how to make maglev trains model

1
Cut a length of track to 2 feet-by 3 inches wide using your balsa wood or cardboard.

2
Build walls of the track from the excess material. If you are using Balsa wood, cut four 1-1/2-inch wide strips to run along the 2-foot length of the track, and glue pairs of strips together. If using cardboard, cut 2-foot-by-3-inch strips and fold them along the middle.

3
Glue the walls of the track onto the track so they are between 2-1/2 and 2-1/4 inches apart along the entire length of the track. The walls should be 90 degrees from the track.

4
Glue 12 of the magnets in a row along the center of the track. Ensure that all of the poles on these magnets are pointing the same directions. If you have the north side of the first magnet pointing upward, be sure that all of the magnets are north side up. Leave the track to dry overnight.

5
Glue two magnets to your block of wood. Verify that the poles pointing upward on the block are the same as the poles pointing upward on your track. If your track is north side up, glue the magnets so the north side faces outward and the south side sticks to the wood block. Leave your block to dry overnight.

6
Place your wooden block, or train, in the track. The magnet should hover over the magnets on the track, guided by the rails on the sides. Push the train gently to send it floating toward the ends of the track

MAGLEV TRAIN

                                                      

SIMPLE MAGLEV TRAIN
(c)1996 W. Beaty

A truely levitated maglev train is a very complex device. Permanent magnets alone cannot suspend a train car. You'd also need coils, amplifiers, and negative feedback too. I'd only recommend the coils/sensors approach if you are a college student or fairly advanced highschooler.

                           MAGLEV TRACK,
          board          VIEW FROM THE END         board
          ____                                      ____
         |    |                                    |    |
         |    |                                    |    |
         |    |        magnet         magnet       |    |
         |    |        row            row          |    |
         |    |     _____                _____     |    |
       __|____|____|_____|______________|_____|____|____|__
      |____________________________________________________|
                        wood or cardboard

However, there's a way to make a simple permanent-magnet maglev train. Instead of using coils and electronics, we just put guide rails on the sides of the track. The guide rails will lightly touch your train and keep it centered. Because real science involves striking out into the unknown, I'm not going to give detailed plans here. Just enough info to get you started.

The lifter-rails under your train will be small square ceramic magnets. Radio Shack stores in the US sell a good type, the 1" x 3/4" square with a hole in the center. Each foot of train track will require 32 of these magnets. Less expensive magnets are available from All Electronics, but I haven't tried these (see links at end of article).

First mark one pole on all of your magnets so you later can lay them down with the same pole facing upwards. To do this, stick your magnets all together in one big long stack. Now use a permanent marker to make an "X" on flat face of one end of the stack. Pull the marked magnet off the stack, make an "X" on the next one, etc., until you're out of magnets. Mark every single one on the same side.

Before building an entire huge track, make a "test bed" about one foot long. For a base, you can use cardboard or wood. Don't use iron or steel of course. You'll be lining up your magnets side by side in long rows. One way to do this is to stick them to a strip of duct tape, then lay the strip down on the cardboard or wood and rub the tape down to hold the magnets underneath. Position each magnet carefully on the tape so the row is very straight. Make two parallel rows of magnets with about 5cm of space between the rows. Make sure the rows are perfectly parallel. It might help to measure with a ruler and draw lines on the base first.

For a temporary "car", cut out a square of cardboard 9cm by 15cm . Tape four magnets to the corners, flipping the magnets correctly so they will repel from the tracks when the cardboard is layed down. Position the magnets on the cardboard so they will be exactly over the magnets on the track.

If you place your cardboard "car" on your magnet track, you'll find that it will twist or flip over and fall, and will not hover. But if you gently hold it by its sides, you can keep it floating in position. Does this give you ideas? What if you place one long board on each side of your track? The "car" will touch the two boards and will stop slipping sideways, but the boards will not stop the car from slipping down the track.

               MAGLEV TRACK, WITH FLOATING
               CARDBOARD CAR IN PLACE   
    ____       (end view)                     ____
   |    |                                    |    |
   |    |                                    |    |
   |    | __________________________________ |    |
   |    ||__________________________________||    |
   |    |    |_____|              |_____|    |    |
   |    |     _____                _____     |    |
 __|____|____|_____|______________|_____|____|____|__
|____________________________________________________|

Once you get this part working, you can build a much longer track. You can build a real car too, one that looks like a train, although you'll have to find very lightweight construction materials. You can try thinking up ways to reduce the friction with the side rails. Maybe try aluminum angle strips instead of wood, or sand the wood smooth and paint it with something hard and shiny.

 

birth of univers

Our universe began with a singularity that exploded, some 15-17 billion years ago. The explosion created space and time as we know it; some of the expanding energy from this 'Big Bang' became mass, mostly hydrogen and helium, fused by the billion degree temperatures that existed following the explosion. 

An astrophysicist named George Gamow postulated in the 1940's that if you looked deep enough into space, (about 99% of the way back to the beginning) you would be looking backwards in time, and should be able to see some left-over radiation from this original explosion that created our universe. The great time and distances involved (over 140,000,000,000,000,000,000,000 km, or more than 14.7 billion light years), would have converted the radiation into lower energy microwaves. 

Two radio astronomers named Arno Penzias and Robert Wilson found this microwave radiation in 1965, quite by accident. For this accomplishment they received the Nobel Prize for Physics in 1978. 

This cosmic background radiation is all that is left over from the original explosion that created our universe. It can be heard as a hiss by listening to speakers hooked up to a radio telescope ... that's how Penzias and Wilson originally discovered it. But you can see a visualization of this energy by tuning your television to an unused channel. About 1% of the static you see on the screen is caused by radiation left over from the Big Bang

Weightlessness!

Weightlessness!

I'm sure you've seen astronauts in the Shuttle, on T.V., and marvelled at how they seem to float around,... almost as if there were no gravity! Have you ever wondered about the things they nevershow on TV... like, what happens if somebody throws up? How do they go to thebathroom?? Believe it or not, these are actually important questions; they pose problems that scientists have been trying to answer for almost 40 years! Before we show you their answers, we need to clear up a very common misunderstanding. When an astronaut in orbit is seen to be floating around his spacecraft, he is indeed 'weightless', if you mean by this, 'He would weigh nothing if he were standing on a bathroom scale'. But it is wrong to say that the force of gravity on him is zero, or that 'there is no gravity'. He is 'weightless' the same way you would 'weigh nothing' if you jumped out of an airplane and were falling freely toward the ground. If a bathroom scale was falling freely beside you, and you tried to stand on it, it would register your weight as zero, because it's falling too. But both you and the scale are still under the pull of the earth's gravity. The force of gravity isn't zero, just the weight you'd measure on a scale. In the space shuttle, both the shuttle and the astronauts are falling freely around the earth. That's what an 'orbit' is. Imagine you were inside a big box that someone pitched out of an airplane. You would be floating around inside the box as you and it fell together. Rather than saying the astronauts are 'weightless', it makes more sense to say they are 'continuously falling'... from a height so great that the earth 'curves out of the way' underneath them, so they never hit the ground! The force of gravity at their height above the earth is only slightly less than it is right here on the surface! Astronauts train for this unsettling experience by flying as passengers in the empty cargo compartment of a large plane. (it has been a KC-135, now going to a DC-9). The plane flies upwards in a smooth arc, reducing the throttle as it climbs. The plane begins to fall in a long, smooth, parabolic path. Everyone inside the plane falls along with it; if they aren't strapped down, they float around just like they would in space. In fact, the effect is identical. Actors (including Tom Hanks) in the movie 'Apollo Thirteen' underwent this procedure in order to film the 'weightless' scenes in the movie. The actors ended up having more time 'weightless' than many former astronauts in space ever did! Astronauts often get sick the first time they experience 'weightlessness'. Some always get sick. This can be very unpleasant in the close confines of a spacecraft, since everything floats around, including the vomit! It tends to congeal into large spherical globules that float around the cabin with the air currents. Aside from the unpleasantness of breathing in the stuff, or having it float onto your sandwich, astronauts also have to prevent it from gumming up or shorting out the equipment. The mess is very quickly cleaned up with a vacuum cleaner... which is perfect for sucking errant bits of stuff out of the air! A liquid that the astronauts want to drink, water for instance, can be slid out of its container, where it will hang in the air in a big 'blob'. It can be sucked up with a straw inserted into the 'blob' of water! After consuming a certain amount of liquids or solid food, all astronauts will sooner or later have to visit the bathroom. This presents certain problems in space, as the liquid or solid waste doesn't 'fall', it just floats! (Actually, of course, it's falling with youaround the earth). The earliest spacecraft allowed occupants almost no room to move around; the 'toilet' consisted of, for men, a vacuum tube that you plugged into in front, and a big bag with sticky tape around the mouth that you stuck on behind (so to speak). The arrangements were similar for women, except that the one in front went inside (and was described by many female astronauts as an 'instrument of torture'). The Shuttle's facilities are a little more up-to-date... but not much. Essentially the urine collection is done the same way, except that you can go to the tube (you don't wear it). Solid waste is collected by something that acts much like a real toilet, except the waste and flushed water are vacuumed away. It does plug up occasionally. Probably the first real toilet will have to await the construction of a large, rotating space facility, where rotation causes a centripetal force that simulates gravity. (Imagine a tiny 'you' standing on the bottom of a bucket that someone is swinging around their head. You would feel 'heavy' in the direction of the bottom of the bucket. Amusement park ride builders know this.) Such rotating 'space stations' might supply a sort of 'gravity' for your toilet... but then you'd have the problem of Coriolis forces...

