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    Does electricity need an electromagnetic field to exist in? I have never heard of a report of an electrical storm in space, only on planets.

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A complete reply to your question probably requires more study on your part. Still, let me try.

    your web site is really awesome, but it doesn't answer the one question that sent me looking for info on the web in the first place. Everything I have ever heard is that the only magnetic field that can induce a current is a fluctuating one. Per my understanding a static magnetic field does NOT cause electrons to flow, only a varying one.

    The magnetic field of the earth doesn't fluctuate around, so how is that the charged particles started circling around the lines of force. And why would they spiral in towards the N/S magnetic poles? I thought that the current is supposed to run strictly at right angles to the magnetic field??

Thanks for your help.

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    As the poet wrote, "a little knowledge is a dangerous thing." There is so much involved in magnetism, in current and trapped particles, that a short message here won't do it justice! My advice is look up my web sites on the magnetosphere and the Earth's field, and take your time.

    (1) True--a fluctuating magnetic field will induce a voltage, which can drive current, while a static magnetic field just sits there. But there exists another situation important in space (and in the dynamo mechanism of sunspots and the Earth's core): a magnetic field in a fluid conducting medium which FLOWS--where part of it moves with respect to the other. See

    Dear Dr. Stern, I have read with great interest the following page:

    My 10th grade daughter, Erica, will be competing in a Texas Symposium this year with a project in space weather. She wants to find the "best" orbit for a space station (around earth) to maintain by balancing a few factors including "space weather". Your websites have been very helpful in getting good background info and understanding.

    However, she would like to use "real" data to help form and prove her thesis. She has found some data taken from geostationary orbits, but would like some for LEO and orbits at the Lagrange points. She knows of some satellites, like SOHO at L1, Map and I believe Wind is there now. Most of the data she has is from Wind and some from ACE. However, we can't seem to find any data for L2, L4, L5 (earth-moon). Do you know if any is available and where?

    Also, she'd like to know how much power would be needed to keep a station in these orbits, assuming some "standard" orbital perturbation. We've not been able to find that kind of data either, except a correction of 25 m/s mentioned for L1 (which we can convert to power with a few assumptions). With all the hardware in LEO and geosynchronous, one would think corrections for those would be easy to find, but we haven't succeeded yet.

Thanks for your time,
Erica's dad,

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Your project sounds imaginative, but when you start looking at details all sorts of questions pop up. I assume of course you are planning a space station with human crew, not an automatic satellite.

    Sending humans to space is dangerous and expensive, and for these reasons alone, the only suitable place is LEO. Out in synchronous orbit one is exposed to magnetic substorms and storms, which inject energetic particles into the environment, and both there and at more distant locations you are exposed to energetic protons from solar flares, which are even more penetrating. I have the trace of some of those, from storms around Halloween 2003, in

My name is Carles and I am writing you in representation of a group of students from Spain who are working in a project related with space debris.

    First of all let me congratulate you for the excellent job done with your website.

    We have a pair of questions that we think that you could answer:
        -- Is the space debris electrically charged?
        - Is it because of the Earth magnetic field or the solar wind?

Thank you very much.

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    Your question is about space debris, but the same can be asked about any object in space, even regular satellites: are they electrically charged or not?

    Most satellites in sunlight have a positive potential of a few volts, because the photons of sunlight knock electrons off their skin and give them an energy of a few electron volts. This process continues until the satellite is charged to an equivalent number of volts, and then no more electrons can leave.

    If the satellite is in the Earth's shadow, this obviously stops, but then, if the satellite (or debris) is in the outer radiation belt (for instance, in synchronous orbit), it can get charged to hundreds of volts (sometimes even over a thousand) by electrons trapped in the magnetic field of the Earth. Here is why.

    In general, the radiation belt contains an equal density N of positive ions and negative free electrons. Any departure from such "neutrality" creates strong electric forces which quickly counteract it. Trapped ions usually have a larger average energy than the electrons, but because electrons are nearly 2000 times lighter, they usually move with higher velocity--say V for electrons, v for ions. A square centimeter of the surface of a satellite or a piece of debris is hit each second by kNV electrons and kNv ions--k being a factor to take into account their distribution of angles. For both kinds of particles, N is the same and k nearly the same, so many more electrons hit, and the final voltage is something like the average electron energy in electron volts. This turns back part of the electrons and attracts ions, and equilibrium is reached when the surface receives the same rate of charging from either sign.

