Site Map

Guide to these web sites

      These web sites were written with several goals in mind.

      First, they try to provide non-scientists with clear explanations and explicit answers about physics and astronomy, in particular in those areas that concern space. That has been my own field of work. Many web pages exist about such subjects, but they often leave the reader no wiser, and at times, more confused. Here you may find straight answers, and the material is self-contained, you need no prior knowledge.

      Second, I tried to bring out interesting stories and connections, often from the history of science and of technology. Science has always been closely linked to culture and society, and the historical thread provides both continuity and human interest. For the non-scientist, especially those interested in space and its exploration, I have tried to open a window to a rich subculture with which society sees only dimly, often only getting a distorted view.

      And for students who might be getting their first look at science, as well as their teachers, I have tried to provide fresh material on physics, astronomy and earth sciences, with new content and added interest. Most of it is written at the high school level, though parts can be taught in middle school and others would fit undergraduate college. It is an open ended resource and includes extensions, links and references for the few who wish to explore at a higher level.

      I am a physicist, at the end of a long career in space research, but also familiar with the history of science and with many of the links between science, technology, culture and society (personal details at http://www.phy6.org/Education/wstern.html). I am well aware that most recent graduates from high school lack both the understanding of science and an interest in it. Reasons vary--e.g. rigid and formal curricula, lack of trained teachers, too much memorization, and too little new material--but whatever they might be, it seems high time to seek a more fruitful approach.


Home Pages

          The product of all this have been three book-size educational resources on the world-wide web. Below are the URLs of their home pages, each of which contains a linked table of contents, of 30-80 items.

        If you are using these files from a CD please omit the leading part of the URL, given here as http://www.phy6.org . For instance, to access the file given right below, got to "open page" (not "open location"), select your disk and then select stargaze/Sintro.htm .

        These web sites also have an alternative site, with the leading part of the URL replaced by http://www.phy6.org. You can also replace the leading part with http://www.istp.gsfc.nasa.gov, which is an alternative name of the NASA computer on which the files reside.

The URLs:

(1) "From Stargazers to Starships", home page
            http://www.phy6.org/stargaze/Sintro.htm
      The largest of the three, it covers elementary astronomy, Newtonian mechanics, the Sun and related physics and spaceflight. Also included are a Spanish translation, 42 lesson plans, a short but complete math course (algebra + trig), teachers' guides, glossary, timelines, questions by users and their answers, and more. The course is described in "Using Space to Teach Physics" in "The Physics Teacher", February 1999, p. 102.

Spanish home page:
            http://www.phy6.org/stargaze/Mintro.htm
Lesson plans home page:
            http://www.phy6.org/stargaze/Lintro.htm
Math course home page:
            http://www.phy6.org/stargaze/Smath.htm



(2) "The Great Magnet, the Earth", home page
            http://www.phy6.org/earthmag/demagint.htm

      This site provides a non-mathematical introduction to the magnetism of the Earth, the Sun, the planets and their environments, following a historical thread. It includes a Spanish translation (a French one will soon be added), guidance to teachers (including a detailed outline for use in earth sciences class), glossary, Q&A etc.

Spanish home page:
            http://www.phy6.org/earthmag/Mdmagint.htm



(3) "The Exploration of the Earth's Magnetosphere", home page
            http://www.phy6.org/Education/Intro.html
      This is a non-mathematical, self contained exposition of studies of the Earth's magnetic environment in space--my own area of interest. It too follows a historical thread and includes a Spanish translation (currently about 50% complete), a guide for teachers, glossary, timelines, a long history article (on a more technical level), an article "Birth of a Radiation Belt", Q&A and more. This material was described in the article "Space Physics for Poets" p. 38 in the January 1997 issue of "The Physics Teacher."

Spanish home page:
            http://www.phy6.org/Education/MIntro.htm



Lists of selected questions from users, with answers

In "Stargazers":
            http://www.phy6.org/stargaze/StarFAQs.htm

In "The Great Magnet":
            http://www.phy6.org/earthmag/magnQ&A1.htm

In "Exploration of the Earth's Magnetosphere": ,
            http://www.phy6.org/Education/FAQs1.html

If any of these is in your area of interest, please look it up. You may also copy the material the from compressed files which are provided. Comments and suggestions are welcome.

List of Specific Web Pages

      Each web collection may be used in one of two ways, as a single continuous course, or as individual modules and free-standing references. The list of web pages below is for those who prefer the second way and are interested in specific subjects. Each link is followed by a brief description of its contents.

