2027: "Lightning Distance"

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2027: "Lightning Distance"

Postby pebkac » Wed Aug 01, 2018 12:27 pm UTC

Image
Title text: "The index of radio refraction does have a lot of variation, which might throw off your calculations, so you can also look at the difference in brightness between the visible flash and more-attenuated UV and x-rays."

So I've been doing it wrong all this time! I used to count between seeing the the flash and hearing the rumble, which, when divided by the distance, tells you how fast you counted.

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Re: 2027: "Lightning Distance"

Postby Wee Red Bird » Wed Aug 01, 2018 12:56 pm UTC

I remember, as a kid, being told the number of seconds between the flash and rumble is the number of miles away it is.
In reality, one second is a fifth of a mile away. The lightning strike is closer than you think.

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Re: 2027: "Lightning Distance"

Postby jc » Wed Aug 01, 2018 1:32 pm UTC

And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

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Re: 2027: "Lightning Distance"

Postby The Moomin » Wed Aug 01, 2018 1:38 pm UTC

Luckily we're in a house built on an ancient Indian burial ground so we'll have been sucked into the other side before the storm hits.
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Re: 2027: "Lightning Distance"

Postby speising » Wed Aug 01, 2018 1:38 pm UTC

jc wrote:And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

or rather, take the seconds times 3, which is closer to reality.

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Re: 2027: "Lightning Distance"

Postby Keyman » Wed Aug 01, 2018 2:54 pm UTC

Wee Red Bird wrote: The lightning strike is closer than you think.
Pshaw! You're just timing it in your ear view mirror.
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Re: 2027: "Lightning Distance"

Postby Sableagle » Wed Aug 01, 2018 3:07 pm UTC

Isn't it 350 m/s?

Oh good grief. When I started to google it, the search bar popped up a list of suggested searches and not one of them mentioned a particular altitude.

From fighterplanes.com:
The speed of sound is not a constant, but depends on altitude (or actually the temperature at that altitude). A plane flying Mach 1.0 at sea level is flying about 1225 km/h (661 Knots, 761 mph), a plane flying Mach 1.0 at 30000 ft is flying 1091 km/h (589 knots, 678 mph) etc.


... and from NASA:
Image

The speed of sound is a constant within a given gas and the value of the constant depends on the type of gas (air, pure oxygen, carbon dioxide, etc.) and the temperature of the gas. An analysis based on conservation of mass and momentum shows that the speed of sound a is equal to the square root of the ratio of specific heats g times the gas constant R times the temperature T.

a = sqrt [g * R * T]


Speeds in m/s, from sea level up, 1 km at a time: 340, 336, 332, 328, 324, 320, 316, 312, 308, 303, 299, 295, 295, 295, 295, ..... up to 305 at 30 km.

Hypsographic demography

As of 1994, an estimated 1.88 × 109 people, or 33.5% of the world’s population, lived within 100 vertical meters of sea level, but only 15.6% of all inhabited land lies below 100 m elevation. The median person lived at an elevation of 194 m above sea level. Numbers of people decreased faster than exponentially with increasing elevation.


It may be closer to 300 m/s for most of the Earth's atmospheric depth, but for where people live I'd stick with 350 m/s.

If you really want to know the distance, though, you ought to coordinate with others around your region and install a grid system of radios to detect the EM pulses from the lightning strikes and map them by time difference of arrival. Your grid needs to be large enough to get wide angles between lines of possible origin from the various receiver pairs in it and also dense enough to map each strike before another occurs.

Alternatively, you could go with the helicopter pilot's approximation: if it's close enough for you to hear the thunder, it's close enough for you to get hit by the lightning.
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Re: 2027: "Lightning Distance"

Postby Heimhenge » Wed Aug 01, 2018 4:11 pm UTC

Important to note the sound wave from the lightning can be delayed, advanced, or refracted away. I've seen lightning that was definitely close enough to hear but remained silent (well, maybe not totally silent ... the rain can get kinda noisy). And then there's the reflected waves, smeared out into a rumble, that can also muddy your counting.

