooops!

"Should have gone to Specsavers..."

"It makes it in to the top 20 closest approaches, but it's sufficiently far away... that there's absolutely no chance of it hitting us," he told the BBC."

Yes, but next time around ...............................?

How about a vote on where you would prefer it to impact? I have some ideas.

I thought at first you might be talking about the one that exploded over California the day before yesterday (April 22rd, 2012).

Space Weather News for April 23, 2012

http://spaceweather.comSIERRA FIREBALL DECODED: An explosion over California that rattled homes across at least two states on Sunday, April 22nd, has been analyzed by NASA's Meteoroid Environment Office: It was a natural meteoroid the size of a mini-van. Analysts say the space rock exploded in the atmosphere with an energy equal to nearly 4 kilotons of TNT and might have sprayed the Sierra Nevada mountains with meteorites. Visit http://spaceweather.com for more information

It was loud enough that I went outside to see if I could see anything... I couldn't! The noise kept up for many seconds, but I couldn't tell where it was coming from, except that it was generally SE from my home... I've never heard anything quite like it!

You can bet the rock hunters are canvassing those mountains in hope of scoring some space rock. If it really was the size of a mini-van, there will probably be some large pieces.

So the asteroid did actually miss.

Looks like we were about to witness a near-hit

Actually, the guys at NORAD probably have a pretty good idea of where it went and what happened to it. They're just not saying because their rock hunters want to get there first.

Bingo!

Update: Someone found some pieces of the meteorite.

http://www.pddnet.com/news-meteorites-found-in-ca-along-path-of-fireball-042612/?et_cid=2615511&et_rid=45605603&linkid=http%3a%2f%2fwww.pddnet.com%2fnews-meteorites-found-in-ca-along-path-of-fireball-042612%2f

Cheers !

Oh My Gosh! that's less than 8 miles from my house, and farther away from the supposed entry site than my house! I guess I better go out and look more carefully!

Thanks!

Well, I can't prove anything easily or quickly, but I did find this:

resting on a sprinkler head in the middle of a lawn...

The image appears redder than the actual stone. That may be because the sun was low in the sky (6PM local time), and/or because of reflections from the yellow paper I used as a background.

I couldn't see any evidence of impact, but it might have bounced from a significant distance. We've had 1.7" of rain in the last 24 hours, so any impact dust would have been washed away. Too bad I didn't think to look a couple of days ago...

I just got back from showing the rock to our prominent local geologist. After looking at it under a microscope, he thinks it's authentic - a carbonaceous chondrite. No chemical analysis yet, but...

Since the geologist confirmed that indeed I may well have found a piece of the meteoroid, I decided to take a closer look. At my age, I can't see a lot of detail without help, so I went out with my loupe and camera. Here are two views of the place where I found the fragment. Although I've added comments & ovals to point out locations, the photos are un-adulterated except for reduction in detail to allow posting here on CR4.

Looking SouthEast:

Looking NorthWest:

That's pretty cool. Not too many people can claim to have found "fresh" space rock.

Cheers!

Indeed! I'm still learning more... As I learn, I'll post more info here.

Thanks again!

I just realized I haven't updated this. Although the geologist thought the material looked right, he was comparing the appearance of the cracked surface of my sample to that of a section cut through a meteorite from Puebla, Mexico. When I sent my photos to two different meteorite experts, they both said it was not a meteorite.

The original map from NASA indicated entry into the atmosphere about 75 SSE from my home; later data show entry about 75 mi ENE of here.

It is interesting to note that I thought the sound came from the SE of my home, when in fact the meteor passed from NE to NW of my home. I do live on the south side of a ridge, so the sound had to have been modified by diffraction by that ridge and/or reflection off other nearby hills.

My conclusion is that my rock must have been thrown there by a fellow weed-eating on a neighbor's property.

It is very interesting to think about the duration of the sound: The first sound you hear must be the one that traveled the shortest distance, as the meteor passed the perpendicular to its trajectory. The last sound you hear must have been the one that traveled the greatest distance; which means the first sound of entry into the atmosphere, or perhaps the sound created when the meteor exploded from the heat of entry. I now gather that this occurred not too far from Reno, or about 75 miles from here. It would have taken a little over a minute for the sound to travel that distance.

"I now gather that this occurred not too far from Reno, or about 75 miles from here. It would have taken a little over a minute for the sound to travel that distance."

Taking speed of sound as about 750 mph, I make that 6 minutes, not 1 minute.

