The length of the magnetospheric tail

Dessler's [1964] theoretical reasonings lead him to conclude that the magnetosphere has a tail of astronomical length. If the ‘open model’ [Dungey, 1963] is assumed, however, an empirical estimate can be obtained very simply, and it is more reasonable. A line of force of the interplanetary field becomes attached to the earth in the region of local noon and 75° geomagnetic latitude. The terrestrial end of the line then moves over the pole to the night side and the line becomes detached again when the terrestrial end reaches a geomagnetic latitude of about 67°.