A bit simplistic but was fun to animate: http://sky-lights.org/2014/07/28/what-causes-thunder/

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Re: 2027: "Lightning Distance"

Postby gmalivuk » Wed Aug 01, 2018 4:52 pm UTC

Sableagle wrote:Oh good grief. When I started to google it, the search bar popped up a list of suggested searches and not one of them mentioned a particular altitude.
You must have trained your Google to be dumb. When I type "speed of sound" it does the calculator thing where the top "suggestion" is the number Google calculates (343 m/s). When I type "speed of sound at" the top completion is "sea level".

If you really want to know the distance, though, you ought to coordinate with others around your region and install a grid system of radios to detect the EM pulses from the lightning strikes and map them by time difference of arrival. Your grid needs to be large enough to get wide angles between lines of possible origin from the various receiver pairs in it and also dense enough to map each strike before another occurs.
Or, of course, you could join a group of people who already do that.
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Re: 2027: "Lightning Distance"

Postby Mikeski » Wed Aug 01, 2018 5:05 pm UTC

The important part of timing lightning is: "Did the lights in your house go out in time with the flash"?

Then you need to call the power company.

If you're in a situation like the comic, where the lightning bolt persists long enough to have an entire conversation about it, a call to your religious professional may be required, to see if there was an Armageddon scheduled.

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Re: 2027: "Lightning Distance"

Postby Soupspoon » Wed Aug 01, 2018 5:32 pm UTC

If you count the time between hearing the flash and seeing the rumble, it tells you how synaesthesic you are.

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Re: 2027: "Lightning Distance"

Postby cellocgw » Wed Aug 01, 2018 6:24 pm UTC

Mikeski wrote:If you're in a situation like the comic, where the lightning bolt persists long enough to have an entire conversation about it, a call to your religious professional may be required, to see if there was an Armageddon scheduled.


That's a paranoid conclusion. I think it's much more likely that you've developed a highly efficient language which compresses hundreds of English words into a very specific 100-microsecond sound burst.
Or perhaps the two of you are spinning around a common center fast enough that you're communicating in relativistic time.
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Re: 2027: "Lightning Distance"

Postby Sableagle » Wed Aug 01, 2018 6:36 pm UTC

Heimhenge wrote:Important to note the sound wave from the lightning can be delayed, advanced, or refracted away. I've seen lightning that was definitely close enough to hear but remained silent (well, maybe not totally silent ... the rain can get kinda noisy). And then there's the reflected waves, smeared out into a rumble, that can also muddy your counting.

A bit simplistic but was fun to animate: http://sky-lights.org/2014/07/28/what-causes-thunder/


Oh, is that why there's no thunder in this video? I was wondering.
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Re: 2027: "Lightning Distance"

Postby pkcommando » Wed Aug 01, 2018 7:06 pm UTC

cellocgw wrote:
Mikeski wrote:If you're in a situation like the comic, where the lightning bolt persists long enough to have an entire conversation about it, a call to your religious professional may be required, to see if there was an Armageddon scheduled.


That's a paranoid conclusion. I think it's much more likely that you've developed a highly efficient language which compresses hundreds of English words into a very specific 100-microsecond sound burst.
Or perhaps the two of you are spinning around a common center fast enough that you're communicating in relativistic time.

Or you're living in a comic book.
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Re: 2027: "Lightning Distance"

Postby x7eggert » Wed Aug 01, 2018 9:04 pm UTC

Mikeski wrote:If you're in a situation like the comic, where the lightning bolt persists long enough to have an entire conversation about it, a call to your religious professional may be required, to see if there was an Armageddon scheduled.


You don't need to, as the bible says that nobody but the father knows the time.

Mathew 24:

Code: Select all

36 “But about that day or hour no one knows, not even the angels in heaven, nor the Son,[f] but only the Father. 37 As it was in the days of Noah, so it will be at the coming of the Son of Man. 38 For in the days before the flood, people were eating and drinking, marrying and giving in marriage, up to the day Noah entered the ark; 39 and they knew nothing about what would happen until the flood came and took them all away. That is how it will be at the coming of the Son of Man. 40 Two men will be in the field; one will be taken and the other left. 41 Two women will be grinding with a hand mill; one will be taken and the other left.

