Kapteyn used observations of the smaller shift in the position of stars that are farther away to estimate their distances. This is essentially a consequence of the angular size versus distance relationship discussed in Unit $10,$ as illustrated by the following: (a) If stars move at a typical speed of $20 \mathrm{km} / \mathrm{sec}$, how far will they move in 10 years? (b) If a star is 10 pc distant, what will its angular shift be over these 10 years? (c) If a star is 100 pc distant, what will its angular shift be?