Planetary Nebulae (PNe) are excellent probes of a distant galaxy's
rotational dynamics. Through their strong [O III] emission line at
5007Å rest wavelength they can be easily detected and their radial
velocity determined, allowing the stellar kinematics in the (otherwise
inaccessible) outer regions of elliptical galaxies to be studied.
In addition, it is now widely accepted that their
luminosity in the [O III] line (for an ensemble of PNe this is called the
PNLF - Planetary Nebula Luminosity Function) has a fairly sharp
bright-end cutoff, which means that they can be used as `standard
candles' in determining distances.
The PNS project aims to build a dedicated Planetary Nebula Spectrograph
in order to push this technique to its limit. We have proven that two
counter-dispersed images contain the information needed to obtain
distances and dynamics in a single observation - to our
knowledge the only way of doing so!