      Even though it is only a partial list, it is quite long. Go ahead and explore, you may make unexpected discoveries! Spanish versions generally have similar names, but with a capital M replacing capital S as first letter; lesson plans start with letter L. Among the subjects covered:


  1.     The pole star
  2.     The sundial
  3.     Seasons of the year
  4.     The Moon
  5.     Latitude and longitude
  6.     The Calendar
  7.     The round earth
          and the story of Columbus
  8.     The distance to the horizon
  9.     The concept of parallax
  10.     The distance of the Moon

  11.     How the ancient Greeks
          guessed the size and
          distance of the Sun
  12.     Copernicus and Galileo
  13.     Kepler and his laws
  14.     Free fall due to gravity
  15.     Vectors
  16.     Energy
  17.     Newton's laws of motion
  18.     Mass, and its measurement
          in a weightless environment
  19.     Newton's 2nd law
  20.     Newton's 3rd law

  21.     How high voltages are created
          in the lab and in thunderstorms
  22.     Newton's theory of gravitation
  23.     Airplane flight
  24.     Centrifugal and centripetal forces
  25.     Motions in rotating frames of reference
  26.     The greenhouse effect
  27.     Thunderstorms and weather.
  28.     The Sun and sunspots
  29.     What is color?
  30.     Why is light an
          "electromagnetic wave"?

  31.     Energy sources and ultimate
          fate of the Sun and stars
  32.     Nuclear power stations
          and how they work.
  33.     Rockets
  34.     The story of Robert H. Goddard
  35.     Recent history of rocketry
          and spaceflight.
  36.     5 types of unmanned spacecraft.
  37.     Cannons that can reach space.
  38.     Nuclear power for spaceflight
  39.     Solar sails
  40.     Ion rockets

  41.     Lagrangian points--stable
          stations in space
  42.     How spacecraft gain speed
          from the gravity of planets
  1.     The story of the Pelton turbine.
  2.     Timeline of (basic) astronomy.
          Newtonian mechanics & spaceflight
  3.     Guidance to teachers on using
          the "Stargazers" material
  4.     "Stargazers" and National
          Science Education Standards
  5.     Inventory of concepts, stories...
  6.     Problems
  7.     A short course on the Earth's
          Magnetism in Earth Science Class
  8.     The early history of magnetism

  9.     Gilbert's "De Magnete" (1600).
  10.     Magnetism from Gilbert to 1820
  11.     How Oersted found electricity
          was linked to magnetism
  12.     Lodestones
  13.       Gauss and the 1st magnetic survey
  14.       Sunspots and magnetism
  15.     Fluid dynamos & Earth magnetism
  16.     Modern magnetometers & their uses
  17.     Pole reversals & moving continents
  18.     Magnetism in space around Earth

  19.     Magnetism of other planets
  20.     How Oersted found the link
          between electricity & magnetism.
  21.     Magnetic field lines
  22.     Electrons
  23.     Plasma
  24.     The fluorescent lamp
  25.     Positive ions
  26.     Energetic particles
  27.     The Geiger counter.
  28.     Cosmic rays

  29.     High energy particles
          in the Universe
  30.     The Sun, sunspots, their
          cycle & associated outbursts.
  31.     The Sun's Corona
  32.     The solar wind
  33.     Lagrangian points
  34.     Introduction to magnetism and
          the magnetosphere (summary)
  35.     Folding paper model of the
          Earth's magnetosphere
  36.     The polar aurora
  37.     Discovery of the radiation belt
  38.     Interplanetary field lines.

  39.     Magnetic storms and "Space Weather"
  40.     High energy particles from the Sun
  41.     The space tether experiment

(a) From Stargazers to Starships

  1.     The pole star
               
    http://www.phy6.org/stargaze/Spolaris.htm
    Tells about the northern polar constellations and about Alaska's state flag.            

  2.     The sundial
               
    http://www.phy6.org/stargaze/Sundial.htm
    Includes plans for a paper sundial, which can be copied from the web, xeroxed and cut out. Also has relevant calculations, formulas and links.

  3.     Seasons of the year
               
    http://www.phy6.org/stargaze/Sseason.htm
    Covers the length of the day and the angle of the Sun.
    More about that angle in
                http://www.phy6.org/stargaze/Sunangle.htm
    and about the variation of the distance from the Sun (possibly linked to ice ages) is in             http://www.phy6.org/stargaze/Sprecess.htm

  4.     The Moon
               
    http://www.phy6.org/stargaze/Smoon.htm
                http://www.phy6.org/stargaze/Smoon2.htm
    The 1st file covers the orbit and period of the Moon, its strange rotation and what causes it. The 2nd file covers the craters and appearance of the Moon, and the Apollo missions which landed there.

  5.     Latitude and longitude
               
    http://www.phy6.org/stargaze/Slatlong.htm
                http://www.phy6.org/stargaze/Snavigat.htm
    The first of these defines the subject, also discusses local time and the international date line. The second tells how latitude and longitude on Earth can be determined, illustrated by a story about the explorer Nansen.

  6.     The calendar
               
    http://www.phy6.org/stargaze/Scalend.htm
                http://www.phy6.org/stargaze/Sjewcale.htm
    The 1st web page covers Julian, Gregorian, Jewish (Metonic), Moslem and Maya calendars, with examples such as the October revolution (7 Nov) and George Washington's birthday (11 Feb, old style). The 2nd goes into details of the Jewish calendar and its Babylonian roots.

