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A-L-E-X
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25 Feb 2021 00:11

Wow thats absolutely amazing!  Was anyone actually in the area to see this?  I picture something like this happening on the Moon, not on Earth!  It must've been wonderful to witness!

Sometimes I wish our atmosphere was thinner so a lot more of us could see these as they hit, of course then there would be more of an existential threat ;)
 
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25 Feb 2021 00:51

A-L-E-X wrote:
Source of the post Was anyone actually in the area to see this? 

It was cloudy in the area, so all observations were a few 100 km away.

Here's one video we recorded from Norway 400 km away:


The meteor fades at a stunningly low 12 km altitude, where it had decellerated to about 2 km/s.
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26 Feb 2021 18:19

That's a once in a lifetime kind of experience!  But I think you've seen a few like these, haven't you, Mid?  Maybe some parts of the planet are more favorable for these?  Has any research been done into that I wonder?
 
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26 Feb 2021 22:12

A-L-E-X wrote:
Source of the post Maybe some parts of the planet are more favorable for these?

Meteor/meteorite frequency is very uniform across the Earth. Some people might see more than usual over some span of time just by chance. Or if they look up more often, or have an automated observing network like midts has. :)

Just imagine how many more freshly fallen meteorites might be discovered if there were more of these networks operating around the world. But it depends a lot on the remoteness and difficulty of the terrain, too.
 
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27 Feb 2021 08:08

A-L-E-X wrote:
Source of the post But I think you've seen a few like these, haven't you, Mid? 

With my own eyes, no.  I've seen my own shadow from a bright meteor, and I've seen fragmenting meteors, but I've not seen a truly huge fireballs (this one had a peak magnitude of -18 or -19 (normalised for 100 km distance)), which might be a once of a lifetime experience.  Such bright fireballs will be visible every few years where ever you live, but you will miss them most of the time because your asleep or simply indoors.
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27 Feb 2021 10:37

A-L-E-X wrote:
Source of the post Maybe some parts of the planet are more favorable for these?  Has any research been done into that I wonder?

A lot of research indeed and everything seems to corroborate that they indeed fall everywhere on Earth. Since the fall of a meteor doesn't depend on the particular point of Earth's rotation all longitudes are equally probable to witness the event. One might say that all latitudes are not equally probable because meteors like any solar system object that move near the ecliptic might fall more frequently near the ecliptic projection on Earth's surface, but since 1) Earth's equator (and thus it's rotation plane) is misaligned with the ecliptic 2) asteroids are not all really on the ecliptic and 3) the range of inclinations of meteoroids makes the concept of an ecliptic somewhat fuzzy since the Earth is much much smaller than the width where we can find the vast majority of objects of the Solar System. Thus, in conclusion, there's no latitudinal preference either. Each spot on Earth has the same probability to be hit by an object. But this is theory (which makes quite a LOT of sense). How about empirical data? Well here you have it

Image

As you can see, there's not even a preferred time of the day (half fall at night and half during the day). They really can come and hit any place of the planet. There are some biases at play when we thing of "more probable locations": for example, many important meteor strikes happened in Siberia (Tunguska, Sikhote Alin etc...), but people tend to forget that Russia is one of the largest surface areas on Earth that we can scout. Another bias might be the arctic and Antarctica since a lot of meteor search is done over the ice, where the dark material might be in clear contrast with the icy landscape. But this is only observational biases, the truth is that they fall everywhere with equal probability.

Image

Some studies focus on impact craters instead of bolide sightings. As you can see on the Moon there's no particular preference in terms of latitude. On Earth things are much more complicated since tectonic activity and erosion have played a role in erasing impact craters in regions that are younger. But there are studies which focus on correcting this bias by counting the impact craters in regions of the planet with different ages and estimate their original count (before the region suffered certain degree of erosion). And the result is the same, large objects have collided with our planet from every direction in a totally isotropic way.
 
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28 Feb 2021 00:17

Watsisname wrote:
A-L-E-X wrote:
Source of the post Maybe some parts of the planet are more favorable for these?

