Determination of the direction of the interstellar medium motion relative to the Sun by measurements of interstellar pickup ion helium

One of the main methods to measure the direction of the interstellar medium flow relative to the Sun is to measure parameters of interstellar pickup helium atoms at the Earth orbit or at its nearest neighbourhood. Pickup ions are formed in the interplanetary medium through photoionization of interstellar helium atoms. Charge exchange in the region of interaction of the solar wind with interstellar medium no effect on distribution of the atoms. Thus, the helium ions in the inner regions of the heliosphere carry information about the interstellar medium, and measurements of charged particles on spacecraft are much simpler than neutral atoms directly. Here, however, when one try to determine the direction of the interstellar flow exactly, some problems of "transport" nature can occur. These problems can sometimes result in unexpected "discoveries". All these aspects are discussed in the paper. (paper)