42 “Therefore keep watch, because you do not know on what day your Lord will come. 43 But understand this: If the owner of the house had known at what time of night the thief was coming, he would have kept watch and would not have let his house be broken into. 44 So you also must be ready, because the Son of Man will come at an hour when you do not expect him.

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Re: 2027: "Lightning Distance"

Postby Archgeek » Wed Aug 01, 2018 10:06 pm UTC

x7eggert wrote:
Mikeski wrote:If you're in a situation like the comic, where the lightning bolt persists long enough to have an entire conversation about it, a call to your religious professional may be required, to see if there was an Armageddon scheduled.


You don't need to, as the bible says that nobody but the father knows the time.

Mathew 24:

Code: Select all

36 “But about that day or hour no one knows, not even the angels in heaven, nor the Son,[f] but only the Father. 37 As it was in the days of Noah, so it will be at the coming of the Son of Man. 38 For in the days before the flood, people were eating and drinking, marrying and giving in marriage, up to the day Noah entered the ark; 39 and they knew nothing about what would happen until the flood came and took them all away. That is how it will be at the coming of the Son of Man. 40 Two men will be in the field; one will be taken and the other left. 41 Two women will be grinding with a hand mill; one will be taken and the other left.


Half? Blades, is Matt talking about Yeshua of Nazareth or dang ol' Thanos?!
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Re: 2027: "Lightning Distance"

Postby Mikeski » Wed Aug 01, 2018 10:26 pm UTC

Archgeek wrote:Half? Blades, is Matt talking about Yeshua of Nazareth or dang ol' Thanos?!

All you really know from reading that is that at least two will be taken, and at least two will be left behind; one of each sex in both cases.

In addition to knowing not the hour, you know not the grading curve.

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Re: 2027: "Lightning Distance"

Postby Soupspoon » Thu Aug 02, 2018 5:19 am UTC

Mikeski wrote:In addition to knowing not the hour, you know not the grading curve.

It's "most recent posters to the OTT", isn't it? Only I'm not sure which way the cut is, on that.

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Re: 2027: "Lightning Distance"

Postby Old Bruce » Thu Aug 02, 2018 5:25 am UTC

Soupspoon wrote:
Mikeski wrote:In addition to knowing not the hour, you know not the grading curve.

It's "most recent posters to the OTT", isn't it? Only I'm not sure which way the cut is, on that.

Surely it would be most relevant posts. [halo emoticon] [cloud emoticon] [harp emoticon]

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Re: 2027: "Lightning Distance"

Postby x7eggert » Thu Aug 02, 2018 8:02 am UTC

Mikeski wrote:
Archgeek wrote:Half? Blades, is Matt talking about Yeshua of Nazareth or dang ol' Thanos?!

All you really know from reading that is that at least two will be taken, and at least two will be left behind; one of each sex in both cases.

In addition to knowing not the hour, you know not the grading curve.


Daniel, Hiob and Noah are said to find grace, so it's three males.

I don't think it matters, though. You don't need to believe in God to start being a decent man, but if you are decent, you'll behave according to the bible anyway. Many people would be more decent if they behaved according to the sermon on the mount at least sometimes.

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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 9:44 am UTC

x7eggert wrote:... if you are decent, you'll behave according to the bible anyway.
What, all of it?!?
Many people would be more decent if they behaved according to the sermon on the mount at least sometimes.
Oh, that part.

Right.

Not that bit about setting your beard on fire and beating your own chest with it, then?
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Re: 2027: "Lightning Distance"

Postby Archgeek » Thu Aug 02, 2018 3:16 pm UTC

Sableagle wrote:
x7eggert wrote:... if you are decent, you'll behave according to the bible anyway.
What, all of it?!?
Many people would be more decent if they behaved according to the sermon on the mount at least sometimes.
Oh, that part.

Right.

Not that bit about setting your beard on fire and beating your own chest with it, then?

