We present several different measurements of the velocities of structures within the circumstellar envelope of SN 1987A , including the inner , equatorial ring ( ER ) , the outer rings ( ORs ) , and the diffuse nebulosity at radii \lower 2.0 pt \hbox { $ \buildrel \scriptstyle < \over { \scriptstyle \sim } $ } 5 pc , based on CTIO 4m and HST data .
A comparison of STIS and WFPC2 [ N II ] \lambda 6583 loci for the rings show that the ER is expanding in radius at ( 10.5 \pm 0.3 ) km s ^ { -1 } ( with the northern OR expanding along the line of sight at \sim 26 km s ^ { -1 } , and for the southern OR , \sim 23 km s ^ { -1 } ) .
The best fit to CTIO 4m/echelle spectra of the [ N II ] \lambda 6583 line show the ORs expanding at \sim 23 km s ^ { -1 } along the line of sight .
Accounting for inclination , the best fit to all data for the expansion in radius of both ORs is 26 km s ^ { -1 } .
The ratio of the ER to the OR velocity is nearly equal to the ratio of the ER to the OR radius , so the rings are roughly homologous , all having been created \sim 20,000 yr before the SN explosion .
This makes the previously reported , large compositional differences between the ER and ORs difficult to understand .
Additionally , a grid of longslit 4m/echelle spectra centered on the SN shows two velocity components over a region roughly coextensive with the outer circumstellar envelope extending \sim 5 pc ( 20 arcsec ) from the SN .
One component is blueshifted \sim 10 km s ^ { -1 } relative to the systemic velocity of the SN , while the other is redshifted by a similar amount .
These features may represent a bipolar flow expanding from the SN , in which the ORs are propelled 10-15 km s ^ { -1 } faster than that of the surrounding envelope into which they propagate .
The kinetic timescale for the entire nebula is \buildrel \scriptstyle > \over { \scriptstyle \sim } 350,000 yr ( and probably more since material may be accumulating in an outer contact discontinuity ) .
The kinematics of these different structures constrain possible models for the evolution of the progenitor and its formation of a mass loss nebula .