Meteor/meteorite frequency is very uniform across the Earth. Some people might see more than usual over some span of time just by chance. Or if they look up more often, or have an automated observing network like midts has. :)

Just imagine how many more freshly fallen meteorites might be discovered if there were more of these networks operating around the world. But it depends a lot on the remoteness and difficulty of the terrain, too.

I was thinking that too, but a part of me wondered if the geometry of the earth and the typical inclination of solar system objects might favor some locations over others (or the concept that some parts of the planet have a slightly stronger gravitational pull than other parts.....but I suspect this is insignificant when compared to drawing in something from millions of miles away?)
I bet the majority of these fall over the open waters since we're 70% water.  It just makes it all the more exciting to get to witness something like this.  I remember when I felt my first and only earthquake here in NY in the middle of the day back in August 2011 (that's the famous one that was centered in Virginia at 5.8 with videos clearly showing animals at the National Zoo behaving unusually about 30 minutes prior to the quake which made the visitors very uneasy, and a week later we were hit by Hurricane Irene, which remarkably duplicated a similar occurence back in 1944 when NY was hit by a 5.8 earthquake [back then people were worried the Nazis were attacking]  and then hit a week later by the famous 1944 hurricane.)  I felt an irrational sense of excitement when I felt the August 2011 quake, instinctively knowing this must be an earthquake, although I had never experienced one before (knowing full well how dangerous an earthquake can be!)  It's the kind of excitement one feels at seeing something that might be a once in a lifetime event for that person.  This meteorite strike was even more rare.
 
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28 Feb 2021 00:25

FastFourierTransform wrote:
A-L-E-X wrote:
Source of the post Maybe some parts of the planet are more favorable for these?  Has any research been done into that I wonder?

A lot of research indeed and everything seems to corroborate that they indeed fall everywhere on Earth. Since the fall of a meteor doesn't depend on the particular point of Earth's rotation all longitudes are equally probable to witness the event. One might say that all latitudes are not equally probable because meteors like any solar system object that move near the ecliptic might fall more frequently near the ecliptic projection on Earth's surface, but since 1) Earth's equator (and thus it's rotation plane) is misaligned with the ecliptic 2) asteroids are not all really on the ecliptic and 3) the range of inclinations of meteoroids makes the concept of an ecliptic somewhat fuzzy since the Earth is much much smaller than the width where we can find the vast majority of objects of the Solar System. Thus, in conclusion, there's no latitudinal preference either. Each spot on Earth has the same probability to be hit by an object. But this is theory (which makes quite a LOT of sense). How about empirical data? Well here you have it

Image

As you can see, there's not even a preferred time of the day (half fall at night and half during the day). They really can come and hit any place of the planet. There are some biases at play when we thing of "more probable locations": for example, many important meteor strikes happened in Siberia (Tunguska, Sikhote Alin etc...), but people tend to forget that Russia is one of the largest surface areas on Earth that we can scout. Another bias might be the arctic and Antarctica since a lot of meteor search is done over the ice, where the dark material might be in clear contrast with the icy landscape. But this is only observational biases, the truth is that they fall everywhere with equal probability.

Image

Some studies focus on impact craters instead of bolide sightings. As you can see on the Moon there's no particular preference in terms of latitude. On Earth things are much more complicated since tectonic activity and erosion have played a role in erasing impact craters in regions that are younger. But there are studies which focus on correcting this bias by counting the impact craters in regions of the planet with different ages and estimate their original count (before the region suffered certain degree of erosion). And the result is the same, large objects have collided with our planet from every direction in a totally isotropic way.

Thanks this is all fascinating!  I figured most of the falls would occur over the ocean since our planet is 70% water.  But I also wondered with the slight variations in gravity across our planet, if some particular locations might be prone to them (sort of like how some people are prone to getting hit by lightning because of their iron content.)  I can see from these maps that isn't the case.  But this is still interesting research.  In the previous post I mentioned about experiencing a freak earthquake and then an east coast hurricane a few days later and then finding out something similar had happened in 1944 too, which made me interested in finding out if this could be more than a coincidence.  Those events most likely were but imagine my surprise at finding out that researchers in Japan and Mexico had conducted research on this and they think there might be a slight chance that big tropical cyclones and earthquakes might be linked (but it would have to be near a major fault line.)  I've also read about earthquake weather which I always had thought was coincidental but then read that it could be possible, since there are sometimes gas emissions that happen from the earth just before an earthquake and which sometimes lead to unusual cloud formations?  All pretty interesting stuff for "nerds" like us!
 