orbital velocity

Bodies which orbit a large mass move at velocities which depend on their distance from that mass. In the animation at the right, you can see two planets orbiting the sun. The planet closest to the sun moves faster than the planet further away.

The velocity of the orbiting body does not increase linearly; the relationship is such that the velocity increases inversely as the square root of the orbital radius:where G is the gravitational constant, and M is the central mass.

For example, if one planet were 16 times farther from the sun than another, its velocity would be one quarter of the other planet's.



The important principle here is that as an object moves closer to the body it is orbiting around, its velocity increases.

Here is a simple demonstration you can use to illustrate this fact. You'll need a metre or two of string, a strong plastic straw, a weight of some sort, and a handle.
We used an old roll of tape for a handle, and a large nut for a weight.


The aim is to spin the weight in a circle, while holding the straw in one hand and the handle with the other. By holding the handle in position near the bottom of the straw, you can make the weight maintain a steady circular orbit.

Be careful: you might consider using a weight that won't cause too much damage if it hits you in the head. We overlooked this danger, and paid the price! 


This is what should happen after you get the weight spinning.
You will feel a strong force pulling the handle upwards, which you must counteract with a force of your own, to maintain the circular orbit. The force you apply is analagous to the gravitational force.

This demonstration all by itself will let you calculate the velocity of the orbiting weight. Measure the radius of the circular path, work out the circumference, and divide this by the time for one orbit. (The latter value can be obtained by timing 20 orbits and dividing by 20) 

Now pull down on the handle. Keep pulling until the weight has moved inwards, and is moving considerably faster. This clearly illustrates that a shorter radius of orbit results in a higher velocity.

Once again you could calculate the velocity of the moving weight. In fact, you can make a very nice graph of velocity vs radius, by calculating and measuring both values for a series of different radii. What do you think the graph would look like?

Mathematically, you could then describe the relationship between   v and  r, using the regression menu on your TI83+ calculator.

This little demonstration can lead to a number of interesting mathematical explorations! 

super nova

A Star Is Born
Stars are continually being born in our galaxy and others, as dense concentrations of gas and dust contract under their own gravitational forces. As the material falls inward, it eventually becomes hot enough to begin nuclear fusion. At that point, the star 'turns on', and its radiation begins to blow the remaining dust and gas away. Our own sun was formed this way, some 5 billion years ago. Much of the gas and dust that forms new stars contains heavier elements that were manufactured in supergiant stars which exploded long ago, (called supernovas), scattering their insides across space. 

Born only about 100,000 years ago, material streaming out from this newborn star has formed the nebula called Sharpless 106. A large disk of dust and gas gives the nebula an hourglass shape, and emits light after being ionized by an infrared source somewhere near the centre. It also reflects light from the newborn star. This image also reveals hundreds of low-mass brown dwarf stars, hidden in the nebula's gas. This entire nebula spans about 2 light-years, and lies about 2000 light-years away from us, toward the constellation of Cygnus.

In nearby galaxy NGC 6822, this glowing nebula surrounds bright, massive, newborn stars. A mere 4 million years old, these stars condensed from that galaxy's interstellar gas and dust clouds. This nebula is very similar to the Orion Nebula within our own galaxy, but it is much brighter ...at a distance of 1.6 million light-years, it is about 1,000 times farther away. It is also ten times larger, being about 100 light years across.

the space

The Odyssey spacecraft arrived at Mars on Oct. 30, 2001, after an interplanetary journey lasting 200 days, firing its main engine in order to be captured into orbit around the red planet.

---

We already know quite a bit about this nearby planet, from previous orbiting space probes and landing craft. Beginning with the first Soviet attempts in 1960, around 30 missions have visited the planet, although only 10 or so have done so without problems. 


Mars' atmosphere is thin, cold, dry, and nearly all carbon dioxide. Strong winds blow at speeds exceeding 100 miles per hour, causing large dust storms, which erode the surface. These winds are caused by slightly warmer temperatures on Mars as it gets nearer the sun in its orbit; Mars' orbit is much more eccentricthan earth's. 

The huge dust storms combine with carbon dioxide ice in the atmosphere, creating a haze in the air, and causing the sky to appear yellow, as shown in the Viking Lander photograph at the right. See a 3D panorama of Mars. (red/green glasses needed)

Earth's blue sky is caused by the scattering of light in the atmosphere by objects which are small in comparison to the light's wavelength. Visible light from the sun contains a mixture of colours, each corresponding to a different wavelength. Sunlight streaming into the Earth's atmosphere from one direction is scattered in all directions, as it encounters air molecules. Shorter wavelengths of light (the blue end of the spectrum) are scattered more than longer wavelengths (the red end of the spectrum). An observer perceives blue light coming in from all directions, so the sky appears blue. If there were no atmosphere, the sky would appear black, like the sky seen in Apollo pictures from the moon.
On Mars, some of the dust particles in the air contain magnetite (a black, opaque mineral) which absorbs sunlight more effectively at blue wavelengths than at red wavelengths. In addition, larger dust particles both reflect and absorb sunlight. These factors result in Mars' yellowish sky color. 

Mars' rotational axis is tilted at an angle of 25°, much like Earths (at 23°) This causes Mars to experience 'seasons', as one hemisphere or the other is tilted towards the sun during Mars' orbit. Temperature changes cause large winds, hazier sky, and many cirrus-like clouds of carbon dioxide. (There are no water clouds in the Martian sky; because of the temperature and pressure, water turns from solid to gas.) 

The Martian atmosphere 3.8 billion years ago was thicker, warmer, wetter and more able to support life. Over the following billions of years, most of it has escaped into space. Today, very little water vapour can be found in the Martian atmosphere. If all the water in the Martian atmosphere were to turn to rain it would make a puddle less than a hundredth of a centimeter deep. The source of this small amount of atmospheric water vapour are the polar caps, from which tiny quantities of water vapour sublime during spring and summer. In addition, there is about 10 times this amount of water in the top few centimeters of the Martian soil.


The pattern of crater erosion on the surface of Mars indicates a surface drainage flow of some kind. This tells us that the atmosphere must have been significantly warmer at some point in the past, warm enough to allow substances, at least temporarily, to assume liquid form. Scientists speculate that CO₂ was released in sufficiently high amounts by volcanoes to create a greenhouse effect and warm the planet, allowing liquid water to flow temporarily and erode the surface. It is this supposed existence of ancient liquid water which allows for the possibility of life (at some time in the past) on Mars. Perhaps pockets of life remain, clustered around small sources of water, under the soil.

Volcanoes There are many inactive volcanoes on Mars. The largest shield volcanoes are basaltic, like volcanoes in Hawaii and Iceland. Olympus Monsis one such volcano, and is the largest mountain feature known anywhere in the solar system; it is so large, it would cover the state of Arizona.

           Canyons

The surface of Mars also includes many of the largest canyons in the solar system. Valles Marineris is the largest of them all. This huge canyon system is 5,000 km long, up to 240 km wide, and 6.5 km deep. If this canyon were located in the United States, it would stretch all the way from California to Virginia.

The picture at the left shows west Candor Chasma, one of the connected valleys of Valles Marineris. This section is about 150 km wide. The light-coloured rubble-filled areas may be deposits resulting from the collapse of the walls of the canyon due to the melting of ice at some point in the past. 

