In the solar wind, the area of demarcation between sectors. which are large-scale features distinguished by the predominant direction of the interplanetary magnetic field, toward the Sun (a negative s
ector), or away from the Sun (a positive sector). The sector boundary separating fields of opposite polarity is normally narrow, passing the Earth within minutes to hours as opposed to the week or so needed for passage of a typical sector. The solar wind velocities in the boundary region are typically among the lowest observed.
A sector boundary crossing is a transit by aspacecraft across the heliospheric current sheet separating the dominantlyoutward (away-from-the-sun) interplanetary magnetic field of one hemisphereof the
heliosphere from the dominantly inward (toward-the-sun) polarity ofthe other hemisphere. Such crossings have multi-day intervals of oppositeIMF dominant polarities on either side.
The angle subtended at a star by a baseline that is the distance the Sun moves in a given interval of time with respect to the local standard of rest (4.09 AU per year).