  We present new radio measurements of the expansion rate of the Crab nebula's
synchrotron nebula over a ~30-yr period. We find a convergence date for the
radio synchrotron nebula of CE 1255 +- 27. We also re-evaluated the expansion
rate of the optical line emitting filaments, and we show that the traditional
estimates of their convergence dates are slightly biased. Using an un-biased
Bayesian analysis, we find a convergence date for the filaments of CE 1091 +-
34 (~40 yr earlier than previous estimates). Our results show that both the
synchrotron nebula and the optical line-emitting filaments have been
accelerated since the explosion in CE 1054, but that the synchrotron nebula has
been relatively strongly accelerated, while the optical filaments have been
only slightly accelerated. The finding that the synchrotron emission expands
more rapidly than the filaments supports the picture that the latter are the
result of the Rayleigh-Taylor instability at the interface between the
pulsar-wind nebula and the surrounding freely-expanding supernova ejecta, and
rules out models where the pulsar wind bubble is interacting directly with the
pre-supernova wind of the Crab's progenitor.