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28 Feb 2021 00:28

midtskogen wrote:
A-L-E-X wrote:
Source of the post But I think you've seen a few like these, haven't you, Mid? 

With my own eyes, no.  I've seen my own shadow from a bright meteor, and I've seen fragmenting meteors, but I've not seen a truly huge fireballs (this one had a peak magnitude of -18 or -19 (normalised for 100 km distance)), which might be a once of a lifetime experience.  Such bright fireballs will be visible every few years where ever you live, but you will miss them most of the time because your asleep or simply indoors.

I wish to experience one of these one day.  I remember reading something somewhere about the brightest fireball reliably recorded was somewhere in the -21 to -23 range in then Czechoslovakia sometime back in the early 1970s?  That should easily be visible by broad daylight and even cast shadows!

By the way it's nice to see all of you back posting again over the past few days!  I was getting somewhat concerned as there hadn't been much traffic on here in awhile before that.
 
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28 Feb 2021 07:00

A-L-E-X wrote:
Source of the post but a part of me wondered if the geometry of the earth and the typical inclination of solar system objects might favor some locations over others (or the concept that some parts of the planet have a slightly stronger gravitational pull than other parts.....but I suspect this is insignificant when compared to drawing in something from millions of miles away?)

Yes, the variations in Earth's gravitational field are far too small to cause any noticeable effect on meteor strikes. Meteor paths aren't affected as much by Earth's gravity as you might think, anyway, because they move so fast. Most meteors that hit Earth were not so much "pulled in", but rather the Earth simply got in their way. 

We can actually make that claim rigorous. We can calculate the "effective cross section" of the Earth, meaning the area of the target Earth presents for a potential impactor when we factor in its gravity (so it must be larger than the actual Earth itself.) To do that, we find the "impact parameter" (the minimum approach distance an asteroid would have if we ignored Earth's gravity) such that when we do factor in the gravity, it comes closer and ends up just grazing Earth's surface. Then the Earth's effective cross section is pi times the square of the impact parameter (just like finding the area of a circle whose radius is the impact parameter.)

This page on spaceacademy goes through the calculation and has a nice table summarizing these values for a given range of asteroid speeds (both the "far-away" speed, and the speed at impact). Intuitively, the greater the speed, the smaller the Earth's effective cross section is, because at higher speeds there is less time for Earth's gravity to have an effect on the path.

Now let's check at what speed the effective cross section of the Earth is doubled. If the area is doubled, that means half the strikes happen because they would have missed but Earth's gravity pulled them in, and the other half would have hit anyway. According to the table, this happens when the "faraway" speed is between 10 and 15 km/s, or an impact speed of between 15 and 19 km/s. As it turns out, the area is exactly doubled when the "faraway" speed equal to Earth's escape speed, 11.18km/s. That gives an impact speed of 15.8km/s. 

But wait. The average impact speed of asteroids on the Earth is faster -- about 17km/s. And comets strike even faster still. That means for the average impact, Earth's effective cross section was less than double its actual cross section. Therefore there was a greater than 50% chance the impact would have happened even without Earth's gravity playing any role. Earth was simply in the way.

A-L-E-X wrote:
Source of the post (sort of like how some people are prone to getting hit by lightning because of their iron content.)

Where did you hear that? I am quite sure it is not true. At the very least, I have never seen any reputable study connecting lightning strike risk to iron in the body. And it would be almost impossible to determine from data, since there are so many other factors that matter more.