  7.     The round earth and the story of Columbus
               
    http://www.phy6.org/stargaze/Scolumb.htm
    The Greeks and Romans already knew the Earth was round, knew its size and noted India could be reached by sailing westward. Columbus actually misinterpreted his data!

  8.     The distance to the horizon
               
    http://www.phy6.org/stargaze/Shorizon.htm
    Derives the formula for that distance, using the Pythagoras theorem (see Spyth.htm), and tells the story of Pikes Peak.

  9.     The concept of parallax
               
    http://www.phy6.org/stargaze/Shorizon.ht
    Describes a simple parallax method for estimating distances outdoors, and how distances to stars were first measured.

  10.     The distance of the Moon
               
    http://www.phy6.org/stargaze/Shipprc2.htm
                http://www.phy6.org/stargaze/Shipparc.htm
    The first file describes the calculation by Greek astronomer Aristarchus, who around 250 BC used an eclipse of the Moon to deduce it was 60 Earth radii distant. The 2nd gives a derivation by Hipparchus, a century later, who confirmed the result using an eclipse of the Sun. That web page also applies his method to a very similar eclipse on 11 August 1999.

  11.     How the ancient Greeks guessed the size and distance of the Sun.
               
    http://www.phy6.org/stargaze/Sarist.htm
    The Greek astronomer Aristarchus concluded from observations that the Sun was 20 times more distant than the Moon, and 10 times larger in diameter than the Earth (actual numbers are around 400 and 100). Convinced that the Sun was much larger, he argued the Earth went around the Sun, not vice versa.

  12.     Copernicus and Galileo
               
    http://www.phy6.org/stargaze/Ssolsys.htm
    The riddle of retrograde motion of the planets, and the way it was addressed by Ptolemy and by Copernicus.

  13.     Kepler and his laws
               
    http://www.phy6.org/stargaze/Skeplaws.htm
    The story of Tycho and Kepler, and a basic description of Kepler's laws. Ellipses are introduced as conic sections, and a table shows how planetary orbits satisfy the 3rd law. Also contains the story of Tycho's supernova, observed recently from space in X-rays. An appended section on how actual distances in the solar system were measured:             http://www.phy6.org/stargaze/Sscale.htm

    The pages below contain more about the 1st and 2nd law, and about orbits.
                http://www.phy6.org/stargaze/Sellipse.htm
                http://www.phy6.org/stargaze/Skepl1st.htm
                http://www.phy6.org/stargaze/Skepl2nd.htm
                http://www.phy6.org/stargaze/Smotion.htm

  14.     Free fall due to gravity
               
    http://www.phy6.org/stargaze/Sfall.htm
    Introduces the student to accelerated motion and trajectories under the influence of gravity. Also has an experiment by Galileo and the story of the feather and hammer dropped together in vacuum on the Moon, by astronaut David Scott.

  15.     Vectors
               
    http://www.phy6.org/stargaze/Svector.htm
    Displacement as a vector--and continuing from there, velocity addition and resolution into components. For more on vectors, see "Airplane Flight" (item #23) below.

  16.     Energy
               
    http://www.phy6.org/stargaze/Senergy.htm
    An intuitive approach to energy, with many examples of conversion from one form to another. Energy is like money--it pays for every physical every process, and heat is the "soft currency" of the energy world.

  17.     Newton's laws of motion
               
    http://www.phy6.org/stargaze/Snewton.htm
    The first in a number of web pages giving a careful and gradual development of Newton's laws, starting with the concepts of force and inertia.

  18.     Mass, and the way it was measured in weightless environment
               
    http://www.phy6.org/stargaze/Smass.htm
                http://www.phy6.org/stargaze/Sskylab.htm
                http://www.phy6.org/stargaze/Smasscom.htm
    Developing the concept of mass, carefully distinguished from weight. To illustrate the distinction, it is shown how mass was measured in 1973 in the "weightless" environment of space station "Skylab." The 3rd file describes a similar measurement ("inertial balance") which can be performed with simple equipment.

  19.     Newton's 2nd law
               
    http://www.phy6.org/stargaze/Snewt2nd.htm
    Illustrated by the calculation of the acceleration of a rocket, at launch and at burnout.

  20.     Newton's 3rd law
               
    http://www.phy6.org/stargaze/Snewton3.htm
    Clearly distinguishes static reaction (not involving the 3rd law) from actual examples of the 3rd law--including the recoil of a gun and of fire hose, the garden sprinkler, jumping off a boat and balancing a bicycle. Ends with Mach's formulation of Newton's laws. Another web page introduces momentum and its conservation:
                http://www.phy6.org/stargaze/Smoment.htm

  21.     How high voltages are created in the lab and in thunderstorms:
               
    http://www.phy6.org/stargaze/Svandgrf.htm
    Uses the Van de Graaff generator to illustrate of the performance of work against electric forces and the conservation of energy. The high voltages that cause lightning have a somewhat similar origin.

  22.     Newton's theory of universal gravitation
               
    http://www.phy6.org/stargaze/Sgravity.htm
    Cites the original story of Newton's apple, then shows how Newton used the motion of the Moon to confirm his guess.