Moons Mars has two small, irregularly shaped moons, called Phobos and Deimos. Much of what we know about them comes from the Mariner, Viking and (Soviet) Phobos missions. In 1977, Viking Orbiter 1 did a flyby of Phobos, the larger, inner Martian moon, coming within 90 km of the surface. At about the same time, Viking Orbiter 2 flew by Deimos, the smaller moon, at a distance of only 22 km. Pictures revealed details as small as several metres.

Deimos

Phobos

The Soviet Phobos missions were probes intended to land on Phobos. While these missions took many photographs of Phobos, both probes were unsuccessful at landing on the surface.

One of the most unusual features of Phobos, aside from its irregular shape, is the huge crater, named Stickney Crater, on one end. Phobos itself is only 28 km long and 20 km wide, so the moon must have been nearly shattered completely by the force of the impact that caused this crater. Surface fractures are evident in the photo (right) of Phobos' surface; these grooves are about 700 metres wide and 90 metres deep near the edge of the crater.

Both moons are very similar in composition, size, and shape, to asteroids; it is possible that they were in fact originally asteroids, captured by the gravity of Mars, ... although one or the other may have also formed by material accreting during the formation of Mars itself. No definitive answer to how the moons were formed is accepted by all scientists, as of this writing. 

Previous NASA missions to Mars have revealed much about the surface of the planet. A Mars Rover released on the surface was controlled from Earth, and before contact was lost, returned some spectacular pictures of the rock-strewn landscape.

Mars' reddish colour is the result of iron oxide (rust) in the soil, and the surface is eroded in many places by dust storm activity. So far, no evidence of living material or water has been found, although the exploration to this point has been extremely limited. 


Indirect evidence of life on Mars was recently released when researchers found magnetic material in several 3 to 4.5 billion year old Martian meteorites, that could only have been produced by bacteria. The meteorites, found on Earth, made their way here after being blown from the surface of Mars by huge crater-forming impacts of large objects. Both meteorites show evidence of microfossils and other remnants of early life. Clusters of very small spheres found in the meteorites are very similar to those seen in bacteria-containing samples from deep beneath the Earth's surface. They are embedded in clays that are clearly of Martian origin, suggesting that they too were formed on Mars. 

Further evidence from the meteorites includes magnetite crystals identical to those produced and used by aqueous bacteria on Earth. Additional studies showed that a substantial portion of the hydrocarbons found in the meteorites were in them when they left Mars, and are not the result of terrestrial contamination. There is also evidence that most of the carbonates in the meteorites were formed when Mars was warmer and wetter - an environment much more favourable to life than the current surface of Mars. 


Odyssey won't be alone at Mars. The Mars Global Surveyor spacecraft has been in orbit around Mars for about four years. The photo at the right is a view of the Martian south polar region, taken in September 2001. 
The bright area at the center is the permanent south polar cap, the part that will remain through the summer. The bright areas surrounding the center are the seasonal frost cap that is deposited during winter in the southern hemisphere. The hazy zone that covers most of the left side of the image is afternoon clouds and fog. 
The polar frosts contain both water and carbon dioxide ices. Clouds of condensing water ice crystals are common.

To get an idea of the surface area covered by this photo, the permanent cap at the center of the image is about 420 km (260 mi) across. Sunlight illuminates the scene from the upper left 


Now that the Odyssey and other spacecraft have reached Mars, we should soon be learning a lot more about this planet. The probe is very sophisticated, and includes an instrument package called Themis. When Odyssey is in its mapping configuration, with the solar panels fully extended, it will be able to take detailed photographs of the surface, using visible light as well as other wavelengths.

After entering orbit, the craft will use aerobraking (friction with the upper layers of Mars' atmosphere) to eventually end up in a circular 2-hour orbit, only 400 kilometres above the planet's surface. Odyssey's instruments and cameras will explore the climate and geology of Mars, including a search for water and evidence of life-sustaining environments. 

Two rovers have also recently arrived on the surface of Mars. Have a look at a large spectacular panoramic view of the surface of Mars taken by the rover Spirit. This large image may take a minute or two to load.

Below is a panoramic image of the Martian sunset also taken by Spirit, in 2005. Twilight on Mars lasts for about 2 hours; the long duration is caused by sunlight scattered around to the night side of the planet by high altitude dust. Similar long twilights sometimes occur on Earth when tiny dust particles are erupted from powerful volcanoes. 



Have a look at more recent Mars photographs

Some of the information and photographs on this page relating to the Mars Odyssey mission were obtained from NASA's own excellent site The Odyssey Mission. Visit this site for more detailed information about the mission, and up-to-date results. 

nuclear fusion

Nuclear fusion is the energy source of the future. It is what provides the sun and the stars with the energy to shine continuously for billions of years. Fusion has been used here on earth to produce nuclear bombs, but has not yet been controlled so that we can obtain useful energy. We will try to show how fusion works, and describe current efforts to tame this limitless energy source.

