Relative angular momentum

In celestial mechanics, the relative angular momentum ( H 2 / 1 {displaystyle mathbf {H_{{2}/{1}}} ,!} ) of an orbiting body ( m 2 {displaystyle m_{2},!} ) relative to a central body ( m 1 {displaystyle m_{1},!} ) is the moment of ( m 2 {displaystyle m_{2},!} )'s relative linear momentum: In celestial mechanics, the relative angular momentum ( H 2 / 1 {displaystyle mathbf {H_{{2}/{1}}} ,!} ) of an orbiting body ( m 2 {displaystyle m_{2},!} ) relative to a central body ( m 1 {displaystyle m_{1},!} ) is the moment of ( m 2 {displaystyle m_{2},!} )'s relative linear momentum: