FAQ_ _Exploration of the Earth's Magnetosphere

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Questions and answer--listed in the order received

Please note!

Listed below are questions submitted by users of "The Exploration of

the Earth's Magnetosphere" and the answers given to them. This is

just a selection--of the many questions that arrive, only a few are

listed. The ones included below are either of the sort that keeps

coming up again and again--the danger of solar eruptions, the reversal

of the Earth's magnetic field, etc.--or else the answers make a special

point, going into extra details which might interest other users.

Because this is a long list, it is divided into segments

Click here for a listing arranged by topic.

Items covered:

Reversals of the Earth's field (4 queries)1.

Can the Earth's field be used for spaceflight?2.

The Sun's magnetic poles3.Synchronous satellites4.

Magnetic field lines5.

Alternate theory of the Sun and solar wind 6.

The Geiger counter (4 queries)7.

Measuring the Earth's magnetic field 8.

The strength of the Earth's field 9.

Solar Eclipses10.

Magnetometer for Observing Magnetic Storms11.

Cosmic Rays12.

Magnetic Shielding13.Use of solar wind for space propulsion14.

A working model of the magnetosphere?15.

The Van Allen Belt16.

Magnets of different shapes17.

On building an electromagnet18.

Capturing the Energy of the Solar Wind 19.

About the Upcoming Solar Maximum20.

Lining-up of Planets21.

Radiation Hazards to Air Crews22.

"Exploration of the Earth's Magnetosphere" http://www-spof.gsfc.nasa.gov/Education/FAQs

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The Ozone Hole and the Magnetic Field 23.

How are Ions produced?24.

About the "Starfish" artificial radiation belt25.

How do Magnetic Reversals affect Animal Migrations?26.

Which is the "True" North Magnetic Pole?27.

Electric and Magnetic Energy28.

Any connection between Solar Wind and Solar Flares?29.

Ozone and the Magnetic Field 30.

What if the Radiation Belt Reached the Ground... ?31.

Free Energy from the Earth's Magnetic Field?32.

Relativity33.

What is a "REM"?34.

What exactly does "Radiation" Mean?35.

Can anything solid be carried by the solar wind?36.

Dimensions of the Magnetosphere (2 related questions)37.

Skywriting by Aurora38.

Capturing the energy of solar wind ions39.

Radio Propagation40.

Radiation Belts and Manned Space Flight41.Magnetc shielding against neutral matter?42.

When and where can I see "Northern Lights"?43.

Universal Time and Magnetic Local Time44.

Does the magnetosphere affect weather?45.

"Importance of auroras to society"46.

Magnetic storms and headaches47.

Apollo Astronauts and radiation48.

What materials does a magnet pull?49.

Experimental simulation of the polar aurora50.

Cosmic ray research using balloons51.Magnetic health products52.

Geiger counters for locating lost objects53.

Magnetic effects from other planets54.

Blocking of the Solar Wind by our Moon?55.

Fry or Freeze... ?56.

The Speed of the Solar Wind 57.

What is "Radiation"?58.

How does one Contain a Plasma?59.

Soviet Nuclear Explosions in Space60.

Can Polar Aurora be seen in Atlanta, Georgia?61.

Why no aurora at the magnetic poles?62.

When and how were positive ions discovered?63.

Did astronauts use articifial magnetic shields"?64.

Harvesting electrons from power lines?65.

How can the intensely hot Sun be magnetic?66.

What are "geomagnetic conjugate points"?67.

What is the smallest magnet possible?68.

Can plasma physics explain ball lightning?69.

Harnessing the Energy of the Aurora?70.


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Radiation Belt and Brazil71.

Risks from stormy "Space Weather"72.

Man-made triggering of radio emissions73.

Does our magnetic field stop the atmosphere from getting blown

away?

74.

Radius of particle gyration75.

Are electric storms an "electromagnetic" phenomenon?76.

How can steady magnetic fields induce electric currents?77.There are electromagnetic waves all around us!78.

Best orbit for a Space Station79.

Is space debris electrically charged?80.

Magnetic induction by the Magnetosphere81.

Questions about the Solar Corona:

(1) Why don't its particles separate by weight?

(2) What accelerates the solar wind?

82.

Why has the aurora been so frequent lately?83.

Was the magnetosphere involved in the hole in the ozone layer?84.

Who Discovered Sunspots?85.

"Soda-Bottle Magnetometer"86.

Magnetism and Weather 87.

Is the Polar Cusp visible to the Eye?88.

Effects of Radiation beyond the Van Allen Belts89.

Deflection of a beam of Electrons in the Earth's Field 90.

Space Tether 91.

Does the Earth's magnetic field rotate?92.

Dynamo currents at Jupiter's moons93.

A Russian space tether experiment?94.

How come a magnetic field can block particle radiation but not light?95.

What is a "magnetic moment"?96.

Is fire a plasma?97.

Do interplanetary field lines guide the solar wind back?98.

Magnetic connections between planets and the Sun99.

The solar wind and solar escape velocity100.

Space tether to remove trapped radiation?101.

Electromagnetic Waves and Electromagnetic Induction102.

Solar wind effects on our lives103.

Weaker global magnetic field--higher cosmic ray dosage?104.

Sound waves on the Sun?105.

Mapping the magnetosphere using a surface network?106. History of Cosmic ray Research107.

What causes sunspots108.

Why does Plasma Follow Field Lines?109.

A solar wind contribution to global warming?110.

Waves in the Magnetosphere111.

What are "frozen" magnetic field lines?112.

Why doesn't magnetism affect electro-magnetic waves?113.

Eddy Currents114.

What is the Radius of the Sun's magnetosphere?115.

Project to show that Iron rusts faster in Fresh Water 116.


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Fluorescent lightbulbs117.

More about the Year 2012118.

Can Space Plasma help Spacecraft Propulsion?119.

When is Earth an Insulator and when a Conductor?120.

Can upper atmosphere atoms join solar wind?121.

"Radiation Remediation"?122.

Who invented AC?123.

Geiger Counters (1)

(Followed by Geiger Counters (2)

124.

Fluorescent tubes lighting up near high voltage125.

Earth's field--Magnetic or Electromagnetic?126.

How to test a Geiger counter 127.

Gamma ray bursts128.

Magnetic effects of our galaxy129.

How does electromagnetic induction occur?130.

Magnetic field of the Sun131.

Flux Transfer Events (FTEs)132.

Building a Terrella experiment like Birkeland's133.

Electric field due to electromagnetic induction134.

