  We employ a technique that combines the configuration interaction method with
the singles-doubles coupled-cluster method to perform calculation of the energy
levels, transition amplitudes, lifetimes, g-factors, and magnetic dipole and
electric quadrupole hyperfine structure constants for many low-lying states of
neutral actinium. We find very good agreement with existing experimental energy
levels and make accurate predictions for missing levels. It has been noted that
some of the levels have been previously misidentified; our analysis supports
this claim. If spectroscopy is performed with actinium-225, our calculations
will lead to values for nuclear structure constants. The accuracy of this can
be constrained by comparing with actinium-227.