    This won't happen in sunlight (or if it does, it's a much smaller effect) because then enough photo-electrons are driven off to balance the arriving negative charge.

    In sunlight, especially in low Earth orbit, the repelled electrons hang around at a short distance, so that any effects of charging are confined to the immediate vicinity of the satellite. The distance depends on the density of the surrounding plasma--it's of the order of the "Debye length." When charged by radiation in the Earth shadow, a similar effect occurs, even though in synchronous orbit the Debye length can be (I think) many meters. I hope all this information is helpful

Follow-up question:

Let me explain you our project: It proposes a magnetic shield for protecting satellites and/or astronauts from space debris.

    What do you think about the project?

Thank you very much.

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    Look at it this way: a satellite can orbit the Earth for years, moving all the time in the Earth's magnetic field. When calculating the orbit of such a satellite, one has to take into account, in addition to the Earth's attraction, those of the Sun, Moon and the Earth's equatorial bulge, and if the orbit is low, also of the resistance of the fringes of the atmosphere. But one never includes the magnetic field in such a calculation, because it makes no difference.

    Space debris can be a problem--see

    I wonder if a rotating giant ring of wire in orbit (or a more rigid object such as a metal ring) surrounding all around the earth would produce electricity from the changing magnetic field of earth..

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    Your Web site is very useful! I'm 45 years old, with an interest in electricity in space, and still learning.

1.     In the section on The Solar Wind, you mention that "The plasma of the corona is so hot that the Sun's gravity cannot hold it down. Instead, the upper fringes flow away in all directions, in a constant stream of particles known as the solar wind."

    Wouldn't the intense gravitation field of the Sun cause the heavier positively charged particles to fall back to the Sun, resulting in the Solar Wind containing more electrons than protons? Or would any proton falling back, attract an electron along with it?

2.     I read on a number of Web sites that the Solar Wind accelerates away from the Sun. Is there an explanation? Eg. See

        http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994kofu.symp..401T

Ian

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    Your first question is quite perceptive. A similar question about the Earth's atmosphere was addressed by Pannekoek in 1922 and by Rosseland in 1924 ("Electrical state of a star", Monthly Notices of Roy. Astron. Soc.84, 720-728, 1924). Here is the idea.

    In an atmosphere consisting of a gas of molecular weight M, the density falls off exponentially, at a rate which depends on M, on the temperature of the gas and on the force of gravity. In the Earth's lower atmosphere, the density falls to one half every 5 kilometers or so (or else, by a factor e = 2.71828.. about every 8 kilometers, a distance known as scale height H). High temperatures and low M increase H and spread out the atmosphere, while strong gravity decreases H and makes the atmosphere more compact. Of course, the Earth's atmosphere is really a mixture of gases, but in the first 100 kilometers, enough collisions occur to create a single scale height, some sort of average among the components.

    Above 100 km collisions quickly become rare, so different gases with different M tend to separate, as has been observed. Pannekoek and Rosseland wondered--what about free electrons in the outer layers of a star (or for Earth, in the ionosphere)? Their mass is so small, that their scale height should be much larger. Their layer should extend to great height, while the heavy oxygen ions (the main positive component) should stay well below them.

    They concluded this was not possible, because even a very slight separation of positive and negative charges would create an "ambipolar" electric field, pulling electrons down and O+ ions up. The field would effectively "add weight" to the electrons and would "buoy up" the O+ ions, until effectively each species senses the same downward force, contributed by both gravity and electric forces. With both species having the same "weight", they also will have the same scale height, and the ionosphere would stay electrically neutral, as is observed.

    The corona of the Sun behaves the same way, although the ambipolar field is probably much stronger, because of the high temperature.
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    I am less certain about the second question--the solar wind is really not my field of expertise. In the Earth's lower atmosphere, temperature decreases with height, because heat from sunlight is mainly absorbed by the ground, at the bottom. It is then transported by air flows and by radiation, absorption and re-radiation (by "greenhouse gases") until it gets high enough to be radiated to space, not to return. That height defines the bottom of the stratosphere; other interesting effects occur higher up (e.g. absorption of UV by ozone), but we ignore them now. Because of the upwards flow of heat, the temperature is highest near the ground (where heat comes in) and decreases with height, up to the level where heat is given up.

