The detection of Planetary Nebulae in external galaxies
by means of narrow-band imaging in the green [O III] 5007A
line inspires this image of the elliptical galaxy NGC 3379
on which the position of some 200 PNe have been superimposed.
The dots represent genuine detections.
As the movie progresses the green dots (detected PN) change to
blue or red, representing the determination of the radial
velocity: blue for approaching and red for receding with
respect to the galaxy's systemic velocity. The size of each
dot is proportional to the velocity.
Based on unpublished data taken with the PN.Spectrograph.