Fusion is what happens when two atomic nuclei are forced together by high pressure ... high enough to overcome the strong repulsive forces of the respective protons in the nuclei. When the nuclei fuse, they form a new element, and release excess energy in the form of a fast-moving neutron. The energy is 'extra' because the mass of the newly formed nucleus is lessthan the sum of the masses of the original two nuclei; the extra mass is converted to energy according to Einstein's equation E=mc2 This energy can be used to do useful work! The nuclei used by the sun, and in experiments on earth, that undergo fusion, are two isotopes of hydrogen called deuterium and tritium. The simple hydrogen atom, which has one proton in its nucleus, has two isotopes ... similar forms of hydrogen, but with extra neutrons in their nuclei. One is called deuterium, the othertritium. You can see the fusion process happening with these two nuclei, in the diagram at the top of the page. The first generation fusion reactors will use deuterium and tritium for fuel because they will fuse at a lower temperature. Deuterium can be easily extracted from seawater, where 1 in 6500 hydrogen atoms is deuterium. Tritium can be bred from lithium, which is abundant in the earth's crust. In the fusion reaction a deuterium and tritium atom combine together, or fuse, to form an atom of helium and an energetic neutron. It only takes a small amount of these isotopes to produce a lot of energy! The deuterium-tritium fusion reaction results in an energy gain of about 450:1!! No other energy source we can tap releases so much energy for the amount that is input. In fact, both the extra neutron and the new helium nucleus (called an alpha particle) carry off excess energy which can be used (to heat water, for example). Fusion is like lighting a match to a bucket of gasoline. You need that input energy (the match), but what you get as a result is far more powerful. Fusion fuel is very energy dense. A thimbleful of liquid heavy-hydrogen fuel could produce as much energy as 20 tons of coal. Or, more realistically, one pick-up truck full of deuterium would release the energy equivalent of approximately 2 million tons of coal (21,000 rail car loads), or 1.3 million tons of oil (10 million barrels), or 30 tons of Uranium Oxide (1 rail car load). Clearly, with seawater as our energy source, our energy problems would be over forever! But there's a catch! In the sun, the energy to force nuclei together comes from the sun's immense internal temperatures, approaching 40,000,000 or more degrees at the center! In order to cause nuclei to fuse here on earth (and release their stored energy), they must either be heated to that temperature, or caused to move fast enough to simulate a correspondingly high temperature. That has been done already, more than 50 years ago. The energy to set off the fusion reaction was supplied by an atomic bomb, and the fusion reaction that resulted was called a 'hydrogen bomb'! But the energy release was all at once, and uncontrollable. While scientists were easily able to control atomic explosions, to create reasonably safe nuclear energy in atomic power plants, no such controlled reaction has yet been achieved for fusion. The reason lies in where the energy comes from. Nuclear fission of a plutonium nucleus already happens naturally ... we just help it along by allowing the reaction to proceed faster. Nuclear fusion, on the other hand, requires that the fuel nuclei be moving very fast, or be heated to very high temperatures. Scientists for the last 50 years have been trying to figure out how to do this, but so far the technology at our disposal is not equal to the task! Here are two different ways that we might achieve 'controlled' fusion, that are currently being explored in laboratories around the world. In order for fusion reactions to occur, the particles must be hot enough (temperature), in sufficient number (density) and well contained (confinement time). These simultaneous conditions are represented by a fourth state of matter known as plasma. In a plasma, electrons are stripped from their nuclei. A plasma, therefore, consists of charged particles, ions and electrons. There are two ways that are being explored for confining these hot plasmas - magnetic and inertial. Magnetic ConfinementEfforts to control fusion first relied on the principle of magnetic confinement, in which apowerful magnetic field traps a hot deuterium-tritium plasma long enough for fusion to begin. In November 1997, researchers exploiting the magnetic confinement approach created a fusion reaction that produced 65 percent as much energy as was fed into it to initiate the reaction. This milestone was achieved in England at the Joint European Torus, a tokamak facility--a doughnut-shaped vessel in which the plasma is magnetically confined. A commercial fusion reactor would have to produce far more energy than went into it to start or maintain the reaction. A 'Tokamak' reactor. Powerful magnets keep the charged nuclei moving in a circle, at high speeds. 'Tokamak' is a Russian acronym for 'toroidal magnetic chamber. This device was first developed by Russian scientists. A tokamak is a toroidal plasma confinement device, resembling a doughnut in shape. The plasma is confined not by the material walls but by magnetic fields. The reason for using magnetic confinement is twofold. First, no known material can withstand the hundred-million degree temperatures required for fusion. Second, keeping the plasma in a magnetic bottle insulates it well, making it easier to heat up. (Such reactors are inherently safe. If the plasma escapes, it immediately cools down, and the reaction stops!) Escaping neutrons and energy would heat a body of water; a steam turbine and generator would produce electricity. This magnetic confinement method for producing fusion is regarded by some scientists as the most promising one for future commercial energy sites. This stems from the way Magnetic Confinement fusion works, which allows for a sustained reaction and thus continuous energy production. Many 'tokamaks' are in operation currently, around the world, and more are planned for the future. But so far, none have been able to sustain the reaction for more than a few seconds ... the plasma leaks out. Improved magnet design and higher input power will perhaps allow these reactors in the future to maintain a fusion reaction indefinitely, producing copious amounts of power ... from seawater! Inertial ConfinementInertial confinement makes use of intense laser or electron beams to implode a fuel pellet. The pellet of deuterium/tritium fuel - a peppercorn-size fuel pellet - must be bombarded by two million joules, delivered in 4 nanoseconds. This is a power demand of 500 terawatts, and the equivalent of condensing up to ten hours' worth of electricity used by half a dozen homes into a fraction of a second! Lasers can do this. After many years of research, scientists have plans to build a very powerful laser that will produce at least as much energy from fusion as the laser delivers to the pellet, ... but that will still not come close to producing the several 100-fold greater energy required to power the laser itself. That goal requires a fusion energy output much greater than the energy put into the laser. Present laser technology is too expensive to go further, for now. A laser bombardment device. Here's how it's supposed to work. Many pulsed laser beams hit the fuel pellet simultaneously, causing the surface of the pellet to become a very hot plasma. This plasma expands inward, compressing the remaining deuterium and tritium so much that its temperature rises to the required 100,000,000 degrees. For about one tenth of a billionth of a second, there are the same conditions inside the pellet as those inside a star, ... and fusion takes place. To generate 1000 MW of electricity using such a reactor would require microexplosions of about six pellets in one second. This takes into consideration the inefficiency of the conversion from heat to electrical energy. In order to achieve these microexplosions, a chamber created to carry away the heat generated by the fusion would be built. A pellet would be shot into the center of the chamber and then the laser or particle accelerator would fire onto it, causing implosion and fusion. This would need to be repeated about six times a second. This method would probably work, but because it is not self-sustaining, (you have to keep feeding in the pellets), it is not very efficient. Most researchers now believe that magnetic containment devices will be the first ones to actually sustain a fusion reaction. Why Will Fusion Power Be Important? By the middle of the next century, the world's population will double, and energy demand willtriple. This will be due in large part to the industrialization and economic growth of developing nations. Continued use of fossil fuels (coal, oil and natural gas) will rapidly deplete these limited and localized natural resources. There is, perhaps, another 50-100 years supply of oil and natural gas, and enough coal for several hundred years. Burning these fossil fuels threatens to irreparably harm our environment. On the other hand, the deuterium in the earth's oceans is sufficient to fuel advanced fusion reactors for millions of years. The waste product from a deuterium-tritium fusion reactor isordinary harmless helium. Solar and renewable energy technologies will play a role in our energy future. Although they are inherently safe and feature an unlimited fuel supply, they are geographically limited, climate dependent and unable to meet the energy demands of a populous and industrialized world. Another option, nuclear fission, suffers from a negative public perception. High-level radioactive waste disposal, and the proliferation threat of weapons-grade nuclear materials, are major concerns. The fuel supply in this case, uranium, is large, but ultimately limited to several hundred years. The prospect of successful nuclear fusion technology, on the other hand, promises virtually unlimited energy, with very little danger. The radiation from a magnetic containment device is easily shielded, and (unlike uranium-fuelled fission power plants), if there is an accident and the magnetic containment is breached, the reaction immediately stops! Nuclear fusion indeed looks like it may be the power source of the future!

theory of relativity

Everything You Always Wanted toKnow About Einstein's Theory of Relativity...but were afraid to ask!

Strange things can happen when you move FAST...things you won't learn about in high school courses, and won't experience while driving down the road in your pick-up. But these things are still very real, and definitely WEIRD!

Light rays travel very quickly...they cover about 300,000 kilometres every SECOND. This is as fast as anything can travel; nothing can move as fast as light particles.
But if it were possible to build a very powerful vehicle that could move almost as fast as light...perhaps 200,000 km every second...then anyone observing this vehicle as it flashed past would notice some extremely peculiarthings happening to it.
The vehicle would appear shorter than normal, and in fact, it would be shorter. If the vehicle were ordinarily 3 metres long, it might now be only 2 metres in length.
If you were able to weigh the vehicle, you would discover that it weighed much more than normal. Anybody riding in it would weigh many times their normal weight.. However, the people in the vehicle would not FEEL any heavier, or any thinner. They would feel and look normal to themselves...but if they looked out the window, they would see the rest of the world moving by, and IT would appear to be shrunk.

If the vehicle were to move faster and faster, getting closer and closer to the speed of light, it and the people in it would continue to get thinner and thinner, while at the same time getting heavier and heavier!
These strange occurrences, as described by Albert Einstein, can actually be observed. It is not yet possible to build a vehicle that will go this fast, of course...the fastest spacecraft only cover about 15-20 kilometres in a second. But tiny particles called 'cosmic rays' that are given off by the sun...the ones that cause the Northern Lights when they hit earth's magnetic field...move almost as fast as light, and their mass can be measured. When they move that fast, their mass IS much heavier than normal.

A much more dramatic effect of moving fast is what happens to time. It seems that the faster you move, the more slowly time runs!
At normal, every-day speeds (airplane speed, for instance), the effect of 'time slowing down' is just barely measureable. You could fly nonstop around the world in an airplane, and because of your increase in speed, time would run slower for you. Everyone on the plane, all the watches and clocks, the plane itself...all would be a small fraction of a second YOUNGER than if they had not gone anywhere!
That experiment has been done. Want to live longer? Spend lots of time on high-speed planes, and time will move more slowly for you. You might live 2 seconds longer than you would have if you'd stayed on the ground.

Things get much more interesting if you fly off in a spacecraft that can go REALLY fast...perhaps 200.000 km per second. Now time is really slowing down. Suppose you and a friend are both exactly 16 years old. He stays on earth, but you go off for a trip in our very fast spacecraft.
Fifty years go by on earth. (It's a long way to the nearest stars!) You return to find your friend is now 65 years old.
You, however, have experienced a phenomenon known as time dilation. Time has been running more slowly for you, in the fast-moving spacecraft. According to you, the trip took only TEN years...and you are just 26 years old!

This effect would seem impossible...yet it has been demonstrated to be a fact. Once again, small particles can be observed and measured. Many are radioactive, which means they disintegrate with clockwork precision. The time it takes them to disintegrate can be accurately measured.
When these particles are accelerated to high ('relativistic') speeds as in our example above, they live longer before disintegrating!

You can visit our 'Twin Paradox' page to download a free program that illustrates and explains this amazing phenomenon.

It has been almost 100 years since these theories were first put forward by Einstein and others, and since then they have become accepted as fact by scientists world-wide. More evidence of their validity is also apparent from studies of objects in far distant space.

e=mc^2

Albert Einstein is perhaps the most famous scientist of this century. One of his most well-known accomplishments is the formula  Despite its familiarity, many people don't really understand what it means. We hope this explanation will help!