If you have a relevant question of your own, you can send it to

education("at" symbol)phy6.org

Before you do, though, please read the instructions

Reversals of the Earth's Magnetic Field

(4 queries)

Note added July 2001: Since these replies were written, I produced a web

site "The Great Magnet, the Earth". It discusses reverals in its section

"Magnetic Reversals and Moving Continents".

-----------

(1) I need to know as much as possible about the reversal of the magneticfield:

how it was noticed

who discovered the reversal

how long ago did it reverse

how many times did it reverse

more information about the radiation from the sun if the magnetic field

reverses.

Reply

ABOUT GEOMAGNETIC REVERSALS: This is a huge subject and I


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cannot do quick justice to it: look up in the index volume of the Britannica

under: Geomagnetism, Plate tectonics, Reversals of the Earth's magnetic

field.

HOW IT WAS NOTICED: When lava pours from a volcano, it solidifies to

a black rock called basalt. Basalt is slightly magnetic, and it takes on the

direction of the surrounding magnetic field at the time it solidifies. Scientists

examined lavas for their magnetism early in this century (I believe) to see

how consistent the direction of ancient magnetic fields was with the directionwe observe now (would compasses point in the same direction?). The

directions generally agreed, but there existed reversals of directions which

suggested that there were times in the past when the poles were roughly

interchanged.

No one knew what to make of it. Some suggested "polar wandering", that the

whole surface of the Earth slid around the interior like a loose shell.

WHO DISCOVERED:Bernard Brunhes, in 1909.

But a big change happened in 1963. People noted that while rocks on Earthwere magnetized in a disordered way, the sea bottom was magnetized in long

strips. Larry Morley (whose article was regarded so speculative that journals

would not publish it) and then Matthews and Vine (who managed to publish)

suggested that molten rock was spreading out like a conveyer belt from

volcanic cracks in the middle of the ocean floor, e.g. the one in the middle of

the Atlantic (Azores islands sit on it). Or rather like 2 belts, one moving

towards Europe, one towards America, carrying on them the continental

plates, so that Europe and America gradually drift apart. As each belt comes

out of the crack, its lava solidifes to basalt, causing it to become magnetized,

and when the field reverses, its magnetization reverses too. So the bottom of

the ocean records the field like the tape of a tape recorder, containing perhaps 50 million years of record.

HOW LONG AGO: about 700,000 years, according to the "tape recorder"

HOW MANY TIMES: Many, about half a million years apart on the

average.

RADIATION FROM THE SUN: Sunlight of course is undisturbed.

High-energy protons from the Sun are usually diverted by the magnetic field.

During the reversal the field probably does not disappear, but becomes

complex and weaker, and protons can more easily reach the atmosphere, asthey do now within 1000 miles or so of the magnetic pole. On the ground it

makes no difference because the thick atmosphere shields us very well, and

none of the protons penetrates far into it.

David P. Stern

Question #1-B


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Reversal of magnetosphere

We have been studying the magnetosphere and the Van Allen radiation belts

in a high school physical science class. It has been brought to our attention

that the magnetic poles of the earth reverse on an average of about every

500,000 years. The last change was about 700,000 years ago, so it would

appear that we are long overdue.

What are the implications of this? How significant would the fluctuation of

the magnetic field during such a change be on our protection from solar

wind?

Ricky

Reply

Dear Ricky

Only yesterday a similar question was submitted, so as a shortcut a copy of it

[next item below] and its answer are attached below.

Some people worry that during magnetic reversals the Earth would receive a

higher dosage of high-energy ions and electrons ("radiation" in common

terms), which might affect us and any living creatures on Earth. This is not

so. Even today, the magnetic shield is not effective near the magnetic poles,

yet the radiation received there on the ground is only slightly higher than

anywhere else. The reason is that our main shield against such particles is not

the magnetic field of the Earth but the atmosphere, equivalent to some 10

feet of concrete.

In any case, during reversal the magnetic field does not go away, it only getsweaker and develops several more magnetic poles, at unpredictable

locations.

Question #1-C

Could you tell me when the earth's magnetic poles will change, and what will

happen when it does? Will it happen fast (seconds) or slowly? Thank you!

Sarah

Reply

Dear Sarah

No one knows when the next field reversal will occur: in the past, they

have occured on the average about once in 700,000 years. The change,

whenever it occurs, will be gradual and the field will not drop to zero in

between--doing so would mean that the magnetic energy of the Earth was

somehow converted or dissipated, and all processes we know for this tend to

run on scales of thousands of year, if not more.


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Right now the main (dipole) field is getting weaker at a rate of about 7%

per century, and if you draw a straight line through the points you find it

reversing between 1000 and 2000 years from now. It might happen, though

the trend may also change before then. But as explained elsewhere, even if a

reversal occurs, the field does not disappear during the time of polarity

change, it just gets more complex and weaker.

The polar field of the Sun seems to reverse every 11 years or so, taking about

a year or more. But the Sun's magnetism is different, it has foci right on thesurface, in sunspots.

Hope this answers it.

David Stern

Question #1-D

Earth's magnetic field weakening--leading to a pole shift?

I am just a tax paying citizen, interested in astromony all of my life. I am

very interested in the physics of our earth which I believe is related to

astronomy as it is our home and a part of this solar system.

My question is: Is the earths magnetic field weakening, heading to zero

point? With this, is the base pulse frequency of the earth speeding up causing

the magnetic fields to fluctuate so that it interferes with the pilots

navigational equipment, so that the navigational charts have to be redrawn

periodically and the air strips renumbered? Are the magnetic poles

fluctuating? My experience is that they are. I have a quality, liquid filled

compass secured to my desk. It has been very still now for the past month but the six weeks or so prior to that, there were consistant fluctuations in its

direction, up to as much as 2 1/2 degrees, always to the west.

My understanding is: I have seen photographs of the sun taken from

satellites, showing the sun going through major activity. Repolarizing itself?

Causing the earth to repolarize itself? Going through a natural cycle as it has

many times in the past with pole shifts? On a scale from 1 to 10, with 1 being

the weakest and 10 the strongest, 2,000 years ago it was a 10, today it is a 1.

Is it heading for a zero point when a pole shift will occure? The closer it gets

to the zero point, the more fluctuations will occur?

Are the change in the magnetic frequencies causing at times a confusion in

migratory animals? Causing cells to mutate, changing the DNA pattern

within the cell? Causing certain strains of bacteria such as staph infections to

become resistant to our antibiotics and causing new viruses to appear that we

have never seen before, being able to survive in a new magnetic frequency?

