Web Pages on Physics, Astronomy, Space and Magnetism

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    Listed below are selected topics of interest covered in the above web sites. Selectings any item from the list brings you to the actual links to the pages (often more than one page is linked) and a brief description of what they contain.

    Spanish translations generally have similar names, but with a capital M replacing capital S as first letter; French ones start with F, Italian ones with I, German (in "The Great Magnet") with D, and lesson plans (only in "Stargazers") with the letter L. Go to the home pages listed above to link to the home pages of the translations and lessons.

  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.     The Transit of Venus
  15.     Free fall due to gravity
  16.     Vectors
  17.     Energy
  18.     Newton's laws of motion
  19.     Mass, and its measurement
          in a weightless environment
  20.     Newton's 2nd law
  21.     Newton's 3rd law

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

  34.     Energy sources and ultimate
          fate of the Sun and stars
  35.     Quantum physics--how it arose and
          what it means--a qualitative overview.
  36.     Nuclear Fission, nuclear power
          and nuclear weapons.
  37.     Rockets
  38.     The story of Robert H. Goddard
  39.     Recent history of rocketry
          and spaceflight.
  40.     5 types of unmanned spacecraft.
  41.     Cannons that can reach space.
  42.     Nuclear power for spaceflight
  43.     Solar sails
  44.     Ion rockets

  45.     Lagrangian points--stable
          stations in space
  46.     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.     Electricity as a Fluid
  22.       Magnetic field lines
  23.     Electrons
  24.     Plasma
  25.     The fluorescent lamp
  26.     Positive ions
  27.     Energetic particles
  28.     The Geiger counter.
  29.     Cosmic rays

  30.     High energy particles
          in the Universe
  31.     The Sun, sunspots, their
          cycle & associated outbursts.
  32.     The Sun's Corona
  33.     The solar wind
  34.     The Heliosphere
  35.     Lagrangian points
  36.     Introduction to magnetism and
          the magnetosphere (summary)
  37.     A Teacher's introduction to and
          the magnetosphere (lecture for teachers)
  38.     Folding paper model of the
          Earth's magnetosphere
  39.     The polar aurora
  40.     Motion of Trapped Radiation
  41.     Particle Drift in Space
  42.     Discovery of the radiation belt
  43.     Interplanetary field lines.

  44.     Magnetic storms and "Space Weather"
  45.     High energy particles from the Sun
  46.     The space tether experiment
  47.     The black hole at the center of
          our galaxy.

(a) From Stargazers to Starships

  1.     The pole star
    The northern polar constellations and Alaska's state flag.

  2.     The sundial
    The motion of the Sun across the sky:
    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
    The observed motion of the Sun, summer and winter:
    The reason why:
    Covers the length of the day and the angle of the Sun.
    More about that angle in
    and about the variation of the distance from the Sun (possibly linked to ice ages) is in             stargaze/Sprecess.htm

  4.     The Moon
    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
    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
    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
    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
    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
    Describes a simple parallax method for estimating distances outdoors, and how distances to stars were first measured.

  10.     The distance of the Moon
    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.
    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
    The riddle of retrograde motion of the planets, and the way it was addressed by Ptolemy and by Copernicus.

  13.     Kepler and his laws
    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:             stargaze/Sscale.htm

    The pages below contain more about the 1st and 2nd law, and about orbits.

    Also a one-hour talk given to high school teachers (3.23.2005) on "Kepler's 3 Laws of Planetary Motion", linked at stargaze/Kep3laws.htm .

  14.     The Transit of Venus and the scale of the solar system.  
    http://www.phy6.org/stargaze/Sscale.htm notes that Kepler's laws only define relative distances in the solar system. To assign to those distances their values in kilometers, some distance needs to be actually measured. An early method relied on the transit of the planet Venus in front of the Sun's disk.
          In the 3 pages below an approximate value of the Earth-Sun distance is calculated, using the transit of Venus observed on June 8, 2004:


  15.     Free fall due to gravity
    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.

  16.     Vectors
    Displacement as a vector--and continuing from there, velocity addition and resolution into components. For more on vectors, see "Airplane Flight" (item #23) below.

  17.     Energy
    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.

  18.     Newton's laws of motion
    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.

  19.     Mass, and the way it was measured in weightless environment
    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.

  20.     Newton's 2nd law
    Illustrated by the calculation of the acceleration of a rocket, at launch and at burnout.

  21.     Newton's 3rd law
    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:

  22.     How high voltages are created in the lab and in thunderstorms:
    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.