    Solar physicists expected the same to hold for the Sun, also heated from below, and it is still a mystery, why so much heat is deposited in the corona, making it much hotter than the photosphere below it. Still, once you get to the corona, you would expect the temperature to gradually decrease with height, as one gets away from the source of heat and as the rising gas expands.

    I have experienced seeing the polar aurora in Maryland at least 3 times in 4 years. Is this unusual? If so, do you think we are experiencing more geomagnetic storms then in the past and if so, why do you think this is so?

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    Looking for an answer to my question, I landed on your web site to find out that more or less the same (!) question had popped up several times already. This concerns possibility of a correlation between ozone depletion and the Earth's magnetic field in combination with solar effects.

    Has the possible connection between the steady decrease of the earths magnetic field and the decrease of magnetic particles (such as ozone) at times of solar bursts been investigated?

    Could this be an alternative explanation for the chemical reduction of ozone levels as suggested by a fellow country man in 1995 (I'm not into politics)?

    The especially thin layer of ozone in the arctic during winters, on average, coincides with the tail of the magnetosphere rather than the lack of newly produced Ozone?

  --- The thin layer of ozone on the poles corresponds with the outgoing flux-lines?
  --- The "Brazilian gap" in the atmosphere coincides with a local magnetic anomaly?

    The chemical explanation is solid, but doesn't explain how gaps in the ozone layer recover at random/differing speeds. It doesn't seem to correspond to temperature. If it was just a chemical reaction, ozone would be transferred to the poles at a rate that corresponds with the intensity of the chemical reaction.

    I'd be grateful if you could shed some light on this puzzle.

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    Ozone is formed by ultraviolet sunlight at altitudes between 25 and 40 kilometers. To escape from Earth along a magnetic field line, an ozone molecule would have to meet several conditions:

---It would have to be ionized--otherwise it is not affected by the magnetic field.
--- It has to have enough energy to escape gravity, and
---it must start off high enough so that collisions do not take that energy away.

    While the atmosphere is quite rarefied at 25-40 kilometers, it still is dense enough for frequent collisions between molecules; the last collisions occur around 100 km or slightly higher. I do not know if ozone molecules can survive an ionization event without breaking up, and I do not think they have enough energy to escape.

    Oxygen ions DO escape from the polar region along the magnetic field lines of the tail (which are connected to the poles all year round), as something called the "Polar Wind." These however are mainly O+ ions starting from the ionosphere, where temperatures (and energies) are higher and collisions are not frequent.

    The ozone layer is governed by a balance between processes which create ozone (from ordinary 2-atomic oxygen molecules) and the ones that remove it. In the winter polar cap, sunlight (which produces ozone) is absent, so the ozone layer is mostly governed by processes which remove ozone. For instance, if there exists enough wind to mix this layer with lower latitudes where ozone is produced even in winter, the layer will persist.

    In recent years, a "hole" was observed to form during the polar night, and that was taken as evidence that an additional removal mechanism, proposed (by Rowlands and Molina, I think) has become effective. That is catalytic breakup of ozone in the presence of chlorine, produced by the breakup of "Freon" refrigerants in the upper atmosphere, under the action of ultraviolet sunlight.

    I know of no "Brazilian gap" in the ozone layer. There does exist a "south Atlantic Anomaly" in the radiation belt, where it descends to lower levels, but that is not related.

    I noticed the time line you have at http://www-istp.gsfc.nasa.gov/Education/whchron.html titled "Some Dates in the Exploration of the Magnetosphere"

    Do you happen to know who first noticed Sunspots, and when that was?

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    Earlier observations with the unaided eye have been reported--e.g. in China and Russia--because when the rising or setting Sun is viewed through a thick haze, big sunspots can be distinguished (a few years ago I even watched that way a big double sunspot). But astronomers did not pay much attention.

        The most thorough early study was made by Scheiner, who apparently introduced the safe observation method of projecting the Sun's image onto a white surface, and who published his findings in 1630 in the book "Rosa Ursina Sive Sol."