I believe these are very facinating times in which we live. The science of all

of this intrigues me to no end. I have some taped interviews of scientists and

geologists relating to this subject and I read all that I can get my hands on, on


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the subject also. Your straightforward comments and answers will be most

welcomed to help me to understand more, what is taking place. Thank you so

very much.

Michael

Reply

Dear Michael

Questions on reversals regularly arrive at this desk, and some others are

listed above. And by the way, the source of the magnetic field is not any

polarization (at the Sun or Earth) but electric currents, flowing below the

visible surface of the Earth or Sun. In "The Great Magnet, the Earth" you

will find a great deal of material on the magnetic fields of Earth and Sun and

the way they probably arise.

Now to your questions.

Is the Earth's field getting weaker? Yes and no. That field is often viewed as being a two-pole ("dipole") structure similar to that of a small bar-magnet at

the center of the Earth, inclined by about 11 degrees to the rotation axis of

the Earth, so that the magnetic poles are not the same as the geographic

ones. But the actual situation is more complicated, and magnetic charts note

the fact by mapping deviations between magnetic north and the direction to

the magnetic pole, which fit no simple pattern.

Why? Because the magnetic field is actually more complicated, and it

contains additional fields, of more complex nature. All this originates in the

Earth's core, about half the radius of the Earth. If we could go to the surface

of the core, all the complicated parts would be much bigger. But theyweaken more rapidly with distance, so at the surface of the Earth they are

already quite weak, while the "dipole" part stands out more (in addition of

actually BEING the biggest chunk of the field).

Are you still with me?

The magnetic field of the Earth changes all the time, and yes, magnetic

charts have to be redrawn from time to time (this was first found in 1641, by

an Englishman named Gellibrand). And yes, in the century and a half since

the first careful mapping of the Earth's field, the dipole has become weaker

by about 8% (the rate may have speeded up in 1970). If you draw a straightline through the points, you will find that perhaps 1200 years from now, the

line goes through zero.

Extending straight lines too far beyond the present, however, is risky

business, as noted by no less a scientific authority than Mark Twain. In "Life

on the Mississippi" Twain noted that the Mississippi river was getting

progressively shorter (mainly by floods--and by people--creating shortcuts

through bends in the river) and he wrote:

"Now, if I wanted to be one of those scientific people, and "let on" to


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prove what had occured in the remote past by what had occured in a

given time in the recent past, or what will occur in the far future by

what has occured in late years, what an opportunity is here! ... Please

observe:

In the space of one hundred and seventy six years the lower

Mississippi has shortened itself two hundred and forty-two miles. That

is an average over a mile and a third per year. Therefore, any calm

person, who is not blind or idiotic, can see that in the lower OoliticSilurian Period, just a million years ago next November, the lower

Mississippi was upward of one million three hundred thousand miles

long, and stuck out over the Gulf of Mexico like a fishing rod. And by

the same token any person can see that seven hundred and forty years

from now the lower Mississippi will be only a mile and three quarters

long, and Cairo and New Orleans will have joined their streets

together, and will be plodding comfortably along under a single

mayor... There is something fascinating about science. One gets

such wholesale returns of conjecture out of such a triflinginvestment in fact."

It is not impossible that the magnetic field will go through zero 1200 years

from now, but (judging by the past record of reversals) not likely. In any

case, the field is not going away: a "flux preservation theorem" suggests this

is not happening (at least not on the relatively fast time scale of observed

variations of the field; see here). In agreement with that theorem, one finds

that while the dipole field is getting weaker, the complicated parts are getting

stronger. That's why I wrote "yes and no." During a reversal the two-pole

(dipole) component of the field (which now dominates it) may go through

zero, but the complex parts of the field will be relatively high, and because of

them, while the overall field will be weaker, it won't vanish.

I don't know about migrating animals (they may have magnetic organs, sort

of built-in compasses), but there seem to exist no magnetic effects on DNA,

resistance to antibiotics and so on; those changes seem more related to

chemistry.

Finally, be cautious with compass readings in your house. Houses do contain

electric currents and machinery, and these may affect the readings of a

magnetic compass. On NASA's satellites the magnetic sensor usually sits at

the end of a long boom, to keep it away from interfering electric currents in

the satellite's circuits.

Keep up your interest in science!

David

Back to the main list

2. Can the Earth's field be used for spaceflight?

Dear Mr. Stern:


9 7/4/2013



I am an Industrial Technology teacher at a middle school and one of

my students is dreaming of a space propulsion system based on

magnetic repulsion of the earth's magnetic field. Could you possibly

squeeze in a moment for us and provide some information on the

strength of this field and how it has been measured and maybe a

relative comparison? Tyson, my student, is really excited about the

Internet and will be enthralled to have an answer from a NASA

scientist. Perhaps you could steer him to other references as I certainly

will explain to him how busy a schedule you must have. Thank you.

Reply

I am afraid it won't work. First of all, the magnetic field is very weak.

Compared to fields in electric machinery, where appreciable forces are

exerted, it is a few thousand times weaker.

But there is a more fundamental reason. Magnetic poles always come

in pairs, equal and opposite: if a field attracts an N pole, it repels the

attached S pole. Similarly, if we generate the field by a current in a

loop of wire --say, shaped like a rectangle--for each side in which the

current flows in one direction, there exists a side where it flows in the

opposite direction, and the magnetic field exerts opposite forces of

equal strength on the two sides.

From the preceding one would guess that magnetic forces always

cancel, and no net force is exerted. So how come magnets are

attracted to each other, or pins to a magnet (same thing, really, since

each pin in the magnetic field turns into a small magnet)?

The answer is that the forces on the N and S poles (or on the opposing

currents) are not exactly equal, if one pole, or one wire, is closer to thesource of the field than the other. This can be put into a mathematical

formulation and the bottom line is that a suitably oriented magnet may

be attracted by a magnetic field, moving towards the greatest strength

of that field. But the force is proportional to the rate at which the field

changes with distance, which in the case of the Earth, is very small.

The idea of magnetism as anti-gravity has come up before. Your

student may look up "Gulliver's Travels" by Swift, where in the third

voyage, in a spoof on science and learned societies, Gulliver arrives at

an island floating in the air, held there by the repulsion of a large

magnet. Swift even gives an explanation, except it's all gibberishgobbledygook, as befits a book of satire. (I won't cite here the name of

Swift's island, since too many people in Texas speak Spanish!)

David Stern


3. The Sun's Magnetic Poles


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opposite to that of the Earth.

For more on the Sun, see:

http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html

Kenneth Philips, "A Guide to the Sun", Cambridge U. books,

1992 (paperback '95).

