This drawing shows the difference between a dipole and a magnetosphere.
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Image from the AGU Educator's Slide set. Image copyright 1997 by the American Geophysical Union. Further electronic distribution is not allowed.
A Planetary Magnetosphere
A planetary magnetosphere is different from an ordinary dipole. The force of the solar wind, coming from the sun stretches the dipole and creates a nose region in the front of the magnetosphere (facing the sun), and a tail region in the back called a magnetotail.
If it weren't for the solar wind, the field lines of the planetary magnetic field would extend into infinity. But because the solar wind and IMF press upon a planet's magnetic field, and enclose it, the magnetic field is contained within a "cavity" called the magnetosphere. This magnetosphere naturally has a boundary and that boundary is called the magnetopause. The magnetopause can be considered to be the end of a planet's region of influence.
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