Thursday, May 31, 2018

Basic Training - Magnetism

Deep inside the center of the earth, some 1800 miles down beneath the surface, is a 1500 mi. thick layer of liquid molten iron and nickel, which eddies and flows turbulently between the mantle and the solid central core. The flow of this material creates electrical currents which generate a magnetic field, which shields the planet from the solar wind, and without which the atmosphere would likely be rapidly stripped away, leaving the earth as barren and lifeless as Mars, the Moon, or parts of North Dakota. Coincidentally, that electrical field, having due to inescapable laws of physics a magnetic polarity, creates a field detectable upon the surface, that, while wandering slowly, is fairly constant over time (at least until periodic - in a geological timeframe - polarity reversals), and helpfully, that polarity is centered near enough on the actual rotational poles of the planet as to be directionally useful. It has been constant enough for several pivotal centuries to allow the brighter among humankind to note first its existence, its direction, and finally to deduce a fairly simple yet robust means for finding our way, by using a small piece of metal to align with the waves produced, point generally north, and thus develop the magnetic compass, useful for wayfinding since about the 11th century A.D. For reference, this was about the time a French-speaking lout named William from Normandy, no cheese-eating surrender monkey he, sailed to the south of Britanica, bringing with him horse cavalry unpossessed by the luckless army of King Harold, and thereby subjugated the Saxons of the kingdom, giving rise to modern England.

Neither William nor Harold possessed the magnetic compass, but the travels of Marco Polo to China retrieved the concept, the Renaissance spread it from Arabia to the Mediterranean and thence to all of Europe, soon remedying that lack even in far-off England, and the English soon sailed everywhere with one, eventually conquering and subjugating a great portion of the known world, until with their usual obtuseness and pedantry, they mismanaged most of their colonies in North America, leading inevitably to the colossally overweaning leviathan behemoth Deep State which we all loathe and despise in the present day.

So having covered the past up until now, let's talk about what the phenomenon of magnetism, and the invention of the magnetic compass means for you.

The slowly-wandering current-producing field of molten outer core I told you about creates a magnetic north pole. Its wanderings are intensively tracked and measured, getting more precise over time as both scientific curiosity, laboratory instrumentation, and the dependence of commerce and the vast wealth involved have cooperatively required such a keen interest in the otherwise unremarkable results of bubbling molten metal hundreds of miles beneath the frozen tundra and arctic seas of Canada.

Those measurements, coupled with the space-age ability to more precisely locate and compare the location of the magnetic north pole to the actual planetary North Pole have led to depictions of the variation to prevent someone from, for instance, crashing their ship into rocks, losing the cargo, and dumping millions of gallons of crude oil onto someone else's beach.

This rather important difference between magnetic north and actual north is called Magnetic Declination.

2015 map of magnetic declination worldwide.

This is all important to you, because it means your magnetic compass doesn't point at north on the map, and it doesn't point to the North Pole, ever, except occasionally along a very thin strip of the earth's surface, which also moves year by year.

Movement from 1590-1990 AD
Fortunately, it moves sloooooooooowly over time, and at a fairly constant rate, so you can apply a correction year to year, and get from compass to reality with second-grade math skills. Helpfully, for most of the inhabited surface of the planet, the correction necessary is seldom off from reality by more than 20 degrees or so, so the math is manageable.

So somewhere on your map, if it's not a touristy p.o.s. map, and definitely on both USGS and US/UK et al military maps, you'll find something in the margin like this:

Which shows you the difference between magnetic north (MN -where your compass is pointing), grid north (GN - which way the map is presenting the surface of a 3D sphere in a 2D representation), and true north (★-the actual direction in which the actual North Pole is rotating about dead-on beneath Polaris, the astronomically named "North Star").
I told you about that so we can get to the Compass next.


Anonymous said...

Fun and actually brief explanation of magnetic north that my Drill Instructors omitted. Actually I'd been backpacking before Boot Camp so perhaps just paid less attention to it.

Aesop said...

Two (there are more) of The Inviolable Rules Of Teaching

Assume everyone is as dumb as you once were.
Make the learning fun, and people won't notice the brainwork involved.