Yours,

David Stern


4 Synchronous Satellites

Dear Dr. Stern:

I have been told, and read, that in order for a satellite to remain in afixed position relative to the earth, it must be in a synchronous orbit,

and that this type of orbit is best for communication purposes. All of

the other orbits I have read about are used by satellites with goals

other than communication. Satellites in orbits other than synchronous

are not fixed in position relative to the earth.

This being the case, it seems to me that all satellite dishes for reception

of TV signals would face the equator - south east, south west, or

somewhere between. My observation of satellite dishes does not seem

to support this concept. Many dishes do have a southerly inclination,

but others do not. Further, here, where we are close to the equator, itseems to me that in order to focus on a satellite, the dish should be

aimed high - higher, at least, than one located in the USA or Canada

where the angle between the earth and the satellite would be smaller

than here in Barbados. Many dishes here seem to follow a line of sight

that is barely above the horizon.

So, my question - are all communication satellites in fixed orbits above

the equator, and if so, why don't all reception dishes face the same

way?

As I said at the outset, I know that I am being brash in writing you, and

I would appreciate your indulgence. Over the past year or so, I have

asked at least a half dozen engineers for an explanation, and received

little more than a blank stare in response. Access to other resources

here is not always easy. If you are unable to take the time for an

explanation, perhaps you would direct me to a source that could

satisfy my curiosity.

If you do reply, please bear in mind that I am an accountant, not an

astronomer.


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Reply

I am very glad to hear from you, to find someone as far away as

Barbados interested in satellites, but I have no good answer to your

question. It is absolutely true that all commercial communication

satellites orbit above the equator, at a distance of 6.6 Earth radii, with

a 24-hour period, which keeps them above the same station. You know

probably that the space shuttle and other low-altitude spacecraft

complete one orbit in about 90 minutes: the further out you go, the

longer it takes, until you reach the moon, which takes one month. So it

stands to reason that somewhere in that range the orbital period is

exactly 24 hours. If a 24 hour orbit is inclined to the equator, the

satellite does not stay above the same spot but wanders back and

forth: so it must be an equatorial orbit. Only then can the antenna on

the ground be fixed in one position.

It is true, however, that not all satellites tracked from Barbados are at

the longitude of the island. To receive phone calls from Europe, say, it

could be that a satellite is tracked which is orbiting at the longitude of

Europe, and then the dish should point towards the southeast.

I do not know how you reached my name; maybe you were directed

by a search engine to the file.

http://www.phy6.org/Education/wsynch.html

I hope you are aware that this is only one part in a much larger

exposition, the Exploration of the Earth's Magnetosphere, dealing with

the Earth's magnetic environment, with its home page at

http://www.phy6.org/Education/Intro.html

You might look it up. Also try:

http://www.phy6.org/Education/wlagran.html

dealing with satellites keeping a fixed position (or staying close to one)

relative to the Earth in its orbit around the Sun.

David P. Stern


5. Magnetic Field Lines

Mr. Stern,

I am enjoying your presentation on magnetospheres very much and I

am finding it most interesting and informative. However, I have one

question that I have not found an answer to yet.:


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If the earth's magnetic lines of force are in fact "lines" upon which

electrons and protons can collect like "beads on a wire", what is the

spacing between these lines say, at the altitude of the recent Tethered

Satellite experiment?

Some co-workers and myself have had a rather heated discussion on

this matter (i.e. whether the magnetic lines are "lines" or a "field"). We

would be most greatful if you would enlighten us about these magnetic

lines of force around our planet just a little more than you have in your presentation on the Goddard Home Page on the WEB.

Reply

Be very careful here! Magnetic field--space modified by magnetic

forces, so to speak--is one thing, and magnetic field lines are

something else again. They are a mathematical description of that

field, no more tangible than lines of latitude and longitude which

describe the surface of the Earth. One never asks how close THOSE

lines are; you can draw any number of them, depends how tightly you

are willing to space them.

Magnetic field lines are defined as lines that point everywhere along

the magnetic force (in a fluid, a complete analogy is given by flow

lines or "streamlines"). They can be described by formulas, in terms of

quantities known as Euler potentials or Clebsch functions.

But there also exist intuitive properties: particles threaded by a

common field line, tend to share that field line later on as well. Say we

have 10 ions numbered 1... 10 sitting on a common spot on the Sun,

and therefore sharing there a field line, and destined to come out in the

solar wind one day apart. The Sun rotates, so make a drawing with acircle representing the Sun and 9 radial lines coming out about 15

degrees apart. After 10 days, particle #1 is 2.5 inches along the first

line, particle #2 2.25 inches on the 2nd one, and so on, down to

particle #10 still on the surface: the line conecting the particles is a

spiral, so we expect interplanetary field lines to have a spiral shape,

and we derived this from intuitive concepts alone (though the same

thing can be derived from formulas).

The details of this excercise are described in http://www.phy6.org

/stargaze/Simfproj.htm.

The spacing between field lines is not meaningful (though someengineers speak of "density of magnetic field lines" to describe a

quantity commonly known as "flux density.") Suppose you draw two

field lines of the Earth, reaching Earth 1 meter or 1 foot apart. Each

can have electrons or ions trapped around it. The meaningful question

is what is the radius of the circle these electrons or ions describe

around their guiding line, and that depends on their energy, and how

strong the field is (the circle gets larger in the weak fields far from

Earth), but it is generally much more than 1 foot or 1 meter. No

problem: densities are so low that such ions or electrons rarely collide,


29 7/4/2013



and their orbits can easily overlap. The radius of gyration of auroral

electrons can be 100 meters, which is why auroral "curtains"are so

thin. On the other hand, solar wind ions entering near the "nose" of the

magnetosphere have radii of the order of 500 kilometers, or (say) 350

miles, because the field there is much weaker, and that is therefore the

order of the expected thickness of the magnetopause, the boundary

between the solar wind and the magnetosphere.

David P. Stern


6. The Solar Wind

To David P. Stern:

Hello David, I liked the WWW article on The Solar Wind-History. In

the article it said:

"Not everyone accepted Parker's theory of the solar wind

when it was first published in 1958, and it was debated

until observations confirmed it."

Have you ever heard of the book OAHSPE by John Ballou

Newbrough copyright 1882? Oahspe means Earth, Sky, and Spirit.

Oahspe contains much scientific information that was discovered

many years later, such as the earth's magnetosphere, Van Allen

Radiation Belts, the SOLAR WIND, the origin of stars in nebula, the

configuration of galaxies, the beginning substance of life(DNA) in

nebula, the cycle and age of galaxies and the stars they contain,

interstellar and intergalactic Unseen matter(Dark matter). Oahspe says

the Sun has a vortex that streches throughout the solar system.

