 Radial velocity is measured by the doppler shift of the star 's spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc seconds ( mas ) per year . With knowledge of the star 's parallax and its distance , the proper motion velocity can be calculated . Together with the radial velocity , the total velocity can be calculated . Stars with high rates of proper motion are likely to be relatively close to the Sun , making them good candidates for parallax measurements . 
 Radial velocity is measured by the doppler shift of the star <a href='null_genetive' title='1'><mark>'s</mark></a>spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc seconds ( mas ) per year . With knowledge of the star <a href='null_genetive' title='2'><mark>'s</mark></a>parallax and its distance , the proper motion velocity can be calculated . Together with the radial velocity , the total velocity can be calculated . Stars with high rates of proper motion <a href='drop_aux' title='3'><mark>are</mark></a>likely to be relatively close to the Sun , making them good candidates for parallax measurements . 
Radial velocity is measured by da doppler shift of the star  spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc secs ( mas ) per year . With knowledge of tdastar  parallax and its distance , thdaroper motion velocity can be calculated . Together wid the radial velocity , thedatal velocity can be calculated . Stars with high rates of proper motion likely to b relatively close to the da , making em gud candidates fir parallax measurements .