  23.     Newton's theory of universal gravitation
    Cites the original story of Newton's apple, then shows how Newton used the motion of the Moon to confirm his guess.

  24. A     Spaceflight to Mars
    Flight to Mars: How Long? Along what Path?
          Flight to Mars: Calculations
          Flight to Mars: the Return Trip
    Spaceflight from Earth to Mars and back is calculated, using the Hohmann transfer ellipse. Kepler's 3rd law gives the duration of the trip, the energy law gives the extra velocities needed when entering and leaving the transfer orbit, and the synodic period of Mars helps obtain the delay between arrival at Mars and the next opportunity to fly back (via the Hohmann ellipse).

  25.     Airplane flight
    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.
        Optional section on aerodynamics of drag, lift and the choice of flight speed and altitude

  26.     Centrifugal and centripetal forces
    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).

  27.     Motions in rotating frames of reference
    Discusses the rotation of Earth, its effect on the magnitude and direction of observed "local gravity," the cause of the Earth's equatorial bulge and (as a an example of Newton's laws changing in a rotating frame), why "local gravity" on airliners flying east and west, at the same location, is actually different.
    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.

  28.     The greenhouse effect
          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.

  29.     Thunderstorms and weather.
          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.

  30. A     Global Climate, Global Wind Flow
          About global climate and the large scale air motions which contribute to it.

  31.     The Sun and sunspots
          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,

  32.     What is color?
          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.

  33.     What makes light an "electromagnetic wave"?
          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.

  34.     The energy sources and ultimate fate of the Sun and of stars
          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.

  35. A     Quantum physics--how it arose and what it means, a qualitative overview.:

  36.     Nuclear power stations and how they work.
          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.
        is a brief overview of nuclear weapons, recently added.

  37.     Rockets
          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.

  38.     The story of Robert H. Goddard
          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.

  39.     Recent history of rocketry and spaceflight.
          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.

  40.         Five types of unmanned spacecraft.
          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.

  41.     Designing cannons to fire into space
    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.

  42.     Nuclear power for spaceflight
    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."

  43.     Solar sails
          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.

  44.     Ion rockets
          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.

  45.     Lagrangian points--stable stations in space
          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!

  46.     How spacecraft gain speed from the gravity of planets.
    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?

  47.     The story of the Pelton turbine.
          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.

  48.     Timeline of (basic) astronomy, Newtonian mechanics and spaceflight
          A chronology of basic astronomy, mechanics and spaceflight, keyed to the "Stargazers" text. All entries are in red, with appropriate links, and they are embedded in a timeline (black print) of the history of humanity and its technology.

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

  49.     Guidance to teachers on using the "Stargazers" material
    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.

  50.         "Stargazers" and National Science Education Standards.
    Point-by-point description of the way "Stargazers" adheres to national standards.

  51.     Inventory of concepts, stories...
    Section-by-section listing of (1) Concepts covered (2) Calculations and formulas (3) Stories, extensions and examples

  52.     Problems
    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:

    (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").

  53.     A short course on the Earth's Magnetism in Earth Science Class
    The text and slides of a 1-hour invited talk presented to a meeting of the Natl. Science Teachers Association in Baltimore, 18 Nov. 2000.
          Three classroom demonstrations on magnetism, suitable for being performed on top of an opaque projector ("vu-graph"):

          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.

  54.     The early history of magnetism
    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.

  55.     William Gilbert's book "De Magnete" (1600).
    Two reviews of the book, and some additional details.

    One of Gilbert's experiments, which can be duplicated with simple equipment.
    London in 1600--the city of William Gilbert, also of Queen Elizabeth and Shakespeare

  56.     Magnetism from Gilbert to 1820
    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.

  57.     The link between electricity and magnetism, and how it was found
    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 an easy table-top duplication of his experiment.

  58.     Lodestones
    If natural stone-magnets did not exist, humanity might not have discovered the compass as early as it did--and Columbus might not have discovered America. An accident of nature, they are probably created by lightning.

  59.     Gauss and the first magnetic survey
    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.

  60.     The Sun's magnetism and the sunspot cycle.
    This is covered and described in item #28 above, and also in
    and its linked files

  61.     Fluid dynamos and the magnetism of the Earth
    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.

  62.     Modern magnetometers and their use in research.
    Until about 1950 magnetism was measured by magnetic needles suspended on fine strings. Then electronic magnetometers were developed, and one type, the fluxgate instrument, is described here. They are the obvious choice for magnetic observations 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.

  63.     Magnetic Reversals and moving continents
    When molten lava solidifies, it records the direction of the surrounding magnetic field. For recent lava flows, this is always found to point north-south--but ancient lava sometimes recorded reversed fields. That was explained by dynamo theory (#57 above), and became unexpectedly the central clue in tracing 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.