One of Einstein's great insights was to realize that matter and energy are really different forms of the same thing. Matter can be turned into energy, and energy into matter. For example, consider a simple hydrogen atom, basically composed of a single proton. This subatomic particle has a mass of 0.000 000 000 000 000 000 000 000 001 672 kgThis is a tiny mass indeed. But in everyday quantities of matter there are a lot of atoms! For instance, in one kilogram of pure water, the mass of hydrogen atoms amounts to just slightly more than 111 grams, or 0.111 kg. Einstein's formula tells us the amount of energy this mass would be equivalent to, if it were all suddenly turned into energy. It says that to find the energy, you multiply the mass by the square of the speed of light, this number being 300,000,000 meters per second (a very large number): = 0.111 x 300,000,000 x 300,000,000 = 10,000,000,000,000,000 Joules This is an incredible amount of energy! A Joule is not a large unit of energy ... one Joule is about the energy released when you drop a textbook to the floor. But the amount of energy in 30 grams of hydrogen atoms is equivalent to burning hundreds of thousands of gallons of gasoline! If you consider all the energy in the full kilogram of water, which also contains oxygen atoms, the total energy equivalent is close to 10 million gallons of gasoline! Can all this energy really be released? Has it ever been? The only way for ALL this energy to be released is for the kilogram of water to be totally annhilated. This process involves the complete destruction of matter, and occurs only when that matter meets an equal amount of antimatter ... a substance composed of mass with a negative charge. Antimatter does exist; it is observable as single subatomic particles in radioactive decay, and has been created in the laboratory. But it is rather short-lived (!), since it annihilates itself and an equal quantity of ordinary matter as soon as it encounters anything. For this reason, it has not yet been made in measurable quantities, so our kilogram of water can't be turned into energy by mixing it with 'antiwater'. At least, not yet. Another phenomenon peculiar to small elementary particles like protons is that they combine. A single proton forms the nucleus of a hydrogen atom. Two protons are found in the nucleus of a helium atom. This is how the elements are formed ... all the way up to the heaviest naturally occuring substance, uranium, which has 92 protons in its nucleus. It is possible to make two free protons (Hydrogen nuclei) come together to make the beginnings of a helium nucleus. This requires that the protons be hurled at each other at a very high speed. This process occurs in the sun, but can also be replicated on earth with lasers, magnets, or in the center of an atomic bomb. The process is called nuclear fusion. What makes it interesting is that when the two protons are forced to combine, they don't need as much of their energy (or mass). Two protons stuck together have less mass than two single separate protons! When the protons are forced together, this extra mass is released ... as energy! Typically this amounts to about 0.7% of the total mass, converted to an amount of energy predictable using the formula . Elements heavier than iron are unstable. Some of them are very unstable! This means that their nuclei, composed of many positively charged protons, which want to repel from each other, are liable to fall apart at any moment! We call atoms like this radioactive. Uranium, for example, is radioactive. Every second, many of the atoms in a chunk of uranium are falling apart. When this happens, the pieces, which are now new elements (with fewer protons) are LESS massive in total than the original uranium atoms. The extra mass disappears as energy ... again according to the formula ! This process is called nuclear fission. Both these nuclear reactions release a small portion of the mass involved as energy. Large amounts of energy! You are probably more familiar with their uses. Nuclear fusion is what powers a modern nuclear warhead. Nuclear fission (less powerful) is what happens in an atomic bomb (like the ones used against Japan in WWII), or in a nuclear power plant. Albert Einstein was able to see where an understanding of this formula would lead. Although peaceful by nature and politics, he helped write a letter to the President of the United States, urging him to fund research into the development of an atomic bomb ... before the Nazis or Japan developed their own first. The result was the Manhatten Project, which did in fact produce the first tangible evidence of  ... the atomic bomb!

aurora

An aurora (plural: auroras or aurorae) is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere. Aurora is classified as diffuse or discrete aurora. Most aurorae occur in a band known as the auroral zone^[1][2] which is typically 3° to 6° in latitudinal extent and at all local times or longitudes. The auroral zone is typically 10° to 20° from the magnetic pole defined by the axis of the Earth's magnetic dipole. During a geomagnetic storm, the auroral zone will expand to lower latitudes. The diffuse aurora is a featureless glow in the sky which may not be visible to the naked eye even on a dark night and defines the extent of the auroral zone. The discrete aurora are sharply defined features within the diffuse aurora which vary in brightness from just barely visible to the naked eye to bright enough to read a newspaper at night. Discrete aurorae are usually observed only in the night sky because they are not as bright as the sunlit sky. Aurorae occur occasionally poleward of the auroral zone as diffuse patches^[3] or arcs (polar cap arcs^[4]) which are generally invisible to the naked eye.

In northern latitudes, the effect is known as the aurora borealis (or the northern lights), named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, by Pierre Gassendi in 1621.^[5] Auroras seen near the magnetic pole may be high overhead, but from farther away, they illuminate the northern horizon as a greenish glow or sometimes a faint red, as if the Sun were rising from an unusual direction. Discrete aurorae often display magnetic field lines or curtain-like structures, and can change within seconds or glow unchanging for hours, most often in fluorescent green. The aurora borealis most often occurs near the equinoxes. The northern lights have had a number of names throughout history. The Cree call this phenomenon the "Dance of the Spirits". In Europe, in the Middle Ages, the auroras were commonly believed a sign from God (see Wilfried Schröder, Das Phänomen des Polarlichts, Darmstadt 1984).

Its southern counterpart, the aurora australis (or the southern lights), has almost identical features to the aurora borealis and changes simultaneously with changes in the northern auroral zone ^[6] and is visible from high southern latitudes in Antarctica, South America andAustralia.

Aurorae occur on other planets. Similar to the Earth's aurora, they are visible close to the planet's magnetic poles.

Modern style guides recommend that the names of meteorological phenomena, such as aurora borealis, be uncapitalized.^[7]

Contents   [show]

• 

  The aurora borealis shines above Bear Lake, Alaska.
 
• 

  Red and green aurora inFairbanks, Alaska.
 
• 

  Northern lights with very rare blue light overMoskosel, Lapland inSweden.
 
• 

  Northern lights over Malmesjaur, Moskosel, Lapland, Sweden.
 
• 

  Aurora & moon|Tromsø|
 
• 

  Aurora australis inAntarctica.
 
• 

  View of the aurora australis from theInternational Space Station.
 
• 

  False color DMSP image looking down from 850 km altitude showing discrete aurora (yellow) north of Scandinavia. Clouds and fog are blue.
 
• 

  Red color is caused by nitrogen being bombarded with radiation from a solar flare.

Video of the Aurora Australis taken by the crew ofExpedition 28 on board the International Space Station. This sequence of shots was taken September 17, 2011 from 17:22:27 to 17:45:12 GMT, on an ascending pass from south of Madagascar to just north of Australia over the Indian Ocean.

Video of the Aurora Australis taken by the crew of Expedition 28 on board the International Space Station. This sequence of shots was taken September 7, 2011 from 17:38:03 to 17:49:15 GMT, from the French Southern and Antarctic Lands in the South Indian Ocean to southern Australia.

Video of the Aurora Australis taken by the crew of Expedition 28 on board the International Space Station. This sequence of shots was taken September 11, 2011 from 13:45:06 to 14:01:51 GMT, from a descending pass near eastern Australia, rounding about to an ascending pass to the east of New Zealand.

[edit]Auroral mechanism

Auroras are result from emissions of photons in the Earth's upper atmosphere, above 80 km (50 mi), from ionized nitrogen atoms regaining an electron, and oxygen and nitrogen atoms returning from an excited state to ground state. They are ionized or excited by the collision of solar wind and magnetospheric particles being funneled down and accelerated along the Earth's magnetic field lines; excitation energy is lost by the emission of a photon of light, or by collision with another atom or molecule:

oxygen emissions

Green or brownish-red, depending on the amount of energy absorbed.

nitrogen emissions

Blue or red. Blue if the atom regains an electron after it has been ionized. Red if returning to ground state from an excited state.

Oxygen is unusual in terms of its return to ground state: it can take three quarters of a second to emit green light and up to two minutes to emit red. Collisions with other atoms or molecules will absorb the excitation energy and prevent emission. Because the very top of the atmosphere has a higher percentage of oxygen and is sparsely distributed such collisions are rare enough to allow time for oxygen to emit red. Collisions become more frequent progressing down into the atmosphere, so that red emissions do not have time to happen, and eventually even green light emissions are prevented.