Have you factored in the sound of a supersonic object's bow and stern wave? In other words the sound lags behind the object, just like a boat on water, giving the well known "double-bang."

The idea of an object travelling at high supersonic speed, but slowing rapidly due to air friction and finally exploding, needs a sound experts' (and maybe a ballistics experts') analysis. Anybody out there - help? If you factor in hills around you, I suspect the sound(s) could approach the observer from almost any direction.

P.S When living in the south of England in the 1970's, we used to hear a deep rumble several times per week at about 9.15 pm. It was a mystery for quite a long time. Eventually it was traced to an Air France Concorde, flying supersonically from Rio de Janiero up through the English Channel on its way to Paris. Although about 200 miles away, the sound was reflected off the upper atmosphere back down, much further than would be expected.

I didn't really expect anyone to pay much attention, but since you did, here's my more complete analysis. This was done when I was still under the impression that the point of entry was east of Modesto, but the distance to Reno is very close to the same distance, so the numbers remain valid. Does this sound reasonable?

"An interesting thing about the sound: My initial assumption (and I suspect that of most people) was that the first sound heard from the passing meteor was the sound either of it entering the atmosphere or of it exploding. But it only takes a little thought and a little understanding of physics to see that can't be. These objects approach Earth with velocities generally of tens of thousands of miles per hour - much faster than the speed of sound. By the time they have passed through enough atmosphere to heat up and explode or generate sound, they will have slowed significantly, but I suspect that they are still traveling several thousand miles per hour. I'm estimating that the average velocity between entry or explosion and landing is around 1000 mph.

According to the map above, the explosion occurred over La Grange, Ca., a distance of roughly 75 miles from here. At that speed, the meteor would take 75/1000 of an hour, or 4.5 minutes to travel from La Grange to here. The speed of sound varies with altitude, humidity, and other factors, but 750 mph is a reasonable rough value. At that speed, the initial sound will have taken 75/750 of an hour, or 6.0 minutes to reach here. On its way to Lotus, the main cluster of fragments will have passed about 4 miles from my home. I don't know if it was still travelling at supersonic speed by then, but it was certainly still making noise. That noise will have taken 4/750 of an hour, or roughly 0.3 minutes, or 20 seconds, to get here. So from the time of the explosion, it would have taken 4.5+0.3=4.8 minutes for the first sound to reach me, and 6.0 minutes for the sound from the initial explosion to reach here. That means I should have heard sound for a total of about 1.2 minutes, with the last sound heard being that generated by the explosion. Of course that last sound has spread out in all directions while travelling the 75 miles, so will be much weaker than the initial sound that only had to travel 4 miles.

In fact, I gave up trying to figure out what was causing the sound after about one minute, so was no longer paying attention, and may well have been back inside by the time that sound got here. All of this would seem to confirm that my estimate of 1000 mph average is in the right ballpark!"

This object was supposedly only 3-4 meters across, so the bow and stern waves will have been too close together to distinguish as separate 'booms'. At, say 2000 mph, the two would be around 4 millseconds apart. It has been a number of years now, but I definitely do remember hearing the "double-bang".

I agree with your penultimate paragraph. In fact I rather doubt that they explode at all. It seems to me that the outer layers will ablate long before enough heat can transfer anywhere near the center. The fact that the largest pieces they found of this meteor were around 17 grams, of something closer to 17 Tonnes initial weight, seems to confirm that most of it is vaporized and/or turned to dust. Likewise, the pieces found were scattered over an area only a few miles across. If it had exploded, I would expect a much larger scatter area. Here is the scatter area, according to wordpress.com:

I applaud you for following through with this. Most people would soon lose interest and move on. Natural phenomena can be very fascinating and intriguing. Often there are no ready explanations because no-one has bothered to study it or discuss it, and the incidences are too rare and completely unpredictable. I think your analysis is very good. It demonstrates very well how the observer (listener?) would hear the events occurring in the wrong order and would have much trouble in relating them to any visual observation. Small wonder that some UFO (if they are real) and aircraft sightings by the "man in the street" are often confusing.

Some years ago I saw a meteor/meteorite apparently streaking vertically downwards (and rapidly expanding) into St. Petersburg, Florida. It looked like a disaster, but nothing was reported! I realised later that what I saw was a meteor/meteorite travelling directly away from me, getting brighter as it burned up, giving me the illusion that it was headed directly downwards. It could have been 100 miles away - no way to tell.

Bear in mind my anecdote about Concorde. The supersonic shock wave, by bouncing off the upper atmosphere, had to travel much further than line-of-sight to be heard 200 miles away.