|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Based on unpublished data taken with the PN.Spectrograph.