  64.     The magnetic space environment around Earth
    The Earth's magnetic influence extends into space around it, confining radiation belts, producing the polar aurora ("northern lights") and sustaining "magnetic storms," related to by events on the Sun.

  65.     Magnetism of other planets.
    The Earth is not the only magnetic planet: space probes have shown that the giant gas planets--Jupiter, Saturn, Uranus and Neptune--are all magnets more powerful than Earth. The magnetic field and radiation belt of Jupiter are particularly intense, 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 assembled before 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.

            Yet... it also has a quick introduction to magnetism, electrons and ions, plasmas and some other concepts of modern physics, as well as to the Sun and some other astronomical subjects. All these subjects may be relevant to the high school curriculum, and they include:

  66.     The link between electricity and magnetism and its discovery by Oersted
    This material is similar to #53 above and includes the same table-top experiment.

  67.     Electricity as a Fluid
      A brief introduction to the flow of electric currents, and to the concepts of electric voltage and electric field.

  68.     Magnetic field lines (or "lines of force")
    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

  69.     Electrons
    All atoms contain tiny particles charged with negative electricity. Many clues to their existence were seen before J.J. Thomson discovered them in 1897; one of those is 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:

  70.     Plasma
    Plasma is a gas hot enough for electrons to be torn off their atoms, making such a gas 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).

  71.     The fluorescent lamp: a plasma you can use.
    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.

  72.     Positive ions
    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?

  73.     Energetic particles
    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).

  74.     The Geiger counter.
    Among the earliest and most versatile radiation detectors, one version of which discovered the radiation belt of Earth.

  75.     Cosmic rays
    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. Includes new results, released in 2004, from giant gamma ray telescopes.

  76.     High energy particles in the Universe
    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. Includes information on the SWIFT satellites, launched in 2004.

  77.     The Sun, its sunspots, sunspot cycle and associated outbursts.

    The Sun--Introduction and Links, a "home page" linking to web pages in the three collections, related to phenomena on the Sun.
    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, sustaining 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:
    The discovery of explosive events near sunspots, by Richard Carrington in 1859:

  78.     The Sun's Corona
    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).

  79.     The solar wind
    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.

  80.     The Heliosphere
    The solar wind is ultimately stopped by the pressure of the interstellar gas. Voyager 1 crossed the first boundary on 16 December 2005, at about 94 AU, passing the termination shock where the solar wind abruptly slows down. The actual boundary of the "heliosphere" lies still further out.

  81.     Lagrangian points
    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:

  82.     Introduction to magnetism and the magnetosphere (summary file)
    The first of 8 files which together summarize this web site and link to more detailed web pages.

  83. A     A Teacher's Introduction to the Earth's Magnetosphere--lecture prepared for teachers:

  84.     Folding paper model of the Earth's magnetosphere
    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.

  85.     The polar aurora
    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."
    as well as a very extensive self contained discussion of the aurora and related science and history, at

    On 5 November 2001 aurora was observed in many parts of the US, following the onset of a significant magnetic storm (see #81 below). A related e-mail exchange "Aurora over Chicago" which shows links between this aurora and the magnetic storm is given at

  86.     Motion of trapped radiation
    Ions and electrons in the radiation belt are attached to magnetic field lines "like beads on a wire", though they may slowly shift from one line to its neighbor. In this process they exhibit three distinct periodicities, which govern the motion of trapped radiation belt particles. The stability of this motion is maintained by the near-perfect (but not absolute!) preservation of a certain property of the motion.

  87.     Particle Drift in Space
    How ions and electrons in space, while attached to magnetic field lines manage to slowly "drift" from one line to another.

  88.     Discovery of the radiation belt
    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.

  89.     The shape of interplanetary field lines.
    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.

  90.     Magnetic storms and "Space Weather"
    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
      On the magnetic storm of 5 November 2001, with reports by aurora watchers in Chicago and Virginia:

  91.     High energy particles emitted by the Sun
    Outbursts on the Sun--associated with sunspot activity--sometimes accelerate ions and electrons to quite high energies.

  92.     The space tether experiment (see also #57 on the "dynamo effect")
    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.

  93.     The black hole at the Center of our Galaxy
    At the center of our galaxy, helping hold it together, is a black hole about 3.7 million times more massive than the Sun. Recent evidence comes from a large star orbiting this mass, tracked by a sophisticated infra-red camera on a large telescope.

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

Last updated 12-13-2004