Scientist have some knowledge of the Sun's vortex, they call it the

"Solar Wind'. .... (most of the letter omitted)

Tell me what you think about it. Please send me a reply email. Hope to

hear from you soon.

Reply

I am sorry to have to disagree with you, but just coming out with astatement which is later verified is not a prediction, unless it is

supported by cogent arguments, which distinguish it from similar

predictions which were not verified. That's the essence of the scientific

method: what we believe to be true is based on a tight interlocking

web of observed evidence. The first evidence for the solar wind came

from comet tails, whose behavior had been explained by sunlight

pressure: it took a lot of physics to understand why this process

worked on dust tails, but not on ion tails. Parker's theory was based on

the high temperature of the corona, discovered in 1939 or so, and

again involved some intricate physics.


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The solar wind, by the way, is not a spiral: it flows straight out. Only

the Sun's magnetic field lines are spiral, because the sun rotates: they

tend to act like continuous strings, and since their "roots" rotate with

the Sun, they get twisted into spirals.

David Stern


7. The Geiger Counter

7a. Explaining the Geiger Counter

Hi, I am a 10th grader ...I came across a web site ... in my search for

how a geiger counter meter works. I was hoping you could give me a

relatively simple yet good explanation of how it works (preferably,

really simple). I'd appreciate it very much.

Thank you.

Reply

And I thought "Exploration" did give a simple explanation!

Imagine a fast ion or electron going through the tube. On its way it hits

atoms of the gas in the tube and ionizes them--knocks off electrons

and leaves positive ions. Usually, such electrons recombine soon. But

if there is a voltage difference (electric field) in the tube, before they

can do so, the electrons will start moving towards the positive wire and

the ions towards the negative walls.

As they move, they gain energy. This is particularly true near the wire,

where the electric field is concentrated and its force is strong. (One

can draw electrical field lines just like magnetic field lines, and near

the wire they bunch together, like magnetic field lines near the poles of

a magnet.)

If the energy gained by the average electron is enough to knock out

additional electrons from atoms of the gas with which it collides, the

number of electrons will multiply. As the electrons move towards the

wire and the field gets strong, this process grows quickly: one electronfrees up two, two release four, and by the time the wire is reached,

many more electrons arrive than were released by the initiating

particle, enough to draw a measurable current and create a signal in

the circuitry attached to the counter.

There is much more, of course, e.g. ultraviolet light which spreads the

process away from the wire as well, which could cause the current to

continue without stopping even after all the initial electrons (and the

additional electrons caused by them) have reached the wire. Special


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gas filling takes care of that.

The counter is usually charged by just a trickle of current from a high

voltage source, so that the current taken by the discharge is easily

measured. If too many particles pass through the tube, too much

current is drawn, the voltage drops and the discharges get smaller, until

the electronic circuits supposed to count them don't do so any more. I

think that's what happened on Explorer 1.

David Stern

7b. Building a Geiger Counter

Hello!

I found your web-site in the internet. But I have still two questions.

1. Which gas is suitable?

2. Which pressure is in the metal tube(vacuum?)?

Please can yuo send me a wiring diagram from a geiger counter.

Best regards

Matthias

Reply

Dear Matthias

I did my thesis work with Geiger counters, but that was 40 years ago

and my memory of that time is sketchy. If you have a local universitywith a physics department, it (or at the very least, its library) could

provide you with much better and much more up-to-date information.

Here is what I remember

You should understand, of course, that if the Geiger counter is a

metal tube, the end plugs must be glass, with a tight metal-

to-glass seal, because the central wire must be insulated from

the tube. Or else, the whole thing is inside glass, and the tube

nowhere touches the wire.

1.

When a particle passes inside, it creates ions and initiates a

discharge. But you don't want the discharge to get too big. As

noted, the counter has two main parts, insulated from each

other--a cylindrical metal tube and a thin wire through its

middle. The two act like a small capacitor, a device that holds an

electric charge when a voltage exists between its two parts. For

example, the tube may be connected to the ground (voltage

zero) and the wire may be charged through a lerge resistor

(which only allows a small trickle of current to flow) to some

high positive voltage, say 1000 volts; the exact number depends

on the design of the counter.

2.


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Now when the counter discharges, the electric charge from the

wire jumps over to the tube, and the voltage between the two

momentarily drops down--not to zero (the discharge is never

complete) but by a few hundred volts. A small additional

capacitor can transmit that jump to an external circuit, which

registers a "count." Afterwards the counter is "dead"

(insensitive) for a small fraction of a second, while the

capacitance between the wire and cylinder refills to its operating

voltage of 1000 volts.

3.

The trick with the counter, if I remember, was for it not to go

into a continuous discharge. The filling, at a pressure of a few

tens of milibars, was either alcohol vapor or halogen. Alcohol

stopped the discharge by itself, but was gradually broken up by

the discharges, so that the counters had a certain lifetime.

Halogen--I don't remember what it was--chlorine?-- lasted

longer but needed an external electric circuit to give it a large

negative pulse and shut it off, after each discharge. In either

case, the voltage was critical--too big, it went into a continuous

discharge, too small, the pulses were small, too, in what isknown as the "proportional counter" regime. Today many

people prefer proportional counters, since the electronics can

amplify the pulses very well. But 40 years ago it was good to

have a detector whose output pulse was big enough without any

amplification. The pulse was carried out through a small

capacitor, which let the pulses through to whatever counting

circuit was used, but kept out the high voltage.

4.

I hope all this is useful. Sometimes simple questions lead to

complicated answers!

Yours

David P. Stern

7c. Who was Hans Geiger?

Hi

My name is Matt and I am a High School student in Corona, CA. I was

recently assigned to do a report on a scientist. I found Hans Geiger

interesting, and I picked my topic to be about his work.

Reply

Hans Geiger was a young German assistant to Ernest Rutherford

(about whom you might have found and written much more!).

Together with Ernest Marsden he helped Rutherford in his famous

experiment which established the existence of a heavy, positive

nucleus at the center of each atom. That was in Manchester, in 1909,

and you can read about it in "Giant of the Atom," a biography of

Rutherford for young readers by Robin McKown, first published in


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1962 (your library may have it).

You might also find some about his work in the beginning chapters of

The Making of the Atomic Bomb" by Richard Rhodes and "From

X-rays to Quarks" by Emilio Segre (look him up in the indexes).

Later he devised the "Geiger counter" instrument and helped deduce

laws of radioactive decay.