This is why there is a colour differential with altitude; at high altitude oxygen red dominates, then oxygen green and nitrogen blue/red, then finally nitrogen blue/red when collisions prevent oxygen from emitting anything. Green is the most common of all auroras. Behind it is pink, a mixture of light green and red, followed by pure red, yellow (a mixture of red and green), and lastly pure blue.

Auroras are associated with the solar wind, a flow of ions continuously flowing outward from the Sun. The Earth's magnetic field traps these particles, many of which travel toward the poles where they are accelerated toward Earth. Collisions between these ions and atmospheric atoms and molecules cause energy releases in the form of auroras appearing in large circles around the poles. Auroras are more frequent and brighter during the intense phase of the solar cycle when coronal mass ejections increase the intensity of the solar wind.^[8]

A predominantly red aurora australis

[edit]Forms and magnetism

Aurora timelapse video

Northern lights over Calgary

Typically the aurora appears either as a diffuse glow or as "curtains" that approximately extend in the east-west direction. At some times, they form "quiet arcs"; at others ("active aurora"), they evolve and change constantly. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field lines, suggesting that auroras are shaped by Earth's magnetic field. Indeed, satellites show electrons to be guided by magnetic field lines, spiraling around them while moving towards Earth.

The similarity to curtains is often enhanced by folds called "striations". When the field line guiding a bright auroral patch leads to a point directly above the observer, the aurora may appear as a "corona" of diverging rays, an effect of perspective.

Although it was first mentioned by Ancient Greek explorer/geographer Pytheas, Hiorter andCelsius first described in 1741 evidence for magnetic control, namely, large magnetic fluctuations occurred whenever the aurora was observed overhead. This indicates (it was later realized) that large electric currents were associated with the aurora, flowing in the region where auroral light originated. Kristian Birkeland (1908)^[9] deduced that the currents flowed in the east-west directions along the auroral arc, and such currents, flowing from the dayside towards (approximately) midnight were later named "auroral electrojets" (see also Birkeland currents).

On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggering event for the onset of magnetospheric substorms.^[10] Two of the five probes, positioned approximately one third the distance to the moon, measured events suggesting a magnetic reconnection event 96 seconds prior to auroral intensification.^[11] Dr. Vassilis Angelopoulos of theUniversity of California, Los Angeles, the principal investigator for the THEMIS mission, claimed, "Our data show clearly and for the first time that magnetic reconnection is the trigger."^[12]

Still more evidence for a magnetic connection are the statistics of auroral observations. Elias Loomis (1860) and later in more detail Hermann Fritz (1881)^[13] and S. Tromholt (1882)^[14] established that the aurora appeared mainly in the "auroral zone", a ring-shaped region with a radius of approximately 2500 km around Earth's magnetic pole. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. The instantaneous distribution of auroras ("auroral oval"^[1][2]) is slightly different, centered about 3–5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest towards the equator around midnight. The aurora can be seen best at this time.

[edit]Solar wind and the magnetosphere

Schematic of Earth's magnetosphere

The Earth is constantly immersed in the solar wind, a rarefied flow of hot plasma (gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree heat of the Sun's outermost layer, the corona. The solar wind usually reaches Earth with a velocity around 400 km/s, density around 5 ions/cm³ and magnetic field intensity around 2–5 nT (nanoteslas; Earth's surface field is typically 30,000–50,000 nT). These are typical values. Duringmagnetic storms, in particular, flows can be several times faster; the interplanetary magnetic field(IMF) may also be much stronger.

The IMF originates on the Sun, related to the field of sunspots, and its field lines (lines of force) are dragged out by the solar wind. That alone would tend to line them up in the Sun-Earth direction, but the rotation of the Sun skews them (at Earth) by about 45 degrees, so that field lines passing Earth may actually start near the western edge ("limb") of the visible Sun.^[15]

Earth's magnetosphere is formed by the impact of the solar wind on the Earth's magnetic field. It forms an obstacle to the solar wind, diverting it, at an average distance of about 70,000 km (11 Earth radii or Re),^[16] forming a bow shock12,000 km to 15,000 km (1.9 to 2.4 Re) further upstream. The width of the magnetosphere abreast of Earth, is typically 190,000 km (30 Re), and on the night side a long "magnetotail" of stretched field lines extends to great distances (> 200 Re).

The magnetosphere is full of trapped plasma as the solar wind passes the Earth. The flow of plasma into the magnetosphere increases with increases in solar wind density and speed, with increase in the southward component of the IMF and with increases in turbulence in the solar wind flow.^[17] The flow pattern of magnetospheric plasma is from the magnetotail toward the Earth, around the Earth and back into the solar wind through the magnetopause on the day-side. In addition to moving perpendicular to the Earth's magnetic field, some magnetospheric plasma travel down along the Earth's magnetic field lines and lose energy to the atmosphere in the auroral zones. Magnetospheric electrons which are accelerated downward by field-aligned electric fields are responsible for the bright aurora features. The un-accelerated electrons and ions are responsible for the dim glow of the diffuse aurora.

[edit]Frequency of occurrence

North America

Eurasia

These NOAA maps of North America and Eurasia show the local midnight equatorward boundary of the aurora at different levels of geomagnetic activity. A Kp=3 corresponds to low levels of geomagnetic activity, while Kp=9 represents high levels.

Auroras are occasionally seen in temperate latitudes, when a magnetic storm temporarily grows the auroral oval. Large magnetic storms are most common during the peak of the eleven-year sunspot cycle or during the three years after that peak.^[18][19] However, within the auroral zone the likelihood of an aurora occurring depends mostly on the slant of interplanetary magnetic field (IMF) lines (the slant is known as B_z), being greater with southward slants.

Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes. It is not well understood why geomagnetic storms are tied to Earth's seasons while polar activity is not. But it is known that during spring and autumn, the interplanetary magnetic field and that of Earth link up. At themagnetopause, Earth's magnetic field points north. When B_z becomes large and negative (i.e., the IMF tilts south), it can partially cancel Earth's magnetic field at the point of contact. South-pointing B_z's open a door through which energy from the solar wind can reach Earth's inner magnetosphere.

The peaking of B_z during this time is a result of geometry. The IMF comes from the Sun and is carried outward with the solar wind. The rotation of the Sun causes the IMF to have a spiral shape called the Parker spiral. The southward (and northward) excursions of B_z are greatest during April and October, when Earth's magnetic dipole axis is most closely aligned with the Parker spiral.

However, B_z is not the only influence on geomagnetic activity. The Sun's rotation axis is tilted 8 degrees with respect to the plane of Earth's orbit. The solar wind blows more rapidly from the Sun's poles than from its equator, thus the average speed of particles buffeting Earth's magnetosphere waxes and wanes every six months. The solar wind speed is greatest – by about 50 km/s, on average – around 5 September and 5 March when Earth lies at its highest heliographic latitude.

Still, neither B_z nor the solar wind can fully explain the seasonal behavior of geomagnetic storms. Those factors together contribute only about one-third of the observed semiannual variations.

[edit]Auroral events of historical significance

The auroras that resulted from the "great geomagnetic storm" on both 28 August and 2 September 1859 are thought the most spectacular in recent recorded history. Balfour Stewart, in a paper^[20][21] to the Royal Society on 21 November 1861, described both auroral events as documented by a self-recording magnetograph at the Kew Observatory and established the connection between the 2 September 1859 auroral storm and the Carrington-Hodgson flare event when he observed that "it is not impossible to suppose that in this case our luminary was taken in the act." The second auroral event, which occurred on 2 September 1859 as a result of the exceptionally intense Carrington-Hodgson white light solar flare on 1 September 1859 produced auroras so widespread and extraordinarily brilliant that they were seen and reported in published scientific measurements, ships' logs and newspapers throughout the United States, Europe, Japan and Australia. It was reported by the New York Times^[22][23][24] that in Boston on Friday 2 September 1859 the aurora was "so brilliant that at about one o'clock ordinary print could be read by the light".^[23][25][26] One o'clock Boston time on Friday 2 September, would have been 6:00 GMT and the self-recording magnetograph at the Kew Observatory was recording the geomagnetic storm, which was then one hour old, at its full intensity. Between 1859 and 1862, Elias Loomis published a series of nine papers on the Great Auroral Exhibition of 1859 in the American Journal of Science where he collected world wide reports of the auroral event. The aurora is thought to have been produced by one of the most intensecoronal mass ejections in history, very near the maximum intensity that the Sun is thought to be capable of producing. It is also notable for the fact that it is the first time where the phenomena of auroral activity and electricity were unambiguously linked. This insight was made possible not only due to scientific magnetometer measurements of the era but also as a result of a significant portion of the 125,000 miles (201,000 km) of telegraph lines then in service being significantly disrupted for many hours throughout the storm. Some telegraph lines however seem to have been of the appropriate length and orientation to produce a sufficient geomagnetically induced current from theelectromagnetic field to allow for continued communication with the telegraph operators' power supplies switched off. The following conversation occurred between two operators of the American Telegraph Line between Boston and Portland, Maine, on the night of 2 September 1859 and reported in the Boston Traveler:

Boston operator (to Portland operator): "Please cut off your battery [power source] entirely for fifteen minutes."
Portland operator: "Will do so. It is now disconnected."
Boston: "Mine is disconnected, and we are working with the auroral current. How do you receive my writing?"
Portland: "Better than with our batteries on. – Current comes and goes gradually."
Boston: "My current is very strong at times, and we can work better without the batteries, as the aurora seems to neutralize and augment our batteries alternately, making current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble."
Portland: "Very well. Shall I go ahead with business?"
Boston: "Yes. Go ahead."

The conversation was carried on for around two hours using no battery power at all and working solely with the current induced by the aurora, and it was said that this was the first time on record that more than a word or two was transmitted in such manner.^[25] Such events led to the general conclusion that

The effect of the Aurora on the electric telegraph is generally to increase or diminish the electric current generated in working the wires. Sometimes it entirely neutralizes them, so that, in effect, no fluid is discoverable in them . The aurora borealis seems to be composed of a mass of electric matter, resembling in every respect, that generated by the electric galvanic battery. The currents from it change coming on the wires, and then disappear: the mass of the aurora rolls from the horizon to the zenith.^[27]

[edit]Origin

Aurora australis (11 September 2005) as captured by NASA's IMAGE satellite, digitally overlaid onto The Blue Marble composite image. An animation created using the same satellite data is also available.

The ultimate energy source of the aurora is the solar wind flowing past the Earth. The magnetosphere and solar wind consist of plasma (ionized gas), which conducts electricity. It is well known (since Michael Faraday's [1791 – 1867] work around 1830) that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts across (or is cut by), rather than along, the lines of the magnetic field, an electric current is said to be induced into that conductor and electrons will flow within it. The amount of current flow is dependent upon a) the rate of relative motion, b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the direction of flow is dependent upon the direction of relative motion.Dynamos make use of this basic process ("the dynamo effect"), any and all conductors, solid or otherwise are so affected including plasmas or other fluids.

In particular the solar wind and the magnetosphere are two electrically conducting fluids with such relative motion and should be able (in principle) to generate electric currents by "dynamo action", in the process also extracting energy from the flow of the solar wind. The process is hampered by the fact that plasmas conduct easily along magnetic field lines, but not so easily perpendicular to them. So it is important that a temporary magnetic connection be established between the field lines of the solar wind and those of the magnetosphere, by a process known as magnetic reconnection. It happens most easily with a southward slant of interplanetary field lines, because then field lines north of Earth approximately match the direction of field lines near the north magnetic pole (namely, into Earth), and similarly near the south magnetic pole. Indeed, active auroras (and related "substorms") are much more likely at such times. Electric currents originating in such way apparently give auroral electrons their energy. The magnetospheric plasma has an abundance of electrons: some are magnetically trapped, some reside in the magnetotail, and some exist in the upward extension of the ionosphere, which may extend (with diminishing density) some 25,000 km around Earth.

Bright auroras are generally associated with Birkeland currents (Schield et al., 1969;^[28] Zmuda and Armstrong, 1973^[29]) which flow down into the ionosphere on one side of the pole and out on the other. In between, some of the current connects directly through the ionospheric E layer (125 km); the rest ("region 2") detours, leaving again through field lines closer to the equator and closing through the "partial ring current" carried by magnetically trapped plasma. The ionosphere is an ohmic conductor, so such currents require a driving voltage, which some dynamo mechanism can supply. Electric field probes in orbit above the polar cap suggest voltages of the order of 40,000 volts, rising up to more than 200,000 volts during intense magnetic storms.

Ionospheric resistance has a complex nature, and leads to a secondary Hall current flow. By a strange twist of physics, the magnetic disturbance on the ground due to the main current almost cancels out, so most of the observed effect of auroras is due to a secondary current, the auroral electrojet. An auroral electrojet index (measured in nanotesla) is regularly derived from ground data and serves as a general measure of auroral activity.

However, ohmic resistance is not the only obstacle to current flow in this circuit. The convergence of magnetic field lines near Earth creates a "mirror effect" that turns back most of the down-flowing electrons (where currents flow upwards), inhibiting current-carrying capacity. To overcome this, part of the available voltage appears along the field line ("parallel to the field"), helping electrons overcome that obstacle by widening the bundle of trajectories reaching Earth; a similar "parallel potential" is used in "tandem mirror" plasma containment devices. A feature of such voltage is that it is concentrated near Earth (potential proportional to field intensity; Persson, 1963^[30]), and indeed, as deduced by Evans (1974) and confirmed by satellites, most auroral acceleration occurs below 10,000 km. Another indicator of parallel electric fields along field lines are beams of upwards flowing O+ ions observed on auroral field lines.

ISS Expedition 6 team. Lake Manicouaganis visible to the bottom left.

Some O+ ions ("conics") also seem accelerated in different ways by plasma processes associated with the aurora. These ions are accelerated by plasma waves, in directions mainly perpendicular to the field lines. They therefore start at their own "mirror points" and can travel only upwards. As they do so, the "mirror effect" transforms their directions of motion, from perpendicular to the line to lying on a cone around it, which gradually narrows down.

In addition, the aurora and associated currents produce a strong radio emission around 150 kHz known as auroral kilometric radiation (AKR, discovered in 1972). Ionospheric absorption makes AKR observable from space only.

These "parallel potentials" accelerate electrons to auroral energies and seem to be a major source of aurora. Other mechanisms have also been proposed, in particular, Alfvén waves, wave modes involving the magnetic field first noted by Hannes Alfvén (1942), which have been observed in the lab and in space. The question is however whether these waves might just be a different way of looking at the above process, because this approach does not point out a different energy source, and many plasma bulk phenomena can also be described in terms of Alfvén waves.

Wikinews has related news:Aurora Borealis caused by electrical space tornadoes

Other processes are also involved in the aurora, and much remains to be learned. Auroral electrons created by large geomagnetic storms often seem to have energies below 1 keV, and are stopped higher up, near 200 km. Such low energies excite mainly the red line of oxygen, so that often such auroras are red. On the other hand, positive ions also reach the ionosphere at such time, with energies of 20–30 keV, suggesting they might be an "overflow" along magnetic field lines of the copious "ring current" ions accelerated at such times, by processes different from the ones described above.

[edit]Sources and types

This article appears to contain unverifiable speculation and unjustified claims. Information must be verifiable and based on reliable published sources. Please remove unverified speculation from the article.

Understanding is very incomplete. There are three possible main sources:

1. Dynamo action with the solar wind flowing past Earth, possibly producing quiet auroral arcs ("directly driven" process). The circuit of the accelerating currents and their connection to the solar wind are uncertain.
2. Dynamo action involving plasma squeezed towards Earth by sudden convulsions of the magnetotail ("magnetic substorms"). Substorms tend to occur after prolonged spells (hours) during which the interplanetary magnetic field has an appreciable southward component, leading to a high rate of interconnection between its field lines and those of Earth. As a result the solar wind movesmagnetic flux (tubes of magnetic field lines, moving together with their resident plasma) from the day side of Earth to the magnetotail, widening the obstacle it presents to the solar wind flow and causing it to be squeezed harder. Ultimately the tail plasma is torn ("magnetic reconnection"); some blobs ("plasmoids") are squeezed tailwards and are carried away with the solar wind; others are squeezed towards Earth where their motion feeds large outbursts of aurora, mainly around midnight ("unloading process"). Geomagnetic storms have similar effects, but with greater vigor. The big difference is the addition of many particles to the plasma trapped around Earth, enhancing the "ring current" it carries. The resulting modification of Earth's field makes auroras visible at middle latitudes, on field lines much closer to the equator.
3. Satellite images of the aurora from above show a "ring of fire" along the auroral oval (see above), often widest at midnight. That is the "diffuse aurora", not distinct enough to be seen by the eye. It does not seem to be associated with acceleration by electric currents (although currents and their arcs may be embedded in it) but to be due to electrons leaking out of the magnetotail.