The amount of iron in a person is very small (a few thousandths of a percent), so I doubt that would play any significant role in our conductivity. But perhaps the more important lesson is that iron does not attract lightning, anyway. Lightning strikes are determined by what "sticks out" from the surrounding environment. (Something which is well described and visualized in this XKCD "What if?" comic.) This is also a very general feature of electric arcs: they tend to form at sharp points on a conductor, because sharp points are where electric field is maximized. That's the basis of how lightning rods work, and also why we try to make conductors as smooth as possible when we want to prevent arcs from forming.

So don't worry about iron in your body when it comes to lightning. Worry instead about being in a vulnerable situation when there is lightning nearby. Basically, don't be the tallest thing around, or close to the tallest thing around.
 
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01 Mar 2021 04:02

Watsisname wrote:
A-L-E-X wrote:
Source of the post but a part of me wondered if the geometry of the earth and the typical inclination of solar system objects might favor some locations over others (or the concept that some parts of the planet have a slightly stronger gravitational pull than other parts.....but I suspect this is insignificant when compared to drawing in something from millions of miles away?)

Yes, the variations in Earth's gravitational field are far too small to cause any noticeable effect on meteor strikes. Meteor paths aren't affected as much by Earth's gravity as you might think, anyway, because they move so fast. Most meteors that hit Earth were not so much "pulled in", but rather the Earth simply got in their way. 

We can actually make that claim rigorous. We can calculate the "effective cross section" of the Earth, meaning the area of the target Earth presents for a potential impactor when we factor in its gravity (so it must be larger than the actual Earth itself.) To do that, we find the "impact parameter" (the minimum approach distance an asteroid would have if we ignored Earth's gravity) such that when we do factor in the gravity, it comes closer and ends up just grazing Earth's surface. Then the Earth's effective cross section is pi times the square of the impact parameter (just like finding the area of a circle whose radius is the impact parameter.)

This page on spaceacademy goes through the calculation and has a nice table summarizing these values for a given range of asteroid speeds (both the "far-away" speed, and the speed at impact). Intuitively, the greater the speed, the smaller the Earth's effective cross section is, because at higher speeds there is less time for Earth's gravity to have an effect on the path.

Now let's check at what speed the effective cross section of the Earth is doubled. If the area is doubled, that means half the strikes happen because they would have missed but Earth's gravity pulled them in, and the other half would have hit anyway. According to the table, this happens when the "faraway" speed is between 10 and 15 km/s, or an impact speed of between 15 and 19 km/s. As it turns out, the area is exactly doubled when the "faraway" speed equal to Earth's escape speed, 11.18km/s. That gives an impact speed of 15.8km/s. 

But wait. The average impact speed of asteroids on the Earth is faster -- about 17km/s. And comets strike even faster still. That means for the average impact, Earth's effective cross section was less than double its actual cross section. Therefore there was a greater than 50% chance the impact would have happened even without Earth's gravity playing any role. Earth was simply in the way.

A-L-E-X wrote:
Source of the post (sort of like how some people are prone to getting hit by lightning because of their iron content.)

Where did you hear that? I am quite sure it is not true. At the very least, I have never seen any reputable study connecting lightning strike risk to iron in the body. And it would be almost impossible to determine from data, since there are so many other factors that matter more.

The amount of iron in a person is very small (a few thousandths of a percent), so I doubt that would play any significant role in our conductivity. But perhaps the more important lesson is that iron does not attract lightning, anyway. Lightning strikes are determined by what "sticks out" from the surrounding environment. (Something which is well described and visualized in this XKCD "What if?" comic.) This is also a very general feature of electric arcs: they tend to form at sharp points on a conductor, because sharp points are where electric field is maximized. That's the basis of how lightning rods work, and also why we try to make conductors as smooth as possible when we want to prevent arcs from forming.

So don't worry about iron in your body when it comes to lightning. Worry instead about being in a vulnerable situation when there is lightning nearby. Basically, don't be the tallest thing around, or close to the tallest thing around.