'The heck is that from, the book of Krog?
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Re: 2027: "Lightning Distance"

Postby grkvlt » Thu Aug 02, 2018 3:17 pm UTC

speising wrote:
jc wrote:And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

or rather, take the seconds times 3, which is closer to reality.


Interestingly, if you time the *duration of the thunder sound* as well, and multiply by 3, you get the *length of the lightning bolt* in km. This is because the sound is generated starting at the beginning of the bolt and then continuously as the flash is created along the length of an ionized channel in the air. The speed of the lightning is closer to c than the speed of sound, so can be ignored.
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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 3:39 pm UTC

grkvlt wrote:
speising wrote:
jc wrote:And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

or rather, take the seconds times 3, which is closer to reality.


Interestingly, if you time the *duration of the thunder sound* as well, and multiply by 3, you get the *length of the lightning bolt* in km. This is because the sound is generated starting at the beginning of the bolt and then continuously as the flash is created along the length of an ionized channel in the air. The speed of the lightning is closer to c than the speed of sound, so can be ignored.

Divide by 3? That's only the difference in distances between ends, though, isn't it? If the lightning's vertical and 20 km away, it being 5 km tall would only make the top 20000 - ( 20000 / cos ( tan-1 ( 5/20 ) ) ) further away, a whole 615 metres. Huh. Funnily enough, that's almost two seconds and multiplied by 3 that'd be about 5.

Same thing 1 km away, though, it'd be 1000 - ( 1000 / cos ( tan-1 ( 5/1 ) ) ) = 4099 m further away.
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Re: 2027: "Lightning Distance"

Postby hamjudo » Thu Aug 02, 2018 3:52 pm UTC

Sableagle wrote:
grkvlt wrote:
speising wrote:
jc wrote:And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

or rather, take the seconds times 3, which is closer to reality.


Interestingly, if you time the *duration of the thunder sound* as well, and multiply by 3, you get the *length of the lightning bolt* in km. This is because the sound is generated starting at the beginning of the bolt and then continuously as the flash is created along the length of an ionized channel in the air. The speed of the lightning is closer to c than the speed of sound, so can be ignored.

Divide by 3? That's only the difference in distances between ends, though, isn't it? If the lightning's vertical and 20 km away, it being 5 km tall would only make the top 20000 - ( 20000 / cos ( tan-1 ( 5/20 ) ) ) further away, a whole 615 metres. Huh. Funnily enough, that's almost two seconds and multiplied by 3 that'd be about 5.

Same thing 1 km away, though, it'd be 1000 - ( 1000 / cos ( tan-1 ( 5/1 ) ) ) = 4099 m further away.


Always assume that you are at the end of the lightning strike. It will make many many issues moot.

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Re: 2027: "Lightning Distance"

Postby Soupspoon » Thu Aug 02, 2018 3:56 pm UTC

hamjudo wrote:Always assume that you are at the end of the lightning strike. It will make many many issues moot.
Adopt a more positive attitude?

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Re: 2027: "Lightning Distance"

Postby ucim » Thu Aug 02, 2018 4:39 pm UTC

Soupspoon wrote:
hamjudo wrote:Always assume that you are at the end of the lightning strike. It will make many many issues moot.
Adopt a more positive attitude?
Just don't resist.

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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 5:07 pm UTC

Ohm y God. Okay, fine. Let's amp up the puns.
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Re: 2027: "Lightning Distance"

Postby orthogon » Thu Aug 02, 2018 5:39 pm UTC

Sableagle wrote:Ohm y God. Okay, fine. Let's amp up the puns.

Current puns? Mmmm...

Another thing everybody knows about lightning is that it doesn't strike twice in the same place. So that helps a bit by telling you where it isn't. (Actually I think we're back to the nonblack nonravens, aren't we?)
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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 5:45 pm UTC

orthogon wrote:
Sableagle wrote:Ohm y God. Okay, fine. Let's amp up the puns.

Current puns? Mmmm...

Another thing everybody knows about lightning is that it doesn't strike twice in the same place. So that helps a bit by telling you where it isn't. (Actually I think we're back to the nonblack nonravens, aren't we?)