Any magnetic trapping is leaky—there always exists a bundle of directions ("loss cone") around the guiding magnetic field lines where particles are not trapped but escape. In the radiation belts of Earth, once particles on such trajectories are gone, new ones only replace them very slowly, leaving such directions nearly "empty". In the magnetotail, however, particle trajectories seem to be constantly reshuffled, probably when the particles cross the very weak field near the equator. As a result, the flow of electrons in all directions is nearly the same ("isotropic"), and that assures a steady supply of leaking electrons.

The energization of such electrons comes from magnetotail processes. The leakage of negative electrons does not leave the tail positively charged, because each leaked electron lost to the atmosphere is quickly replaced by a low energy electron drawn upwards from the ionosphere. Such replacement of "hot" electrons by "cold" ones is in complete accord with the 2nd law of thermodynamics.

Other types of auroras have been observed from space, e.g.^{[citation needed]} "poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. There are other interesting effects such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) has been observed around the two polar cusps, the "funnels" of field lines separating the ones that close on the day side of Earth from lines swept into the tail. The cusps allow a small amount of solar wind to reach the top of the atmosphere, producing an auroral glow.

• 

  Aurora borealis from the International Space Station.
 
• 

  Aurora during ageomagnetic storm that was most likely caused by a coronal mass ejectionfrom the Sun on 24 May 2010. Taken from the ISS.
 
• 

  Diffuse aurora observed by DE-1 satellite from low Earth orbit.

[edit]On other planets

Jupiter aurora. The bright spot at far left is the end of field line to Io; spots at bottom lead to Ganymede and Europa.

An aurora high above the northern part of Saturn. Image taken by the Cassini spacecraft. A movie showing images from 81 hours of observations of Saturn's aurora is also available.

Both Jupiter and Saturn have magnetic fields much stronger than Earth's (Jupiter's equatorial field strength is 4.3 gauss, compared to 0.3 gauss for Earth), and both have large radiation belts. Auroras have been observed on both, most clearly with the Hubble Space Telescope. Uranus andNeptune have also been observed to have auroras.^[31]

The auroras on the gas giants seem, like Earth's, to be powered by the solar wind. In addition, however, Jupiter's moons, especially Io, are powerful sources of auroras on Jupiter. These arise from electric currents along field lines ("field aligned currents"), generated by a dynamo mechanism due to the relative motion between the rotating planet and the moving moon. Io, which has active volcanism and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, studied since 1955. Auroras have also been observed on Io, Europa, and Ganymede themselves, e.g., using the Hubble Space Telescope. These Auroras have also been observed on Venus and Mars. Because Venus has no intrinsic (planetary) magnetic field, Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed across the full planetary disc. Venusian auroras are produced by the impact of electrons originating from the solar wind and precipitating in the night-side atmosphere. An aurora was also detected on Mars, on 14 August 2004, by the SPICAM instrument aboard Mars Express. The aurora was located at Terra Cimmeria, in the region of 177° East, 52° South. The total size of the emission region was about 30 km across, and possibly about 8 km high. By analyzing a map of crustal magnetic anomalies compiled with data from Mars Global Surveyor, scientists observed that the region of the emissions corresponded to an area where the strongest magnetic field is localized. This correlation indicates that the origin of the light emission was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.^[31][32]

[edit]History of aurora theories

In the past theories have been proposed to explain the phenomenon. These theories are now obsolete.

• Seneca speaks diffusely on auroras in the first book of his Naturales Quaestiones, drawing mainly from Aristoteles; he classifies them ("putei" or wells when they are circular and "rim a large hole in the sky", "pithaei" when they look like casks, "chasmata" from the same root of the English chasm, "pogoniae" when they are bearded, "cyparissae" when they look like cypresses), describes their manifold colors and asks himself whether they are above or below the clouds. He recalls that under Tiberius, an aurora formed above Ostia, so intense and so red that a cohort of the army, stationed nearby for fireman duty, galloped to the city.
• Benjamin Franklin theorized that the "mystery of the Northern Lights" was caused by a concentration of electrical charges in the polar regions intensified by the snow and other moisture.^[33]
• Auroral electrons come from beams emitted by the Sun. This was claimed around 1900 by Kristian Birkeland, whose experiments in a vacuum chamber with electron beams and magnetized spheres (miniature models of Earth or "terrellas") showed that such electrons would be guided towards the polar regions. Problems with this model included absence of aurora at the poles themselves, self-dispersal of such beams by their negative charge, and more recently, lack of any observational evidence in space.
• The aurora is the overflow of the radiation belt ("leaky bucket theory"). This was first disproved around 1962 by James Van Allen and co-workers, who showed that the high rate of energy dissipation by the aurora would quickly drain the radiation belt. Soon afterward, it became clear that most of the energy in trapped particles resided in positive ions, while auroral particles were almost always electrons, of relatively low energy.
• The aurora is produced by solar wind particles guided by Earth's field lines to the top of the atmosphere. This holds true for the cusp aurora, but outside the cusp, the solar wind has no direct access. In addition, the main energy in the solar wind resides in positive ions; electrons only have about 0.5 eV (electron volt), and while in the cusp this may be raised to 50–100 eV, that still falls short of auroral energies.
• After the Battle of Fredericksburg the lights could be seen from the battlefield that night. The Confederate army took it as a sign that God was on their side during the battle. It was very rare that one could see the Lights in Virginia.

[edit]Images

25-second exposure of the aurora australis from Amundsen-Scott S.P.S.

Images of auroras are significantly more common today due to the rise of use of digital camerasthat have high enough sensitivities.^[34] Film and digital exposure to auroral displays is fraught with difficulties, particularly if faithfulness of reproduction is an objective. Due to the different spectral energy present, and changing dynamically throughout the exposure, the results are somewhat unpredictable. Different layers of the film emulsion respond differently to lower light levels, and choice of film can be very important. Longer exposures aggregate the rapidly changing energy and often blanket the dynamic attribute of a display. Higher sensitivity creates issues with graininess.

David Malin pioneered multiple exposure using multiple filters for astronomical photography, recombining the images in the laboratory to recreate the visual display more accurately.^[35] For scientific research, proxies are often used, such as ultra-violet, and re-coloured to simulate the appearance to humans. Predictive techniques are also used, to indicate the extent of the display, a highly useful tool for aurora hunters.^[36] Terrestrial features often find their way into aurora images, making them more accessible and more likely to be published by the major websites.^[37] It is possible to take excellent images with standard film (using ISO ratings between 100 and 400) and a single-lens reflex camera with full aperture, a fast lens (f1.4 50 mm, for example), and exposures between 10 and 30 seconds, depending on the aurora's display strength.^[38]

Early work on the imaging of the auroras was done in 1949 by the University of Saskatchewan using the SCR-270 radar.

Red and green Auroras, Norway. Photo by Frank Olsen

[edit]In traditional and popular culture

In Bulfinch's Mythology from 1855 by Thomas Bulfinch there is the claim that in Norse mythology:

The Valkyrior are warlike virgins, mounted upon horses and armed with helmets and spears. /.../ When they ride forth on their errand, their armour sheds a strange flickering light, which flashes up over the northern skies, making what men call the "aurora borealis", or "Northern Lights".^[39]

While a striking notion, there is not a vast body of evidence in the Old Norse literature supporting this assertion. Although auroral activity is common over Scandinavia and Iceland today, it is possible that the Magnetic North Pole was considerably further away from this region during the centuries before the documentation of Norse mythology, thus explaining the lack of references.^[40]

The first Old Norse account of norðrljós is found in the Norwegian chronicle Konungs Skuggsjá from AD 1230. The chronicler has heard about this phenomenon from compatriots returning from Greenland, and he gives three possible explanations: that the ocean was surrounded by vast fires, that the sun flares could reach around the world to its night side, or that glaciers could store energy so that they eventually becamefluorescent.^[41]

In ancient Roman mythology, Aurora is the goddess of the dawn, renewing herself every morning to fly across the sky, announcing the arrival of the sun. The persona of Aurora the goddess has been incorporated in the writings of Shakespeare, Lord Tennyson and Thoreau.