#7d Questions connected to the Geiger Counter

Hello Dr. Stern,

Please answer to my following questions. My father couldn't help

me. I am very happy now to know you.

The initial electrons create an avalanche in Geiger Counter. I

don't want to disturb the avalanche. Will this avalanche remain

even when the initial electrons are stopped, providing enough

atoms are existing in the tube?

1.

Geiger counter need over 1000 volts. How is it possible to

create this high voltage in a small handy counter. What is

actually the electrical consumption of these counters?

2.

I assume the avalanche is a mixture of electrons and ions.

Using two different metals, installed in the Geiger Tube, can I

separate the electrons and ions out of each other? In other words

absorbing two opposite charges using two different materials.

How sounds it if I use a magnet for separation and direct the

opposite charges to those different metals?

3.

How many electrons or ions roughly create an avalanche?4.

If "Z" is the number of electrons in an avalanche then I can

say there is a negative charge of Z x 1.602 x 10 –19 which I can

use it as a potential energy(?)

5.

If in vacuum the alpha particles strike a metal, this metal gets

positively charged?

6.

Your answers will be greatly appreciated. These questions bother me every night when I lie in bed.

Reply

Your message was very much appreciated. You must be fairly

young, or else you might have asked not your father but your physics

teacher or professor. Yet what you ask are demonstrate thought and

understanding). I hope you will continue to pursue your science


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interests, because you seem to have what it takes. I will try to answer,

but please remember, I am no expert.

You can assume enough atoms exist in the tube--after all,

their number does not change. As some get electrons separated

to become ions, other ions recombine.

The avalanche is complicated. It occurs mainly near the

central wire, where the electric force is concentrated in a narrowregion and is therefore strong (similarly, if a metal object has

sharp spikes and you charge it electrically, the electric force is

strongest near the spikes, and that's where sparks are most

likely). The process also involves ultra-violet emissions, and

these can make create a "continuous discharge," for a long time.

You of course do not want that to happen.

All sorts of effects can be used to end the discharge. If the

capacitor which stores the high voltage is only filled by a small

trickle (through a big resistor), the discharge may drain it and

lower its voltage, to where the avalanche stops. Or else, anelectric circuit can sense the discharge and forcibly lower the

voltage. This has the same effect, but produces less "dead time,"

during which the counter waits for the capacitor to fill up again

and is therefore temporarily inactive (I built such circuits as

graduate student, at the time of Sputnik 1, in 1957). Or else, a

filling gas (alcohol or chlorine, I vaguely recall) absorbs the

ultra-violet and stops the discharge.

1.

To produce 1000 volts, you usually need (a) an oscillator

circuit to create a high-frequency alternating current (AC); (b) a

transformer converting the AC to a higher voltage (with smaller current flow); and (c) a rectifier, which only lets current flow in

one direction and converts 1000v AC to single-direction 1000v

current. That current still has fast ups and downs, but as noted, it

is only used to fill a capacitor, and once that is full--like a cup

filled to the brim--its voltage stays almost at the same level.

The electric current needed is very small--just to fill and

empty a relatively small capacitor. The problem is that both

transformer and capacitor need pretty good electrical insulation.

2.

Look up some book about electrical discharges and dischargetubes. A neon light is such a tube--nothing more than a glass

tube with some low-pressure gas in it, and two electrical

contacts at the ends.

If you connect one end to the ground and the other to a

voltage of (say) +1000volt, a current will flow (and light will be

emitted). That is more like the situation you address in your

question--it keeps going, does not operate in pulses. The

fluorescent tube is also similar--see

3.


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http://www.phy6.org/Education/wplasma.html

http://www.phy6.org/Education/wfluor.html

In the tube ions and electrons are constantly separated.

Electrons then travel to the (+) contact and ions to the (–),

where they pick up an electron and become normal atoms again

(the electrons at the (+) help complete the circuit). Appreciable

numbers of ions and electrons, however, cannot stay separated

without an enormous voltage to keep them apart.

I don't know. Many.

OK, let me try a rough estimate. However, I will have to use

scientific notation and electric terms which you may only learn

later.

Say the size of the capacitor is about 1000 picofarad, or 10 –9

farad. It is charged to 1000v, so multiplying the two we get the

electric charge, 10 –6

coulomb.

If the capacitor gives up (say) 10% of its charge, dropping

from 1000v to 900v before the discharge stops, then the counter

releases a charge of 10 –7 coulombs.

The charge of a single electron is about 1.6 10 –19 coulomb

(see your next question). So the number of electrons needed to

carry the charge is obtained by dividing

[10 –7

/ 1.6 10 –19

] = 6.25 1011

= 625,000,000,000

That is, 625 billion: the estimate may be inaccurate, but

whatever it is, the number is obviously BIG.

4.

You also need multiply by the voltage--coulombs times volts

gives energy in joules. Strictly speaking, the voltage drops during

the discharge, so if you use 1000v, you have a slight

overestimate.

5.

If an alpha particle strikes an insulated body in a vacuum, the

body's positive voltage will indeed rise. In practice, if an

appreciable stream of alphas is hitting, the voltage quickly gets

positive enough to pull electrons from the surroundings, and the

effect quickly levels off. (If somehow not enough electrons are

available--theoretically possible, practically unlikely--the

voltage will rise to where arriving alphas are repelled, and no

more charging takes place.)

In space (best vacuum we have) the problem is not so much

arrival of ions but of electrons. Spacecraft can then charge up to

50 or 500, even 5000 volts (in the aurora). That may not only

confuse scientific instruments, but also damage electronics,

6.


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when different parts charge to different voltages and a surge

jumps between them.

OK. Now sleep soundly!


8. Measuring the Earth's Magnetic Field

I am doing a sixth year studies project on magnetism in and was

delighted to find the question and reply page with topics similar to

what I had thought of studying.

I was wondering if there was a practical method for measuring the

strength and direction of the Earth's magnetic field at different

geographical locations. Any help or inspiration would be greatly

appreciated.

Reply

Is your "sixth year" in school or 6th year in college? It is not easy to

tailor an answer to fit either level!

In any case, the electronic gizmos nowadays used in space are too

complicated for a quick discussion, so let me instead describe earlier,

simpler methods.

The direction of the magnetic field is of course given by the compass

needle: but that is just the horizontal part of the force, Actually the

magnetic force also points i n t o the Earth (or out of it, in the southernhemisphere).

To find the angle at which the force points down ("dip angle") people

used a needle similar to a compass needle, but on a horizontal axis,

allowing it to swing in the various directions to which the hands of a

wall clock might point.