Between the "giant ball rolling over the landscape" model for where it can hit and the videos of thunderstorms from space, that can't be true over any long time period. Maybe it's true within millisecond time frames.
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Re: 2027: "Lightning Distance"

Postby Soupspoon » Thu Aug 02, 2018 6:02 pm UTC

orthogon wrote:
Sableagle wrote:Ohm y God. Okay, fine. Let's amp up the puns.

Current puns? Mmmm...

Watt?

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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 6:07 pm UTC

ucim, would Joule like to take another shot at this?
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Re: 2027: "Lightning Distance"

Postby rmsgrey » Thu Aug 02, 2018 7:51 pm UTC

Sableagle wrote:
orthogon wrote:
Sableagle wrote:Ohm y God. Okay, fine. Let's amp up the puns.

Current puns? Mmmm...

Another thing everybody knows about lightning is that it doesn't strike twice in the same place. So that helps a bit by telling you where it isn't. (Actually I think we're back to the nonblack nonravens, aren't we?)


Between the "giant ball rolling over the landscape" model for where it can hit and the videos of thunderstorms from space, that can't be true over any long time period. Maybe it's true within millisecond time frames.


You forget that the entire planet is moving ~390 km every second (relative to the cosmic microwave background) so there's less than a minute before lightning can't hit in the same place again while also hitting somewhere on the Earth's surface...

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Re: 2027: "Lightning Distance"

Postby Sableagle » Thu Aug 02, 2018 8:49 pm UTC

It could hit another planet in the same place.
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Re: 2027: "Lightning Distance"

Postby ucim » Thu Aug 02, 2018 9:57 pm UTC

Sableagle wrote:ucim, would Joule like to take another shot at this?
I'm shocked you would ask.

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Re: 2027: "Lightning Distance"

Postby Reka » Thu Aug 02, 2018 10:34 pm UTC

C'mere, the lot of you. Stand still.

THWACK! THWACK THWACK THWACK THWACK THWACK! KER-THWACK!!!

That is all, carry on.

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Re: 2027: "Lightning Distance"

Postby GlassHouses » Thu Aug 02, 2018 10:37 pm UTC

Sableagle wrote:Alternatively, you could go with the helicopter pilot's approximation: if it's close enough for you to hear the thunder, it's close enough for you to get hit by the lightning.

Considering how loud helicopters are, being able to hear the thunder over that racket must mean being very close!

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Re: 2027: "Lightning Distance"

Postby gmalivuk » Thu Aug 02, 2018 11:01 pm UTC

grkvlt wrote:
speising wrote:
jc wrote:And then you multiply by 8/5 to get the distance in km, if you're among the 95% of the population who uses SI units.

or rather, take the seconds times 3, which is closer to reality.


Interestingly, if you time the *duration of the thunder sound* as well, and multiply by 3, you get the *length of the lightning bolt* in km. This is because the sound is generated starting at the beginning of the bolt and then continuously as the flash is created along the length of an ionized channel in the air. The speed of the lightning is closer to c than the speed of sound, so can be ignored.

If you divide by 3 instead of multiply, you would get the difference between the nearest point of the bolt and the farthest point (which is not the same as the length) if nothing between you and it serves to deflect or diffract or otherwise interfere with the sound waves.

Which is to say, that won't really happen, because a big part of the thunder sound you hear is echoes from things not directly in the path from you to the lightning.
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Re: 2027: "Lightning Distance"

Postby NotAllThere » Fri Aug 03, 2018 7:05 am UTC

Mikeski wrote:The important part of timing lightning is: "Did the lights in your house go out in time with the flash"?

Then you need to call the power company.
What do I do if my phone goes out in time with the flash?
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Re: 2027: "Lightning Distance"

Postby Sableagle » Fri Aug 03, 2018 9:53 am UTC

NotAllThere wrote:
Mikeski wrote:The important part of timing lightning is: "Did the lights in your house go out in time with the flash"?

Then you need to call the power company.
What do I do if my phone goes out in time with the flash?


Your phone line goes out? They'll probably notice and fix it.

Your mobile phone goes out? You'll probably topple and cark it.
Oh, Willie McBride, it was all done in vain.


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