The WFPC2 camera aboard the Hubble Space Telescope was used to obtain images of the planetary nebula BD+30 ^ { \circ } 3639 at two epochs separated by 5.663 years .
The expansion of the nebula in the H \alpha and [ N ii ] bands has been measured using several methods .
Detailed expansion maps for both emission lines were constructed from nearly 200 almost independent features .
There is good agreement between the ( independent ) H \alpha and [ N II ] proper motions .
There are clear deviations from uniform radial expansion , with higher expansion rates in regions where the shell is faintest , such as the south-west quadrant .

The Space Telescope Imaging Spectrograph ( STIS ) was used to obtain echelle spectra in the C II ] \lambda 2326 multiplet and the [ O II ] \lambda 2470 doublet , providing well-resolved expansion velocities at two position angles .
From the C II ] lines , we find that the central velocity split is \pm 36.3 km s ^ { -1 } at a position angle of 99 ^ { \circ } , and \pm 33.5 km s ^ { -1 } at p.a .
25 ^ { \circ } .
The fainter [ O II ] doublet does not appear to differ from the C II ] multiplet .

To determine the distance of BD+30 ^ { \circ } 3639 by comparison of the angular expansion and the spectroscopically determined radial expansion , we must address the problem of the three dimensional shape of the nebula .
We measured the angular expansion along the position of the 99 ^ { \circ } echelle slit , finding displacements of 4.25 mas yr ^ { -1 } at the shell edge ( 2 \farcs 47 from the center ) .
If the nebula were spherical , this would imply a distance of 1.80 kpc .
But there is evidence that the nebula is elongated along the line of sight , which suggests that the actual distance is less .
Radio continuum images from 5 and 15 GHz VLA observations provide information on the extent of the radial elongation .
We fit the radio brightness variation and the echelle data by approximating the nebula as an ellipsoid , also making use of the ground-based echelle spectra reported by Bryce & Mellema ( 1999 , MNRAS , 309 , 731 ) .
Our model has an axial ratio of 1.56 , is inclined to the line of sight by 9 \fdg 7 , and exhibits an expansion in the plane of the sky which is 2/3 that in the radial direction , leading to a distance of 1.2 kpc .
Not all the kinematic data fits this simple model , so the distance must still be regarded as uncertain .

Based on the recent model atmosphere of Crowther et al .
( 5 ) , a distance of 1.2 kpc implies a stellar luminosity of 4250 L _ { \odot } .
The kinematic age of the nebula , \theta / \dot { \theta } , varies somewhat from region to region .
A good average value is 800 years , while the expansion along the position of the 99 ^ { \circ } echelle slit gives about 600 years .