Note: This comment became long, for the short summary without the analysis and discussion, go to the summary at the end.
Following the link in the post, I found:
There is a video, I can embed, but it is available in the article. The above has a map of the state and marked the area.'It was just insanity': Loud, mysterious boom lights up West Michigan skies
Dozens of people reported a billowing sound lasting over a minute long, reminiscent of a passing train
As families prepared for bed late Thursday night, streaks of light lit up the skies above Kent and Ottawa counties. The mysterious sight was accompanied by a loud boom that lasted over a minute long and shook the ground.
As families prepared for bed late Thursday night, streaks of light lit up the skies above Kent and Ottawa counties. The mysterious sight was accompanied by a loud boom that lasted over a minute long and shook the ground.
Thursday night round the time of publishing was August 10 in the US. This year, the Perseids can be observed between July 14 and September 1, with a peak on August 13.
The colour of the observed event was orange, most Perseids are orange to yellow, so that fits. What fits much less well is the sound. Here are the reports again:
Here is what the AMS person says about sound:
The speed of the Perseids is 58.8 km per second. That is fast for a meteor shower, as one can confirm by comparing with this List of meteor showers, where speeds vary between 16 and 70 km/s. High speed means that the object does not linger for a long time, I looked at calculated orbits and speeds for Perseid specimens. Here is an example from www.stjerneskud.info where a meteor starts is captured by the camera at an altitude of 110 km and vanishes at an altitude of 70 km.
As the meteor meets resistance from the air, the speed drops:
The above examples shows the speed was only significantly reduced below an altitude of 80 km, and the whole event was over in less than 1.3 seconds. That is not a long time, and does not match with what was observed about the duration of the sound in the US event. There are several other Perseides observations on the above site, and this was the longest lasting out of a number I looked at. Also, if one goes into the database one notices that there are other meteors that have been observed during the Perseides season, but which are not Perseides. And if one goes through the list, it is not uncommon to observe bright meteors which are not part of the shower that is listed for a particular time. The sound in the video is also different from other fireball caused booms, like this:
Meteor makes loud boom as it travels across Utah sky
One question is what happens when the meteor cameras lose contact with the meteors. If observation conditions are not limiting, like artificial lights or natural sources like the full moon, obstacles in the location like trees, hills, houses, mountains, and clouds, a meteor may disappear because it turned into dust completely or was extinguished, because the speed went down, with that the temperature also decreased, and the materials stopped glowing.
If the object survives the atmosphere, but does not glow, the continued passage is called the dark flight, as in this study: Dark-flight Estimates of Meteorite Fall Positions: Issues and a Case Study Using the Murrili Meteorite Fall, or see the slides from 2011 presented by a member of the Croatian Meteor Network. Dark Flight Calculations - How accurate can they be? by Željko Andreić which basically shows that once the fireball is extinguished, it won't go too far. Here is an interesting video recorded by a skydiver in Norway, who might have caught a meteor during dark flight on its way to become a meteorite. One can laugh at the video, but having looked at his FB, I would say, he would be the kind of person who might be gifted with such an experience.
From what altitude would a sonic boom still be audible at sea level? - from below 50 km or so.
There was
Using Sonic Booms to Locate Meteorites Sounds Produced by Meteors - Strewnify
At an altitude of 50 km there is not much air, from answers.com there was
See also this illustration from Change in the Atmosphere with Altitude - Air pressure changes with altitude.
For further clarification, here are different altitudes of the Earth Atmosphere:
How far away can the boom be heard? Does it make a difference what shape and size the object has?
This is not from how high up, but the overall area to the sides. From NASA Armstrong Fact Sheet: Sonic Booms
A small stone size meteor would not create much of a boom, if any, but the bulky Space Shuttle did.
Applying the knowledge of sonic boom altitude to sonic boom audible area
If a sonic boom can be created at an altitude of 50 km and a sonic boom spreads over an area that is about 1 mile for every 1000 ft of altitude, asa a rule of thumb, then a boom at an altitude of 50 km, corresponding to 164,042 ft might cover an area of 164 miles, which is 264 km, or 130 km to each side. On the other hand, if we hear a sonic boom, and from reports can estimate it covers a wide area of say 64 km or 40 miles, then we can estimate that the boom took place at an altitude of 40,000 ft. However, this might not be exact if the boom is in fact continuous due to passage at supersonic speed, as in a plane.
A sonic boom is not a one-off, it can be heard along the path or trajectory as long as the speed of the object is supersonic.
In this discussion thread there was
Influence from the air temperature on the speed of sound, and how the conditions of the ground may affect the sound of the sonic book
I listened to the sound of the event, and it might be something that is not really a usual sonic boom, but more related with the strange sounds in the sky that are sometimes heard. It does not mean the event was not accompanied by some meteoric activity, but it is not a typical boom.
There is a phenomenon related to electricity. The Guardian wrote in 2003
The sound of shooting stars
I tried to find out how the above idea progressed. One study suggested that you need an astronomical magnitude of -10 to observe the VLF effects. Venus at its brightest is about -5. A magnitude of -10 would mean the object needs to be about 100 times brighter than Venus at its brightest. A newer study did not find any VLF effects for events up to -7.8. Therefore, if this event and the sounds were related to electromagnetic activity, then it could have been pretty powerful.
Summary of ideas
- The sound of the object in Michigan does not correspond to a typical meteor, nor did the duration of the sound.
- Meteors and fireballs can appear during the time window of a particular meteor shower without belonging to the shower. In this case, if it was a meteor that created the sound etc. it did not have to be a Perseide , which are quite fast with averages close to 59 km/s on entry.
- When a meteor stops shining on the way in, assuming it does not just fly through the atmosphere, it has either been turned to dust, or it has lost so much speed it can no longer shine. If a meteor has material, but no light, and is on the way to fall on Earth, the last leg of the journey in space is called dark flight. It is studied by meteorite hunters, because the beginning of the dark flight phase means the destination is near.
- Sonic booms can only happen if there is enough air, the limit is an altitude of around 50 km.
- A sonic boom will be more pronounced if the object causing it, is larger and bulky. A small object may not create anything audible far away.
- A sonic boom will be heard throughout the passage, as long as the speed of the object exceeds that of the speed of sound at the location of the observer.
- A sonic boom can propagate and roughly cover a mile in width for every 1000 feet of altitude the object causing the boom is located.
- Meteors at least 100 times brighter than Venus at its brightest have been observed to produce VLF waves that some sensitive people can pick up and "hear".
#Argentina A meteorite fall was recorded in the city of Bariloche
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