  23.     Airplane flight
               
    http://www.phy6.org/stargaze/Sflight.htm
    An introduction to airplane flight, illustrating the use of vector addition in the sweep-back (or sweep-forward) of wings and in the design of propellers.

  24.     Centrifugal and centripetal forces
               
    http://www.phy6.org/stargaze/Sframes2.htm
                http://www.phy6.org/stargaze/Sframes2.htm
                http://www.phy6.org/stargaze/Sframes3.htm
    A careful derivation, stressing the distinction between the two. The 1st unit develops the concept of centripetal force, using the theorem of Pythagoras. The other two introduce, first accelerated frames of reference, then rotating ones (in which centrifugal forces are evident).

  25.     Motions in rotating frames of reference
               
    http://www.phy6.org/stargaze/Srotfram.htm
    Develops the concept of "weightlessness" and discusses the Coriolis force, as illustrated in the swirling of hurricanes and (by popular misconception) of water draining from a sink.

  26.     The greenhouse effect
               
    http://www.phy6.org/stargaze/Sun1lite.htm
          The flow of energy is traced from sunlight to Earth and back to space. Any light not reflected (e.g. from clouds) heats the ground and must be re-radiated into space as infra-red light. The atmosphere transports a large part of that heat, which produces our weather, ultimately re-radiating that energy to space, too. "Greenhouse gases" that absorb infra red--e.g. water vapor, carbon dioxide, methane and ozone--complicate the process.

  27.     Thunderstorms and weather.
               
    http://www.phy6.org/stargaze/Sweather.htm
          More about the transport of heat from the ground into space, and the air motions it creates. A significant amount of solar heat evaporates water, allowing air to store appreciable energy as humidity. In a thunderstorm that energy is released in a rather spectacular fashion, driving a flow of air vertically upward.

  28.     The Sun and sunspots
               
    http://www.phy6.org/stargaze/Sun3mag.htm
          Sunspots are intensely magnetic areas on the Sun. Since the Sun consists of glowing gas, their magnetism cannot be permanent, but must come from electric currents--by a process which Oersted discovered in 1820, described here. Also described is the discovery around 1843 of the 11-year sunspot cycle, not by a professional astronomer but by a persistent amateur, Heinrich Schwabe. Sunspot magnetism is responsible for some interesting abrupt energy releases, leading to "magnetic storms" at Earth,

  29.     What is color?
               
    http://www.phy6.org/stargaze/Sun4spec.htm
          To us, color is the combination of responses of 3 types of sensors in the eye. To laboratory instruments, each frequency has its distinct color. Hot solids radiate a continuous distribution of colors, but hot gases emit narrow color ranges, which can identify them. An unknown color found in sunlight was assigned to a new unknown element "helium" (helios=sun), later found on Earth as well.

  30.     What makes light an "electromagnetic wave"?
               
    http://www.phy6.org/stargaze/Sun5wave.htm
          A quick, somewhat simplified introduction to a complex subject. Oersted showed electric currents created magnetism, and Faraday a little later showed that changing magnetism could create electric currents. So a wave-like disturbance, alternating between electric and magnetic effects, should be able to spread in empty space, but only IF space could carry an electric current! Maxwell showed that a small addition to the equations of electricity allowed such currents to flow, with the wave spreading with the speed of light. Did such waves exist? Yes, as Heinrich Hertz proved by creating radio waves in his lab. Then came quantum theory, showing that while light might spread as a wave, it gave up its energy in particle-like chunks, named photons.

  31.     The energy sources and ultimate fate of the Sun and of stars
               
    http://www.phy6.org/stargaze/Sun7enrg.htm
          Describes the principles of nuclear fusion which supplies the energy of the Sun, mostly by converting hydrogen to helium in the Sun's core. Other nuclear processes can add moderate amounts of energy, but ultimately any star runs out of nuclear fuel and can produce heat only by collapsing and releasing gravitational energy. The length of the star's normal "life," as well as the end product--white dwarf, neutron star or black hole--depend on its size.

  32.     Nuclear power stations and how they work.
               
    http://www.phy6.org/stargaze/Snuclear.htm
          Students who in section #31 learned the principles of nuclear physics can apply them here to nuclear fission and to the operation of power-producing nuclear reactors. Also describes a few of the better-known mishaps of the nuclear industry.

  33.     Rockets
               
    http://www.phy6.org/stargaze/Srocket.htm
          Rockets depend on Newton's 3rd law: they move forward by the reaction of a very fast jet of hot gas, ejected backwards. Their operation can also be understood from the conservation of momentum, which leads to the observation that (in the absence of other participants) the center of gravity of rocket plus jet always stays in the same place.

  34.     The story of Robert H. Goddard
               
    http://www.phy6.org/stargaze/Sgoddard.htm
          Robert Goddard was a creative dreamer, whose vision of spaceflight first took shape as he sat among the branches of a cherry tree in 1899, at age 17. In later experiments he found that commercial rockets had only a 2% efficiency, but he raised it to 60% (and made space flight possible!) by applying a nozzle design developed for steam turbines. He flew his first liquid-fuel rocket in 1926, and the rest is history.

