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The guest star, apparently in Centaurus, which was observed in China in the year 185AD has usually been identified with the SNR RCW86 (alias MSH 14-63). An alternative possibility (Thorsett, Nature 356, 690, 1992) is the pulsar PSR 1509-58 whose spin-down age of 1700 years is suggestively appropriate. On the other hand, the nebula, RCW89, which coincides with that pulsar shows no significant internal proper motion and so is unlikely to be a young object (van den Bergh and Kamper, ApJ 280, L51, 1984). We have now made a proper motion study of optically brightest region of the prime candidate RCW86 using plates from the Radcliff 1.9m taken in 1963 and the CTIO 4m taken in 1977 along with CCD frames from the UTSO 0.6m obtained in 1990 and 1993. The observed arc is some 1100 arc seconds from the center of symmetry of the radio source. If the nebula is in the Sedov adiabatic phase of expansion, the expected proper motion would be 0.24 $arc sec yr^{-1}$. Our measured values are more than an order of magnitude smaller and thus contradict the hypothesis of youth for this SNR. Disappointingly, the 185AD object may indeed have been merely a comet (Chin and Huang, Nature 311, 29, 1994) unless it was indeed a supernova that produced a pulsar without producing a nebular remnant.