I note without irony that most of boot camp instructors could teach rings around most (like 90%) of my college professors, in either instructional venue, and that while I have no doubt the drill instructors and better platoon sergeants could instruct particle physics within about a week, I have sincere doubts that most college professors could grasp the rudiments of close order drill in less than thirteen weeks, let alone teach it.

Sgt. Zim wins again.

Anonymous said...

I learned such from my fighting instructor too. Teaching women self protection skills needed to be " light" most of them were scared to one level or another and so needed to laugh a bit.
My Senior was a three-tour Nam 0311, so was a multiple PhD

Badger said...

Nicely done. The animated declination GIF, by the way, falls into the "ok, that's honestly cool" category. Thanks for the effort in this whole endeavor - it's a good thing. (DoD are you listening?)

Sean said...

Could you test me here, and see if my skills need training? The diagram shows an eleven and a half degree Westerly, from grid to magnetic. So, using my old formula, to obtain the correct magnetic direction, such as it shows my objective to be 60, magnetic, I would add the eleven and a half degrees to 60 and call my magnetic direction at now 71 and a half degrees?

loren said...

" I have no doubt the drill instructors and better platoon sergeants could instruct particle physics within about a week"
Having a few semesters worth of said particle physics, they might be able to if they had a masters in mathematics first.
Intuitive logic and modern physics are not on the same page.

Anonymous said...

That’s correct. West is best, east is least was the mnemonic I was taught years ago in ground school. So add westerly and subtract easterly declination.

Aesop said...


You're missing the point: they can convey information, because they know how to teach, which requires something conveyed by no Master's program in existence, nor any training in mathematics beyond knowing it exists.

There are any number of people who are subject-matter experts in higher mathematics and hard sciences who can't convey what they understand even to their peers, let alone to a mildly interested student. Ask me how I know.

But someone who has virtually no understanding of a subject, but who knows how to convey information, simplify it, and amplify it can teach anything to anyone, even if they themselves are wholly ignorant of the arcana of the message.

We all have a bit of experience with this if you watch any TV that isn't sitcom: this is why documentaries hire actors to voice the dialogue, and the dialogue is written by people who may not even have college degrees, and are not (or very seldom, if ever) narrated nor authored by college professors. Teaching, like speaking well, is an art, not a science. Some people can do it naturally, others can learn, but the nine times out of ten, the pointiest-headed eggheads think they're too smart to learn such arcana, and consequently totally suck at conveying the information. As evidence for my case, you have every professor at every college in the world. Most of them should be fired outright, and most of the rest cut to half-pay until they can learn to teach their supposed subject. And most of what passes for training people to teach is wooly-headed education-school utter nonsense developed by the least-bright people in every university since forever. When you hire idiots, and reward idiocy, you get more idiots. That's American education for over a century, from K-Ph.D.

Big Bang Theory is funny because it's true: most highly intelligent and highly specialized science geeks are the most isolated and socially-inept dorks on the planet, since forever. Socrates wasn't killed because he was smart, but because he'd pissed off everyone in authority, and for his entire life, to the point that suicide or exile into the wilderness seemed reasonable to everyone else at the time. Provoking that kind of backlash against you is a special kind of social retardation, at the world-class level.

Physicists like Richard Feynman and Stephen Hawking are one in a million, and it's why mental mediocrities like Neil DeGrasse Tyson and bare electrical engineering graduate Bill Nye end up being spokespersons for fields far beyond their own depth.

It's like food; or diamonds.
We pay a rancher - a pure genius, who has to know arcane things about cows I couldn't care less about - for beef by the whole cow, and at nothing like the rate at which we compensate the guy who turns it into a hot steak on our plate, and the guy at the little end of the distribution chain doesn't need to know anything about the cow, or the subject of cows, except how to break it down and prepare and deliver it, so you can enjoy eating and digesting it.
Some guy working for slave wages may be carving raw diamonds out of rock under incredibly bad and dangerous conditions, and even the guy who runs the mine and is an engineering genius gets a relative pittance, compared to the guy who can take the merest scrap of their product and turn it into a bit of jewelry for a lady's finger.

If you can't deliver the goods to the consumer, you're not in the business, you're just a hoarder, eve if you're a brilliant and focused one.

Knowledge works exactly the same way.

loren said...