  35.     Recent history of rocketry and spaceflight.
               
    http://www.phy6.org/stargaze/Srockhis.htm
                http://www.phy6.org/stargaze/Spacefly.htm
          A historical overview of the development of rockets--first by German amateurs, later by the German military and by US pioneers at the "Jet Propulsion Lab," then after WW II in the missile race between the US and the Soviet Union, which turned into the space race after the launch of Sputnik 1.

  36.         Five types of unmanned spacecraft.
               
    http://www.phy6.org/stargaze/Satell2.htm
                http://www.phy6.org/stargaze/Satell3.htm
                http://www.phy6.org/stargaze/Satell4.htm
                http://www.phy6.org/stargaze/Satell5.htm
                http://www.phy6.org/stargaze/Satell6.htm
          Unmanned spacecraft can be divided into those that look up into space (e.g. observe the stars), those that look down and observe Earth, those that explore the local environment in space, those designed for practical and commercial uses (such as communications), and those that explore the distant planets and space regions. Examples of each type are described, with links to additional relevant web sites.

  37.     Designing cannons to fire into space
               
    http://www.phy6.org/stargaze/Smartlet.htm
                http://www.phy6.org/stargaze/SSHARP.htm
    Cannons have been built to send probes up to 80 miles above ground, and in principle it is possible to reach even further. Some clever tricks help, such as using compressed hydrogen gas to propel the probes, but the acceleration is fierce.

  38.     Nuclear power for spaceflight
               
    http://www.phy6.org/stargaze/Snucfly.htm
    Nuclear processes provide a very concentrated source of energy, but harnessing them for spaceflight is difficult. Even nuclear bombs were once seriously considered, in "Project Orion."

  39.     Solar sails
               
    http://www.phy6.org/stargaze/Solsail.htm
          Once a spacecraft has reached a stable orbit, it can in principle gain further energy from the pressure of sunlight, bounced off large "solar sails." The challenge is to design sails that are sufficiently light, rigid and durable.

  40.     Ion rockets
               
    http://www.phy6.org/stargaze/Sionrock.htm
          Another way for an orbiting spacecraft to gain more speed is to collect solar energy and use it to power an electric rocket engine, accelerating gas stored on board. The energy given to that gas is greater than what it could get from stored chemical energy (as in conventional rocket fuel). An ion engine aboard "Deep Space 1" has successfully given it a boost in interplanetary space.

  41.     Lagrangian points--stable stations in space
    .            
    http://www.phy6.org/stargaze/Slagrang.htm
                http://www.phy6.org/stargaze/Slagrng2.htm
                http://www.phy6.org/stargaze/Slagrng3.htm
          Spacecraft at these points maintain fixed positions relative to the moving Earth. The L1 point, sunward of us at about 4 times the distance of the Moon, has been used by several NASA spacecraft. The L2 point, equally far on the nightward side, is where the "Microwave Anisotropy Probe" (launched 6.30.2001) and the "Next Generation Space Telescope" are to be placed, and L4 and L5 also have interesting uses. Calculations of these equilibria are given here--no calculus, but a great deal of algebra!

  42.     How spacecraft gain speed from the gravity of planets.
               
    http://www.phy6.org/stargaze/Stostars.htm
    Spacecraft exploring the planets often use them (or our Moon) to gain extra energy, in the same way a ping-pong ball gains a surprising amount of energy from the paddle. And in the far future, may burned-out stars be the best means of reaching truly distant space?

  43.     The story of the Pelton turbine.
               
    http://www.phy6.org/stargaze/Spelton.htm
          Lester Pelton was an inventor during the California gold rush. The highly efficient water turbine which he invented is based on a principle quite similar to that by which space probes interact with moving planets.

  44.     Timeline of (basic) astronomy, Newtonian mechanics and spaceflight
               
    http://www.phy6.org/stargaze/Stimeln2.htm
          A chronology of basic astronomy, mechanics and spaceflight, keyed to the "Stargazers" text. All entries are in red, embedded in a timeline (black print) of the history of humanity and its technology.

    EDITED TO HERE

    PLEASE NOTE: The "Stargazer" files below are currently not available in the Spanish translation, and neither are the lesson plans

  45.     Guidance to teachers on using the "Stargazers" material
               
    http://www.phy6.org/stargaze/Steacher.htm
    Describes (1) the different parts of the collection (2) Suggested student projects and the pages on which each might be based (3) The pedagogical ideas underlying this material (4) An inventory of what is covered.

  46.         "Stargazers" and National Science Education Standards.
               
    http://www.phy6.org/stargaze/Standrds.htm
    Point-by-point description of the way "Stargazers" adheres to national standards.