Dear Dr. Stern:

    I came across your web site this morning and wondered if you could answer a very basic question. My daughter (age 13) is doing a science experiment involving a homemade magnetometer. She has suspended a magnet inside a soda bottle, attached a mirror to it, and there is a laser beam that is focused on the mirror at approximately a 45 degree angle. This projects a point on a chart on the wall approximately 3 feet away.

    She/we have been randomly making recordings of the magnetometer since late November/early December. Readings are taken either 10, 15, or sometimes 30 minutes apart for a period of two-three hours at varying times of the day. Because we were aware of the activity on the sun 1/15/05, we decided to do readings 10 minutes apart yesterday for as long as we could. We began at 8:00 a.m. and, with the exception of missing here or there, continued until 12:30 a.m. It is reported that there also may be sometime of geomagnetic storm even today (spaceweather.com).

    Question: What would we see on the magnetometer that would demonstrate to us that some type of unusual magnetic activity appeared? The readings yesterday started off (on a centimeter scale of 1-27, with 15 being the center of the scale) usually are between 8-10, but have been known to be as high as 24-27. Yesterday, they hovered between 9-11, when they suddenly went up to 14-16 and stayed there for some time before eventually falling back to 12-13. Another phenomenon is that the laser beam will often be right on the line, then jump about 1-2 cm above the line or below the line. Is any of this significant?

    Thank you for your consideration. We can't find any place that answers these questions and I hope you can help. We have kept all other factors constant. We have noted if there has been any home disturbance that might affect the magnetometer and its readings (heat going in house, dryer running, etc

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    What you are trying to observe is a very small effect, probably far beyond the capability of a home-made magnetometer in a soda bottle. The magnetic field at your location has an intensity of about 50,000 nano-Tesla (nT) whereas a magnetic storm may add to it about 50 nT. Even if the addition were at right angles to the prevailing magnetic force (actually, it is almost anti-parallel) it would only shift the light spot (at a distance of 1 meter) by 1 millimeter.

    That is very little, and sources of "instrumental noise" can produce equivalent results. If the suspension is an ordinary twisted yarn, the twist may absorb or lose moisture and change. Static electricity may play a role... hard to tell. I would not expect much from such crude experimentation, which must have been suggested to you by some other source.

    Some big magnetic storms occurred at the beginning of last November 2004 [letter was dated January 2005]--see
            http://www.phy6.org/Education/wmagstrm.html
We are currently still in their after-effects, a weakened field due (apparently) to a large reinforcement of the population of ions trapped around Earth from that time. See:
            http://www.antarctica.ac.uk/SatelliteRisks/lastweek.html
which will tell you, at any time, about ongoing storms, and also
            http://www.antarctica.ac.uk/SatelliteRisks/dst_nowcast_month.png

As these graphs show, a few small magnetic storms occurred since then, but nothing special.

    If your daughter wants to learn more about magnetic storms and magnetism, I would recommend files of my own web material, all linked at
            http://www.phy6.org/prospect.htm

The instrument she built is a crude version of one introduced by Coulomb--see section #5 in
            http://www.phy6.org/earthmag/mill_3.htm

At one time professional magnetometers were built like that, but with many refinements, e.g. the magnet was suspended from a long quartz fiber. I believe that today's instruments are all electronic, e.g. see
            http://www.phy6.org/earthmag/magmeter.htm

Further Correspondence:

    Oh, one other thing--the magnet is suspended by a cotton thread through a straw which is glued to the top of the magnet. We've kept the humidity and temperature constant in the room, but the idea of moisture being absorbed by the thread is an interesting one. I have still yet to figure out what causes the beam to vary 1-2 cm in vertical orientation and maybe that is an explanation. Thanks for the suggestion.

Further response:

    I'm doing a project at school, which involves the weather, and I would like to know some basic info to help me with my work. Many of my friends are going to focus around storms, twisters etc. but I would like to find out which factors affect the weather.

    More specifically I would like to know if geomagnetic waves or electromagnetic waves affect the weather.

If not, please I would like to know some of the factors that do.

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    Weather systems are driven by the Sun's heat, carried to Earth by sunlight. It is true, sunlight DOES consist of electromagnetic waves, but I don't think you were referring to light waves. Sunlight deposits heat, and both weather and climate are the result of processes by which Earth returns that heat to space. (Of course, all this heat MUST be returned, otherwise Earth would get hotter and hotter!)