It was from another science forum but I see the person was mistaken.  I looked for research on body metal content and there is no research connecting it.  As a matter of fact, there isn't even a connection between external metal content or proximity to metal objects and more of a likelihood of lightning strikes.  It looks like lightning is most likely to seek tall pointy objects (of any composition, not just metal), which is a good reason not to shelter under a tree!  There are certain occupations which may make lightning strikes more likely, just because of the amount of time spent outdoors and proximity to tall pointy objects like trees- Roy Sullivan is a case in point- he was struck by lightning 7 times.


https://en.wikipedia.org/wiki/Roy_Sullivan


He met with a really sad ending :(
Did you read what happened to him?


Roy Cleveland Sullivan (February 7, 1912 – September 28, 1983) was a United States park ranger in Shenandoah National Park in Virginia. Between 1942 and 1977, Sullivan was hit by lightning on seven occasions and survived all of them. For this reason, he gained the nicknames "Human Lightning Conductor" and "Human Lightning Rod". Sullivan is recognized by Guinness World Records as the person struck by lightning more recorded times than any other human being.[3]


Contents
1 Personal life
2 Seven strikes
3 Statistics
4 See also
5 References
6 External links
Personal life
Roy was born in Greene County, Virginia, on February 7, 1912. He started working as a ranger in Shenandoah National Park in 1936.[4] Sullivan was described as a brawny man with a broad, rugged face, who resembled the actor Gene Hackman. He was avoided by people later in life because of their fear of being hit by lightning, and this saddened him. He once recalled "For instance, I was walking with the Chief Ranger one day when lightning struck way off (in the distance). The Chief said, 'I'll see you later.'"[5]

On the morning of September 28, 1983, Sullivan died at the age of 71 from a self-inflicted gunshot wound to the head.[6] Two of his ranger hats are on display at two Guinness World Exhibit Halls in New York City and South Carolina.[2]




About the escape velocity research, I find that absolutely fascinating!  So the asteroid faraway speed is just slightly more than earth's escape speed, but it's enough to show that impacts are more due to the earth getting in the way, which makes sense, because at that speed, the earth's gravity  doesn't have enough time to influence the asteroid's trajectory.  And I think you also showed before that the moon doesn't have much of an influence either in "deflecting" them away from us, except for whatever protection it can offer by "getting in the way."  So it would only give us a marginal protection and wouldn't have influenced the start of life on Earth much in that way but moreso with its impact on the tides and allowing life to transition over to land.
 
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midtskogen
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26 Jul 2021 01:38

Veeery busy day yesterday, complete media storm leaving little time to work out the meteor track.

Meteor lights up the night in Norway

Powerful air blast.  One fractured window reported, otherwise no serious damage.  I had just fallen asleep and didn't notice a thing, though my geophones in my basement picked up quite a bit of shaking.

Preliminary results.  (The website was extremely slow yesterday due to heavy traffic, my uplink is too slow...)
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A-L-E-X
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26 Jul 2021 02:36

midtskogen wrote:
Veeery busy day yesterday, complete media storm leaving little time to work out the meteor track.

Meteor lights up the night in Norway

Powerful air blast.  One fractured window reported, otherwise no serious damage.  I had just fallen asleep and didn't notice a thing, though my geophones in my basement picked up quite a bit of shaking.

Preliminary results.  (The website was extremely slow yesterday due to heavy traffic, my uplink is too slow...)

early Perseids?  I am excited about the shower this year, the moon is in  a good phase and will be setting before midnight during peak week and I took a whole week off to be in the mountains from Saturday August 7th through Monday August 16th to see this amazing shower!
 
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26 Jul 2021 04:24

A-L-E-X wrote:
Source of the post early Perseids?

No, Perseids are fast and disintegrate at high altitude.  This one came at about 15 km/s and faded low at 23.5 km altitude.  Also, it had an Aten type orbit mostly confined within Earth's orbit, which makes it quite rare.
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A-L-E-X
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26 Jul 2021 04:59

midtskogen wrote:
A-L-E-X wrote:
Source of the post early Perseids?

No, Perseids are fast and disintegrate at high altitude.  This one came at about 15 km/s and faded low at 23.5 km altitude.  Also, it had an Aten type orbit mostly confined within Earth's orbit, which makes it quite rare.

Wow, very interesting event.  Did you have one like this last year around this time too?
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