PFP 1 a large faint Planetary Nebula in MonocerosDiscovered in 2004 by astronomers Mark J. Pierce, David J. Frew and Quentin A. Parker, PFP 1 (aka PN G222.1+03.9) is a remarkably annular planetary nebula located in Monoceros measuring 19 arc-minutes across making it one of the largest of its type. PFP 1 has an estimated radius of 1.5 parsec and has near perfect symmetry, broken only at the north west edge which is coupled with significantly increased hydrogen atom intensity. This arc of intense nebulosity was previously detected in POSS I and II red plates and those of the SERC ER survey as an elongated wisp of nebulosity. The large diameter ring is near undetectable due to its extremely low surface brightness. PFP 1 is estimated as being 1,800 light years away. This is a previously unknown, highly evolved planetary nebula of low excitation which is in the first stages of an interaction with the interstellar medium (ISM).It was discovered serendipitously from AAO/UKST Hα Survey images as part of a project to exploit the survey data and has evaded detection by previous surveys due to its very low surface brightness.It is a remarkable hollow-sphere planetary nebula, some 19 ′across, making it one of the largest examples of its type. We estimate a radius of 1.5 pc and a distance of 550 pc as derived from a new Hα surface brightness– radius relation. PFP 1 has near-perfect circular symmetry, broken only at the north-western edge which is coupled with significantly increased (Hα + [Nii]) intensity, both of which provide evidence for an interactionwith the ISM. We find a near solar composition for this object with possibly enhanced He and N abundances.A blue central star candidate has been identified from the SuperCosmos Sky Survey data.The distance, coupled with the estimated ǫ = 0.3 based on the PN geometry, gives a nebular mass of 0.6 M ⊙ which is consistent with other highly evolved PNe. A good candidate CS has been identified from UKST B J and R plates. Follow up spectroscopy is planned to confirm whether this is the true central star.The lack of adjacent CO and IRAS dust emission explains why PFP 1 has been able to expand unencumbered to its present size of ∼3.0 pc. We find two possible causes for the interaction evident on the north-western rim — the motion of the PN with respect to its surroundings as per Borkowski et al. (1990) or an encounter with a region of enhanced density as it expands. We are unable to state conclusively which is responsible based on the available data. An accurate proper motion determination of the CS candidate would be useful in establishing which of these scenarios is most likely. Analysis of moderate resolution spectra has shown that this is a PN of low excitation, which is consistent with other large-diameter senile examples.Although the spectra have low signal-to-noise, the chemical composition of this PN is probably close to solar, and while it exhibits a high [Nii]/Hα ratio it is doubtful whether it is a bona fide Type I PN as defined by Kingsburgh & Barlow (1994).The same technique which led to the discovery of PFP 1 has furnished us with ∼30 other candidate PNe of size >4 ′ . A follow up program is underway to obtain spectra and narrowband imaging of this sample.