We have constructed a series of non-rotating quasi-hydrostatic evolutionary models for the M2 Iab supergiant Betelgeuse ( \alpha~ { } Orionis ) .
Our models are constrained by multiple observed values for the temperature , luminosity , surface composition and mass loss for this star , along with the parallax distance and high resolution imagery that determines its radius .
We have then applied our best-fit models to analyze the observed variations in surface luminosity and the size of detected surface bright spots as the result of up-flowing convective material from regions of high temperature in the surface convective zone .
We also attempt to explain the intermittently observed periodic variability in a simple radial linear adiabatic pulsation model .
Based upon the best fit to all observed data , we suggest a best progenitor mass estimate of 20 ^ { +5 } _ { -3 } M _ { \odot } and a current age from the start of the zero-age main sequence of 8.0 - 8.5 Myr based upon the observed ejected mass while on the giant branch .