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#15.   Energy

  (Files in red–history)


12. Rad. Belts

    12H. Argus 1958

12a. Inner Belt

12b. Outer Belt

13. Fast Particles

14. Synch. Orbit

15. Energy

16. The Sun

  16H. Schwabe, 1843

  16a. Schwabe paper

  16b. Carrington, 1859

17. The Corona

    Energy can be loosely defined as anything able to turn a machine.

        Electricity moves the wheels of both watches and railroad engines, heat turns the steam turbines in power stations, the chemical energy of gasoline runs a car--all these are forms of energy. Light is energy, too--a solar cell converts it to electricity, and green plants convert it to chemical energy.

        A grandfather clock is powered by weights descending from a higher level--that is "potential energy" (Thomas Jefferson at his home in Monticello had a 7-day clock run by hanging cannonballs). Speed of motion is "kinetic energy", like the energy of a turning flywheel or of the wind hitting a windmill, both of which can move machinery. And it takes energy to set up a magnetic field--even when the source is an electric current which meets no resistance, like the Earth's ring current.

    The Flow of Energy to the Magnetosphere

        Energy in physics is like money in society--a universal currency in which any physical process in nature must be paid for. A fundamental law of physics asserts that it is never lost or gained, only changed from one form to another. Both the fast-moving ions of the outer radiation belt and the fast electrons which produce the aurora contain appreciable kinetic energy, which must be supplied from somewhere.

    The ultimate source is the Sun. Nuclear processes in its core convert hydrogen to helium and produce heat, which flows to the Sun's surface. Most of the heat of the surface layers is then radiated away as sunlight, which sustains life on Earth, but a small part ends up heating the outermost layer of the Sun, the corona, to a million-degree temperature. As the hot gas of the corona--a plasma, really--expands upwards, its heat is converted to the kinetic energy of a fast flow, streaming outwards: the solar wind. Four or five days after leaving the Sun, solar wind plasma hits the magnetosphere, an obstacle in its path. As it flows around that obstacle, some kinetic energy is withdrawn, ultimately powering the aurora and a variety of other processes.

    The above is the basic chain by which energy reaches the magnetosphere. Many links however remain obscure: Why is the corona so hot? How is solar wind energy transmitted to the magnetosphere? How are particles injected into the inner magnetosphere during magnetic storms? There exist clues, theories and observations, but only partial understanding.

Further Exploring

    The sister-site of "Exploration," "From Stargazers to Starships," contains a detailed discussion of physics and of solar physics. It contains much more about energy and more about energy generation by the Sun--but be warned, what you will find is a rather extensive and detailed exposition!

Next Stop: 16. The Sun

Last updated 25 November 2001
Re-formatted 3-12-2006