That is a bit harder to arrange than a compass needle: if one end of

such a needle points at an angle downwards, how is one to know

whether the magnetic force is responsible, and not, say, that the needle

is not quite balanced on its pivot, but that one end is slightly heavier and therefore points downwards? To avoid this problem one starts with

an unmagnetized needle, balances it very carefully, and only then

magnetizes it. When in 1831 the expedition of John Ross searched for

the north magnetic pole, it carried along a dip needle, and when it

pointed straight down (while the regular magnetic needle showed no

preference for any direction), that was it .

Measuring the strength of the field is harder. Take a thin long bar

magnet and hang it by a thin thread, then wait until it points north-


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south. After it does, push one tip slightly left or right and let go: it will

swing back to north-south, but will overshoot to the other side, then

turn back to the right direction, swinging back and forth like a

pendulum, gradually quieting down to point steadily. The average

length of each swing depends on two things: the strength of the bar

magnet and the strength of the magnetic force. With a stopwatch,

measure 20 swings or so and figure out how long each swing takes.

Then put a small compass needle on a table, and put the small magnetnearby, in such a position that it tries to line up the compass to point

east-west.The small magnet and the Earth's magnetic force obviously

compete fordetermining which way the needle points, and by looking

at the actual angle of the needle, and its distance from the small

magnet, we again get an observation that depends on how strong are

(1) the small magnet and (2) the magnetic attraction of the Earth.

Using these two observations and some calculation, the physicist can

find both these unknown quantities.

This method was proposed by Carl Friedrich Gauss in Germany

around 1835. It obviously won't work on an orbiting satellite--but howmeasurements are made there is another story altogether.


9. The Strength of the Earth's Magnetic Field

Could you please send me any information regarding the current field

strength of the earths electromagnetic field? My data is current as of

1975 which is by far outdated. My reading from that time were 30,000

gammas at the equator. If possible could you please send informationon the current decay of the earth's magnetic field.

Any information would be greatly appreciated.

Reply

I am not sure at what type of information you need, or to what use you

put it. The most complete information on the Earth's internal magnetic

field is in form of a set of coefficients, to be plugged into a

mathematical representation--the so-called spherical harmonic

expansion. The coefficients generally used are the so-called IGRF set

(International Geomagnetic Reference Field) chosen by a committee

every 5-10 years and based on the "best available" observations. You

can find them on the world-wide web at

http://fdd.gsfc.nasa.gov/IGRF.html

Some of these models also include the annual change of the field (but

not in the above files). You might like to search the web using (say)

the Altavista or Yahoo search engine, on the term IGRF.


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If you just want maps of the field, for instance those describing, the

variation of its strength over the globe, try

http://swdcwww.kugi.kyoto-u.ac.jp/igrf/index.html

Clicking on the map of horizontal intensity in Mercator projection

(use GIF format, which web browsers read) will show you that the

horizontal intensity around the equator varies quite a bit. but 30,000

gamma (or nanotesla, same thing) is a reasonable value. A centraldipole field would be horizontal at the equator; the average total

intensity is somewhat larger (32500 is a good average) but that may

be due to by non-dipole components.

The field has been weakening since Carl Friedrich Gauss measured it

around 1836, by about 5% per century, recently accelerating to

7%/century. The decrease in the dipole field is however accompanied

by a growth of the non-dipole (=more irregular) components, as shown

by Benton and Voorhies. This means that the field is not really

weakening, just reshuffling its field linesy, reducing the "main dipole"

(=north-south bar-magnet pattern, declining as noted by about 7% per century) and reinforcing the more complicated parts. These tend to

contribute a weaker field, because the magnetism originates in the

Earth's core, about half an Earth-radius down: all magnetic fields at

the surface are weaker than those in the core, because of the distance,

but the more complicated fields decrease faster.

Whether the main dipole will reverse in about 1300 years is anyone's

guess. Geological evidence suggests it has happened in the past, but

odds are against it, because the mean frequency of such reversals in

the past seems to be about once in 500,000 years.


10. Solar Eclipses

I'm working on a science project about the solar eclipse.

My first question is, how can you figure out exactly when the next

eclipse will come?

The next question is: What are the main theories about the incredibleheat of the corona? How can it be so warm when it's so far away from

the sun's center?

Reply

Dear Lars

Predicting eclipses is relatively straightforward, you just need to know

the motion of the Sun and Moon across the sky, and when they occupy


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the same area, you get an eclipse.

By now we have pretty good formulas for the orbital motion of the

Earth around the Sun (which determines where the Sun is in the sky)

and of the moon around the Earth, and can predict eclipses quite

accurately. The journal "Sky and Telescope" usually carries accurate

maps of where the eclipse can be seen (if the sky isn't cloudy) and the

times when it should happen. The journal also maintains an eclipse

page on the web, at:

http://www.skypub.com/eclipses/eclipses.shtml

The heat of the corona is still a great mystery. I can describe to you

one theory, but it is probably not the right answer.

When you walk along a beach, you usually see fairly large waves,

breaking on the seashore. If you take a boat past those waves, you are

likely to find that in deeper water the waves almost disappear, or

anyway are much smaller. Why?

It happens because a traveling wave carries a certain amount of

energy, which causes the water in the wave to rise and fall again. As

the wave moves into shallower water near the shore, the same energy

now moves a smaller amount of water: if energy is conserved, the

motion must be bigger, which is why waves become higher. Finally, the

water is not deep enough for the wave to keep going, and the wave

breaks, giving up its energy all at once to irregular swirling of the

water.

Some scientists have speculated that waves, perhaps similar to sound

waves, rise from the surface of the Sun into the corona. They carrymuch less energy than sunlight, but as they rise, the density of the gas

around them quickly decreases, until finally they reach a height at

which not enough gas is left to carry the wave: it then gives up its

energy, and since that energy is given to the surrounding gas, and there

is very little such gas left at those heights, that remaining gas gets very

hot.

That at least was the theory some time ago: however, scientists now

know what sort of waves can move in the atmosphere of the Sun, and

they say that such waves get reflected back downwards before they

reach high enough for this process to happen. So we really don't know.


11. Magnetometer for Observing Magnetic Storms

I am in contact with a doctor in a hospital and we would like to build a

magnetometer that measures geomagnetic storms, a normal

magnetometer, but cheap. The doctor made studies that show how

patients react to differences in the geomagnetic field. He says that it is


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possible to help them feel better, and to help hospital personal by

informing them about the geomagnetic status, allowing them to

anticipate the patient's pains...

I have experiences with microprocessor-driven machines, to build and

program them, but the problem of geomagnetic detector is new for me.