Well I do agree that an actor will read a script better than any professor and as such may be a better lecturer - not teacher. God knows I would have liked to have had better of both.
We once had a Chinese guy with a stutter teach a Thermodynamics course that was the hardest course in engineering. One day he evaporated an inch or so off his finger tips shorting out a laser power supply. Fucker really had a stutter then.
I will convey to you that interested STEM students will stick their hand up and ask "What about.........? or Why does.......? Actors will fail just about there. I'm guessing Nye and Tyson would too unless PC BS was allowed. From what I understand the military isn't too big on questions.
As to Hawking, he had one good theory a long, long time ago then more or less got sick. Feynman was a genius.

Aesop said...


1) You're getting ahead of the class. We'll go over this more in the Compass module.
2) No.
3) If you have your magnetic bearing to start, you have your magnetic bearing to walk.
4) If you meant to indicate the objective you seek is at 60° per the grid direction at the center of the map sheet, which you would determine best with a protractor, you would indeed add the 11½° to that grid bearing, and travel on an magnetic compass-indicated magnetic course of 71.5°.
5) This is all easier to grasp in meatspace when you're on the ground, with a compass out, and the map oriented towards reality.

Aesop said...

Most of teaching is in fact lecturing, going back a paltry few millennia of recorded history.
We have, for instance, no records of the blackboard diagram lessons or hands-on instruction of Moses or Jesus, nor even Buddha or Mohammed, AFAIK. No one seems to feel unduly constrained by that limitation.

Interested students of all types will stick their hands up. Even in the military.
It's not that the military isn't big on questions. Just the opposite.
I quote for Truth the Drill Instructor maxim:
"There are no stupid questions, only stupid people."
If you are asking a question not covered in the lecture, either it's a poor lecture, or you're off the map for that particular period of instruction.
In 95% of cases, in both college and the military (and damned near everywhere else, btw), you're asking because you weren't paying attention when the exact information you're asking about was covered sufficiently already. BTDT, got the t-shirts.

In the other 5%, you may have had a flash of inspiration, or found a flaw in the material, or the instructor. The odds respectively run to 0.001%, 1.999%, and 3%, in my personal experience both learning, teaching, or listening to others.
If, in the case of the 3% chance, they offer to address your inquiry after the class, look up what you're asking about to find what they don't know, or make appropriate clarifications on the spot, you're in good hands.
If they bluff, bluster, and/or attempt to bully you out of the way, RUN.
They're either idiots and know it, or they don't know they're idiots, and something bad will come to them in due course. Try not to be around when it happens if possible, particularly in a safety or military context; i.e. someone's going to die.

Hawking's book sales suggest he was rather more gifted at explaining pretty heavy theory than to be limited to one good idea.
And bear in mind Columbus only made one important voyage, Wilbur Wright only made one good launch, Edmund Hillary only climbed one good mountain, Chuck Yeager only made one good flight, and Neil Armstrong only took one small step. We don't commemorate the dozens to hundreds of other things they all did before and after, just the ones that move the flags farther beyond.

Humanity, and what it knows, moves outward one step at a time, because we only have two feet.

And if you can't tell somebody else how to get to that last step-off point, you may as well have never been there and done that.

Anonymous said...

It's also worth it to learn how to find Polaris with the stars.

Anonymous said...

"Socrates wasn't killed because he was smart, but because he'd pissed off everyone in authority, and for his entire life, to the point that suicide or exile into the wilderness seemed reasonable to everyone else at the time. Provoking that kind of backlash against you is a special kind of social retardation, at the world-class level."

Being the mentor of Critias, who murdured 5% of the Athenian population during the reign of the Thirty Tyrants, certainly didn't endear him to his fellow citizens. Aristophanes wrote a play (The Clouds) where a father sends his son off to study at Socrates' school, only to have his son turned against everything he was raised to believe. Sound familiar?

Aesop said...

@Anonymous 6:04
Stay with the class.
I'm posting lessons, not enyclopediae.

soapweed said...

Aesop: Thanks for your continued efforts on various topics. You take the raw diamond
to a nice finished product. The difference is that the diamond is worthless except for the industrials, whereas your thoughts are many times, of a lifesaving nature.
Much obliged.