  To investigate the nature of starbursts' dust, we constructed a model of the
stars and dust in starburst galaxies and applied it to 30 observed starburst
spectral energy distributions (SEDs). The starburst model was constructed by
combining two stellar evolutionary synthesis models with a model describing the
radiative transfer of stellar photons through dust. The stellar evolutionary
synthesis models were used to compute the dust-free SEDs for stellar
populations with ages between 1x10^6 and 15x10^9 years. Using a Monte Carlo
radiative transfer model, the effects of dust were computed for average Milky
Way (MW) and Small Magellanic Cloud (SMC) dust, two different star/dust
geometries, and locally homogeneous or clumpy dust. Using color-color plots,
the starburst model was used to interpret the behavior of 30 starbursts with
aperture-matched UV and optical SEDs (and IR for 19 of the 30) from previous
studies. From the color-color plots, it was evident that the dust in starbursts
has an extinction curve lacking a 2175 A bump, like the SMC curve, and a steep
far-UV rise, intermediate between the MW and SMC curves. The star/dust geometry
which is able to explain the distribution of the 30 starbursts in various
color-color plots has an inner dust-free sphere of stars surrounded by an outer
star-free shell of clumpy dust. When combined with other work from the
literature on the Orion region and the 30 Dor region of the Large Magellanic
Cloud, this work implies a trend in dust properties with star formation
intensity.
