  The star formation rate history of the Milky Way is derived using the
chromospheric age distribution for 552 stars in the solar neighborhood. The
stars sample birthsites distributed over a very large range of distances
because of orbital diffusion, and so give an estimate of the global star
formation rate history. The derivation incorporates the metallicity dependence
of chromospheric emission at a given age, and corrections to account for
incompleteness, scale height-age correlations, and stellar evolutionary
effects. The results show that the Milky Way has undergone fluctuations in the
global star formation rate with amplitudes greater than a factor of 2-3 on
timescales less than 0.2-1 Gyr. The actual history is likely to be more bursty
than found here because of the smearing effect of age uncertainties. There is
some evidence for a slow secular increase in the star formation rate, perhaps a
record of the accumulation history of our galaxy. A smooth nearly-constant star
formation rate history is strongly ruled out, confirming the result first
discovered by Barry (1988) using a smaller sample and a different age
calibration. This result suggests that galaxies can fluctuate coherently on
large scales.
