A study of data from the Apollo lunar surface suprathermal ion detector experiment (Side) package shows that plasma flow and energy parameters in the dusk magnetosheath are much better correlated with geomagnetic activity than those in the dawn magnetosheath. This result is in agreement with a dawn-dusk asymmetry in the magnetosheath magnetic field and in the bow shock confuration. The different orientations between the mean interplanetary magnetic field direction and the shock normal for the magnetosheaths suggest an explanation of the difference in the plasma parameters on the two sides.