  47.     Inventory of concepts, stories...
               
    http://www.phy6.org/stargaze/Sinvent.htm
    Section-by-section listing of (1) Concepts covered (2) Calculations and formulas (3) Stories, extensions and examples

  48.     Problems
               
    http://www.phy6.org/stargaze/Sproblem.htm
                http://www.phy6.org/stargaze/Sproblm2.htm
    Two sets of problems related to the text (currently numbering 72). Answers will be provided by regular mail, to teachers writing on their school's letterhead. Problems are at different levels, and many require "figuring out" rather than straight-forward application of formulas. They are also suitable for classroom examples. The files below contain problems related to the "Math Refresher" and cover algebra and trigonometry, respectively:
                http://www.phy6.org/stargaze/Salgeb1A.htm
                http://www.phy6.org/stargaze/Strig6.htm

    (b) The Great Magnet, the Earth

            This is a different kind of site, following the historical timeline of the study of the Earth's magnetic field. In schools its most appropriate application may be a 3-4 week course on the Earth's magnetism, described in the next item below. Such a course would also introduce some fundamental concepts of electromagnetism, the layers of the solid Earth and the experimental foundations of plate tectonics (once known as "continental drift").

  49.     A short course on the Earth's Magnetism in Earth Science Class
               
    http://www.phy6.org/earthmag/NSTA1A.htm
                http://www.phy6.org/earthmag/NSTA1B.htm
                http://www.phy6.org/earthmag/NSTA1C.htm
    This was presented as a 1-hour invited talk before a meeting of the Natl. Science Teachers Association.

            This site was first assembled to mark the 400th anniversary of William Gilbert's book "De Magnete" ("On the Magnet"), which appeared in London in 1600 and which started a new era in science. The first 6 web pages are connected with that anniversary and describe some interesting early applications of the scientific method.

  50.     The early history of magnetism
               
    http://www.phy6.org/earthmag/upto1600.htm
    The discovery of magnetism in ancient Greece and independently in China, where around 1000 AD the magnetic compass was invented. The ingenious experiment by which Robert Norman in 1581 showed that the magnetic force on the compass needle was not horizontal.

  51.     William Gilbert's book "De Magnete" (1600).
               
    http://www.phy6.org/earthmag/DMGRev2.htm
                http://www.phy6.org/earthmag/demagrev.htm
                http://www.phy6.org/earthmag/demagadd.htm
    Two reviews of the book, and some additional details.

                http://www.phy6.org/earthmag/inducemg.htm
    One of Gilbert's experiments, which can be duplicated with simple equipment.
                http://www.phy6.org/earthmag/lond1600.htm
    London in 1600--the city of William Gilbert, also of Queen Elizabeth and Shakespeare

  52.     Magnetism from Gilbert to 1820
               
    http://www.phy6.org/earthmag/to1820.htm
    Edmond Halley, who gave his name to a famous comet, also led the expedition which produced the first magnetic chart. Cameo appearances in this section by Anders Celsius (of the centigrade temperature scale) and by Jonathan Swift.

  53.     The link between electricity and magnetism, and how it was found
               
    http://www.phy6.org/earthmag/oersted.htm
    Electricity and magnetism used to be two separate fields, up to an accidental discovery in 1820 by a Danish professor, H.C. Oersted. He could not make sense of what he observed. Includes easy table-top duplication of his experiment.

  54.     Lodestones
               
    http://www.phy6.org/earthmag/lodestn.htm
    If natural stone-magnets did not exist, humanity might not have discovered the compass as early as it did--and not America as well, maybe. An accident of nature, they are probably created by lightning.

  55.     Gauss and the first magnetic survey
               
    http://www.phy6.org/earthmag/gauss.htm
    When a great mathematician decided to investigate magnetism, it led to the first global magnetic surveys (also the first telegraph). His analysis method is still used, and it has revealed that the north-south magnetic polarity of the earth has been getting steadily weaker, at 5% per century or faster.

  56.     The Sun's magnetism and the sunspot cycle.
               
    http://www.phy6.org/earthmag/sunspots.htm
    This is covered and described in item #28 above, and also in
                http://www.phy6.org/Education/whsun.html
    and its linked files
                http://www.phy6.org/Education/whschwab.html
                http://www.phy6.org/Education/whcarr.html

  57.     Fluid dynamos and the magnetism of the Earth
               
    http://www.phy6.org/earthmag/dynamos.htm
                http://www.phy6.org/earthmag/dynamos2.htm
    Michael Faraday, inventor (in a way) of the electric dynamo and motor, also showed that the flow of electrically conducting fluids in the presence of magnetism could produce electric currents... which could amplify that magnetism, perhaps even start it. Since the Sun consisted of glowing gas, that is how the magnetism of sunspots must originate--which led other scientists to seek a similar process in the Earth's core, responsible for the magnetism of Earth.

  58.     Modern magnetometers and their use in research.
               
    http://www.phy6.org/earthmag/magmeter.htm
    For a long time magnetism was measured by magnetic needles suspended on fine strings, but later electronic magnetometers were developed; one type, the fluxgate, is described here. They are the obvious choice aboard spacecraft, but also have many other uses, including an ingenious experiment by Dr. David Cohen which shed new light on damage due to cigarette smoking.

