We only observe the small portion of the magnetic field that extends to the surface and beyond,where its basic structure is a dipole that is,a simple north south field like that of a simple bar magnet.

• 我们仅仅观察到扩展到地表和地表以外的磁场的一小部分，在这里它的基本结构是一个偶极子，就像一个简单的棒磁铁一样是一个简单的南北极磁场。