Reply

I hate to discourage someone as enthusiastic as you, but I would

recommend to reconsider your plan, for several reasons

Building a magnetic observatory is technically difficult, and so is

running it.

1.

Information on geomagnetic storms is probably easily obtained

from some convenient magnetic observatory, even for free over

the internet.

2.

I doubt very, very much in any effect of geomagnetic storms on

people. No one has ever proved anything in that direction, and it

would be very difficult to imagine a mechanism by which suchan effect could arise.

3.

In more detail:

The most practical magnetometer is a fluxgate instrument, using

a core of a ferrite with very precise saturation level. If an

external magnetic field exists, it will penetrate the core, and

magnetize it in some direction, and the core is then a bit quicker

to saturate in that direction than in the opposite one; modern

instruments use a ring shaped core. Sensitive electronics can

detect the difference in saturation.

Obviously, you need 3 such instruments to detect the

components of the magnetic field in the 3 directions of

space--say x, y and z (storms mainly affect the north-south

component). But geomagnetic storms are very small--the field

may change by 0.2% only--so one must be able to tell it apart

from all sorts of other disturbances, e.g. magnetic observations

must be made away from electrified streetcars and railroads, and

from other electric machinery. And other sources of disturbance

("daily variation" for instance, due to tides in the ionosphere)

must be subtracted.

1.

There exists a world-wide network of magnetic observatories

which do this sort of work routinely. Try contacting some local

insti- tution. Or else try the data center in Japan:

http://swdcdb.kugi.kyoto-u.ac.jp/wdc.Sec3.html

For geomagnetic data:

http://swdcdb.kugi.kyoto-u.ac.jp/magqldir/

2.


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And for real-time data of the Kakioka observatory:

http://swdcdb.kugi.kyoto-u.ac.jp/magqldir/q/KAKrtoday.html

Other data are also available there, but many of them are from

near-polar observatories, sensitive to auroral currents. Kakioka

is fairly close to the equator and therefore more suitable for

magnetic storms. To be sure, it is half a world away from where

you are--but magnetic storms are world-wide.

I doubt the magnetic field can affect pain in patients. You

cannot feel the field, even less so a variation of 0.2% in it. One

can easily imitate the field using coils and see whether patients

can sense anything, if you want.

By the way, if you want to build a magnetometer, there exist

other uses, and you can buy commercial instruments for them,

e.g. finding boundary stakes in surveying, stopping theft of

library books (marked with magnets), screening for guns at

airports, finding submarines under water, etc.

Best wishes

David Stern

3.


12. Cosmic Rays

After reading your cosmic rays report, my friend and I decided that I

would like to do a science project on cosmic rays.However, we are only eighth grade students, and therefore do not

have much background on the subject. It would be much appreciated

if you could provide us with some background on cosmic rays, and

perhaps with a science project we could perform.

Reply

Actually, you can find quiet a bit of material about cosmic rays in

"Exploration," including material you need to understand more

advanced discussions of cosmic rays.

I would recommend that you and your friend use the "index" file and

reach from there the following files, in the order listed here:

Electrons, Positive Ions, Energy, Energetic Particles, The Geiger

Counter, Cosmic Rays, High Energy Particles, Solar Energetic

Particles.

Copy them on paper, if you can. Of course, if some items are not

comp- letely clear, you will need to look up other sections as well.


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In general, our study of cosmic rays can be divided into two phases.

The first started in 1912, with the discovery that some unknown

radiation, similar to the one emitted by radioactive materials, was

reaching Earth from space. Gradually, it was identified--first as

electrically charged particles, by the fact the Earth's magnetic field

excluded some of it from near the equator (around 1922). Then it was

found that the particles had positive charge--because the field affected

unequally those coming from the east and from the west (around

1936). Finally, around 1947, photographic plates in balloons at highaltitudes recorded tracks of individual particles, finding they were

familiar ions--mostly hydrogen, some helium, and a scattering of

heavier stuff, not too different from the composition of the Sun.

Scientists also found out much about the fragments produced when

these particles hit the atmosphere (what we get on the ground is almost

entirely fragments) and measured the particles' energy distribution. It

turned out that some of them had phenomenal energies, raising the

question of what process could provide them. But looking for the

source of the rays proved elusive: it was like trying to observe the Sun

in a heavy fog. In a fog sunlight gets scattered until it comes evenlyfrom all directions, leaving no clue about where the Sun actually is.

Similarly, cosmic rays seem to be thoroughly scattered in space,

arriving equally from all directions. It is true that it is hard to bend the

path of particles with such high energies, but the energies meet their

match in the great distances of space: even a weak magnetic field can

bend the path of a cosmic ray proton, if it acts gradually over

cosmic-scale distances.

So these days the emphasis is on tracing the source of x-rays and

gamma-rays, high-energy relatives of visible light, which move in

straight lines no matter what happens and therefore tell where theycome from. It takes a high-energy particle to produce a high-energy

gamma-ray, so observing the sources of such rays tells us where in the

universe high-energy particles are plentiful, and perhaps these are

cosmic rays near their sources. The catch is that (1) these gamma rays

do not penetrate the atmosphere well, so the observation must be done

from satellites, and (2), their intensity is much weaker than that of

cosmic rays. Still, we have been looking, and discovering (e.g. see the

story of gamma ray bursts in "Exploration"). Currently NASA has a

gamma-ray observatory in orbit, doing a nice job. This area of research

goes by the name of high energy astrophysics.

I don't know how much beyond this an eighth-grader can go. The

"Resources" section lists some files you might look up, e.g. on high

energy astrophysics, and a book "Moments in the Life of a Scientist"

by Bruno Rossi, Cambridge 1990

Bruno Rossi was a pioneer of cosmic ray research and this is his own

story. He began in Italy as part of the talented group which included

Enrico Fermi and Emilio Segre, and died a few years ago as a

much-honored professor at the Massachussetts Institute of


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Technology.

Another book, by a pioneer of x-ray astronomy which covers that

aspect as well as the rest of astronomy, is "The Astronomer's

Universe" by Herbert Friedman, W.W. Norton, 1990.

Finally, your own country of Canada has contributed significantly to

the study of cosmic rays. Perhaps the science museum in Ottawa can

help you.

Good luck!


Back to the Index Page

Timeline Expanded timeline Glossary

Author and Curator: Dr. David P. SternMail to Dr.Stern: education("at" symbol)phy6.org

Co-author: Dr. Mauricio Peredo

Spanish translation by J. Méndez

Last updated 25 November 2001

Re-formatted 9-28-2004


FAQ_ _Exploration of the Earth's Magnetosphere

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