  59.     Magnetic Reversals and moving continents
               
    http://www.phy6.org/earthmag/reversal.htm
                http://www.phy6.org/earthmag/magnQ&A1.htm#q6
    When molten lava solidifies, it records the direction of the surrounding magnetic field. For recent lava flows, this is always north-south--but ancient lava sometimes records reversed fields. That was explained by dynamo theory (#57 above), band has confirmed the slow motion of continents, e.g. the drifting-apart of Europe and America, advocated by Wegener in the early 1900s and rejected by his contemporaries.

  60.     The magnetic space environment around Earth
               
    http://www.phy6.org/earthmag/magspher.htm
    The Earth's magnetic influence extends into space around it, confining radiation belts, producing the polar aurora ("northern lights") and manifesting "magnetic storms" prompted by events on the Sun.

  61.     Magnetism of other planets.
               
    http://www.phy6.org/earthmag/planetmg.htm
    also             http://www.phy6.org/Education/wotherms.html
    The Earth is not the only magnetic planet: space probes have shown that the giant gas planets--Jupiter, Saturn, Uranus and Neptune--all have even stronger magnetism. The magnetic field and radiation belt of Jupiter are particularly powerful, and fields of other planets have their own peculiarities. Venus, a near twin of Earth is non-magnetic, but not so tiny Mercury. Mars has some surface magnetization, and our Moon does too, though it is not nearly as strong.

    (c) Exploration of the Earth's Magnetosphere

          This educational site was placed on the web ahead of the other two, with a somewhat different goal--to tell interested non-scientists what space research was like, or at least, one of its important areas. It is non-mathematical and self-contained, but much of its subject matter goes beyond the usual school curriculum.

            However... to understand these subjects, users were given a quick introduction to magnetism, electrons and ions, plasmas and other concepts of physics, as well as to the Sun and some other astronomical subjects, all of which may be relevant to the high school curriculum. Among these:

  62.     The link between electricity and magnetism and its discovery by Oersted
               
    http://www.phy6.org/Education/wmfield.html
                http://www.phy6.org/Education/whmfield.html
    This material is similar to #53 above and includes the same table-top experiment.

  63.     Magnetic field lines (or "lines of force")
               
    http://www.phy6.org/Education/wfldline.html
                http://www.phy6.org/Education/whfldlns.html
    Explains how magnetic forces can be described by a map of field lines, then goes on to tell the story of Michael Faraday, and the way he and James Maxwell introduced the concept of magnetic "fields." That in its turn led to the idea that light might be part of a larger family of "electromagnetic waves," a concept described in
                http://www.phy6.org/Education/wemwaves.html

  64.     Electrons
               
    http://www.phy6.org/Education/welect.html
                http://www.phy6.org/Education/whelect.html
    All atoms contain tiny particles charged with negative electricity. Many clues existed to their existence before J.J. Thomson discovered them in 1897, including the "Edison effect" described here. Had early scientists known about electrons, our convention of naming "positive" and negative" electric charges might have been reversed. However, that choice was arbitrarily made by Ben Franklin some 150 years earlier:             http://www.phy6.org/Education/woppos.html

  65.     Plasma
               
    http://www.phy6.org/Education/wplasma.html
                http://www.phy6.org/Education/whplasma.html
    Plasma is a gas hot enough for electrons to be torn off its atoms, making it a conductor of electricity. Much of space is filled with plasma, fluorescent lights also use it (next item below), and four major areas of science and technology involve plasmas. The term, originally applied to blood fluid, was given this added meaning in1927 by Irving Langmuir (as quoted here).

  66.     The fluorescent lamp: a plasma you can use.
               
    http://www.phy6.org/Education/wfluor.html
    Anyone who believes that Ohm's law always governs the conduction of electricity will be surprised by the greedy behavior of plasmas. The wiring of fluorescent light tubes highlights not only that behavior but also the storage of energy in magnetic fields.

  67.     Positive ions
               
    http://www.phy6.org/Education/wposion.html
                http://www.phy6.org/Education/whposion.html
    When one or more electrons are torn off an atom, what remains is known as a positive ion. Ions are important in radioactivity, in space and even in chemistry. And did you know that practically all helium atoms used for filling balloons started out as "alpha particles," very energetic ions emitted by radioactive heavy elements?

  68.     Energetic particles
               
    http://www.phy6.org/Education/wenpart1.html
    All about the energy unit "electron volt" (ev) in which particle energies are measured. Particle energies found in nature cover a huge range, from 0.03 ev (molecules at room temperature) to billions and trillions of ev, observed in the cosmic radiation (#70 below).

  69.     The Geiger counter.
               
    http://www.phy6.org/Education/wgeiger.html
    Among the earliest and most versatile radiation detectors, one version of which discovered the radiation belt of Earth.

  70.     Cosmic rays
               
    http://www.phy6.org/Education/wcosray.html
    A thin drizzle of ions with very high energies, constantly showering the Earth and arriving evenly from all directions. Astronomers believe they are produced by supernovas--but many open questions remain.

