The star formation rate history of the Milky Way is derived using the chrom
ospheric age distribution for 552 stars in the solar neighborhood. The star
s' sample birth sites are distributed over a very large range of distances
because of orbital diffusion and so give an estimate of the global star for
mation rate history. The derivation incorporates the metallicity dependence
of chromospheric emission at a given age and corrections to account for in
completeness, scale height-age correlations, and stellar evolutionary effec
ts. We find 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 inc
rease in the star formation rate, perhaps a record of the accumulation hist
ory of our Galaxy. A smooth, nearly constant star formation rate history is
strongly ruled out, confirming the result first discovered by Barry using
a smaller sample and a different age calibration. This result suggests that
galaxies can fluctuate coherently on large scales.