Earth's magnetic field (also known as the geomagnetic field) is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun. Its magnitude at the Earth's surface ranges from 25 to 65 microteslas (0.25 to 0.65 gauss). It is approximately the field of a magnetic dipole tilted at an angle of 11 degrees with respect to the rotational axis—as if there were a bar magnet placed at that angle at the center of the Earth. However, unlike the field of a bar magnet, Earth's field changes over time because it is generated by the motion of molten iron alloys in the Earth's outer core (the geodynamo).
The Magnetic North Pole wanders, but slowly enough that a simple compass remains useful for navigation. At random intervals (averaging several hundred thousand years) the Earth's field reverses (the north and south geomagnetic poles change places with each other). These reversals leave a record in rocks that allow paleomagnetists to calculate past motions of continents and ocean floors as a result of plate tectonics.
The region above the ionosphere, and extending several tens of thousands of kilometers into space, is called the magnetosphere. This region protects the Earth from cosmic rays that would strip away the upper atmosphere, including the ozone layer that protects the earth from harmful ultraviolet radiation.
Famous quotes containing the words field, earth and/or magnetic:
“The woman ... turned her melancholy tone into a scolding one. She was not very young, and the wrinkles in her face were filled with drops of water which had fallen from her eyes, which, with the yellowness of her complexion, made a figure not unlike a field in the decline of the year, when the harvest is gathered in and a smart shower of rain has filled the furrows with water. Her voice was so shrill that they all jumped into the coach as fast as they could and drove from the door.”
—Sarah Fielding (17101768)
“One generation passeth away, and another generation cometh: but the earth abideth for ever. The sun also ariseth, and the sun goeth down, and hasteth to the place where he arose.”
—Bible: Hebrew Ecclesiastes 1:4,5.
Ernest Hemingways book title The Sun Also Rises (1926)
“We are in great haste to construct a magnetic telegraph from Maine to Texas; but Maine and Texas, it may be, have nothing important to communicate.”
—Henry David Thoreau (18171862)