  71.     High energy particles in the Universe
               
    http://www.phy6.org/Education/wenpart2.html
    Cosmic rays (see #70 above) are but one indication that the universe is constantly channeling a surprising amount of energy to an "elite" of particles whose energy share is far above the average. Radio waves, gamma ray bursts, X-rays and other emissions all bear witness.

  72.     The Sun, its sunspots, sunspot cycle and associated outbursts.
               
    http://www.phy6.org/Education/wsun.html
                http://www.phy6.org/Education/whsun.html"
    In the main, the Sun is a giant furnace, constantly releasing nuclear energy which it radiates to space, making possible life on Earth. Its surface, however, also has magnetic features such as sunspots, and intricate phenomena. See also items #28 and #56 above. The famous sunspot cycle was accidentally discovered by an amateur seeking an elusive planet. His report is given here:             http://www.phy6.org/Education/whschwab.html
    The discovery of explosive events near sunspots, by Richard Carrington in 1859:             http://www.phy6.org/Education/whcarr.html

  73.     The Sun's Corona
               
    http://www.phy6.org/Education/wcorona.html
    The further one sits from a furnace, the cooler the environment--but not near the Sun, where the outer layer, the corona, reaches 1,000,000 deg. centigrade or more, far hotter than the visible surface below it. The reason is still a mystery, but the effects are quite evident (see next item below).

  74.     The solar wind
               
    http://www.phy6.org/Education/wsolwind.html
                http://www.phy6.org/Education/whsolwi.html
    The corona is too hot for the sun's gravity to hold onto it, and so it constantly expands in all directions as a "solar wind" at 400 km/sec (or about a million mph). This flow extends beyond the outer planets, on the way cooping up planetary magnetic fields (our own included) and also affecting comet tails.

  75.     Lagrangian points
               
    http://www.phy6.org/Education/wlagran.html
    These equilibrium points in the Earth-Sun system (they also exist in the Earth-Moon system) have interesting uses. See item #41 above.

    ...and in addition, about the Earth's magnetosphere:

  76.     Introduction to magnetism and the magnetosphere (summary file)
               
    http://www.phy6.org/Education/Imagnet.html
    The first of 8 files which together summarize this web site and link to more detailed web pages.

  77.     Folding paper model of the Earth's magnetosphere
               
    http://www.phy6.org/Education/wfold.html
    A plan for creating a small 3-dimensional paper model, of the Earth's magnetosphere and its regions. It can be downloaded, printed, xeroxed and even colored,
  78.     The polar aurora
               
    http://www.phy6.org/Education/waurora1.html
                http://www.phy6.org/Education/whaur1.html
    The "northern lights" seen frequently in Canada and Alaska (but rarely further away from the poles) are produced when fast electrons, guided by magnetic field lines, hit the high atmosphere. The electrons originate in the distant magnetosphere and are related to electric currents and energy releases. The two pages below give some details: more can be found in other parts of "Exploration of the Earth's Magnetosphere."             http://www.phy6.org/Education/wimage.html
                http://www.phy6.org/Education/waurora2.html

  79.     Discovery of the radiation belt
               
    http://www.phy6.org/Education/wexp13.html
    The discovery of the radiation belt in the spring of 1958 was an unexpected achievement of the early US space program. The story--and the plot of data from Explorer 3, which gave away the secret--can be found here.

  80.     The shape of interplanetary field lines.
               
    http://www.phy6.org/Education/wimfproj.html
    A graphic exercise illustrating the way the solar wind drags out solar magnetic field lines. The solar wind moves out radially, but field lines stay linked to their starting points on the Sun and therefore form tighter and still tighter spirals. Protons from an active solar event in 1998, guided by field lines, took 6 months and 10 circuits around the Sun to reach Voyager 2; they barely beat the much slower solar wind, moving outwards along a straight path.

  81.     Magnetic storms and "Space Weather"
               
    http://www.phy6.org/Education/wmagstrm.html
                http://www.phy6.org/Education//weather.html
    When plasma clouds led by shock fronts hit the Earth's magnetosphere, fresh particles are accelerated and radiation belts grow stronger, in a disturbance which may last 1-4 days. Satellites may sustain damage, and momentary overloads may hit the power grid. For an interesting 1991 event of this sort, see "Birth of a Radiation Belt" at             http://www.phy6.org/Education/wbirthrb.html

  82.     High energy particles emitted by the Sun
               
    http://www.phy6.org/Education/wsolparthtml
    Outbursts on the Sun--associated with sunspot activity--sometimes accelerate ions and electrons to quite high energies.

  83.     The space tether experiment (see also #57 on the "dynamo effect")
               
    http://www.phy6.org/Education/wtether.html
    A 20 kilometer "space tether" was deployed from the Space Shuttle in 1996, to use the shuttle's speed to generate energy. It failed spectacularly due to air trapped in the cable, creating a plasma discharge which melted the cable.

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

Co-author: Dr. Mauricio Peredo

Spanish translation by J. Méndez


Last updated 26 May 2001