    The amount of energy in that heat is huge, while the energy provided to the surface of Earth by (for example) processes in the magnetic field of Earth is small. Furthermore, magnetic variations usually affect materials which conducts electricity well, while the atmosphere in which we live is an excellent insulator.

    I wrote about weather and climate in
            http://www.phy6.org/stargaze/Sun1lite.htm
and in the two sections which follow it. (Section S-5 in that group explains what makes light "electromagnetic"). You might like to look there. If perhaps you want to write about lightning, see
            http://www.phy6.org/stargaze/Svandgrf.htm

Hi Doctor Stern,

I am a retired history teacher here in Toronto, Ontario, Canada.

    I am investigating the possibility that ancient civilizations might have been able to see the polar pillar cusp with the naked eye.

    I realize that it extends up much higher than the auroral oval but am wondering if there are any circumstances that you can identify and possibly describe whereby the polar pillar cusp might have been visible to the ancients globally?

    I appreciate the time you are making to help people who don't have a background in this field understand it.

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•     The Federal limit for exposure to US workers is 5 REM/year (10CFR835). Did NASA's Apollo astronauts get special permission to exceed this limit for the Apollo missions? 25 Rad = 25 REM. Their travel through the Van Allen Belts and the amount of time they spent outside the Belts would have given them doses far beyond this limit.

•     NASA has never directly addressed how the Apollo astronauts were shielded. Lead is the only effective shielding (which was not used during these missions). The radiation levels outside the Van Allen Belt far exceed the 200-300 RADs inside the belts. Again how were they shielded? Regardless, their doses would at least have made them sick from radiation exposure to skin and organs even if it didn't kill them. None of them suffered any ill effects.

•     Apollo astronauts were not protected from solar flares which were at their worst during this period. There is no way that the dose reports from the missions are accurate.

Thank you for your response!

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1.     I suspect that the Apollo astronauts did exceed EPA permissible doses of radiation--not by enough to pose danger to life, but above the level accepted for the population in general. Knowing NASA's concern with bureaucratic protocol, I would not be even surprised if astronauts were made to sign a waiver.

       So what? If I were an astronaut candidate, I would sign such a waiver in a heartbeat. If I am about to be launched atop a giant rocket into the vacuum of space, perhaps to the Moon, certainly facing a fiery reentry before returning home--then the risk from a moderate dose of radiation ranks far below other dangers!

2.    The actual dosage may be 25 Rad in the inner belt, (though probably less, see below). The radiation rates in the outer belt are smaller, not larger. Lead, by the way, is not an especially good shield: it is wonderfully efficient in excluding x-rays of, say, 100 keV, but radiation in space consists of particles, fast electrons and ions. The inner belt is mostly protons of about 50 MeV and is not very penetrating--the spacecraft heat shield, tanks etc. may shield the occupants somewhat, the interior of their bodies gets less radiation, too and lying close together during the belt passage they also shield each other somewhat.

       Electrons of MeV energies in the outer belt are more penetrating, but there are not enough of them. Remember--communications and weather satellites operate in synchronous orbit, in the heart of the outer belt, year after year!

3.     Solar flares can emit ions of 0.5 to 5 GeV, and these are bad, if intense enough. Such events however are rare, and when they occur, the dosage is usually not lethal, though the margin is smaller. For the Apollo astronauts, this was another calculated risk, and nothing happened.

       Now if you were to fly to Mars--a trip of 8.5 months each way, plus a forced wait on Mars, whose atmosphere is too thin to protect--solar eruptions could be a problem requiring attention (though not insoluble). But we are not at that stage yet.

    I am a sophomore in college. I am doing a physics lab about understanding the motion of a charged particle in the presence of an electric and magnetic field to estimate the mass of the electron. My question is would it be possible to use the earth's magnetic field to deflect the beam and how large a tube would you need?

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    In the lab, though, with short distances, you want to use a stronger magnetic field. Besides, if you use an artificial magnetic field to deflect electrons, you can switch it off and find its effect by comparing deflections with and without. You can't well switch off the Earth's field for calibration.

    You realize, of course, that the deflection depends on the ratio e/m, between the charge and the mass of the electron. You won't have the mass of the electron unless you can measure "e" independently. That is what Millikan's oil-drop experiment is for--right?