We report new mid-infrared and radio images of the M supergiant alpha Orionis. The radio images, taken with MERLIN and the Very Large Array, resolve the chromosphere of the star at a wavelength of 6cm, showing that the radio-emitting region has between two and three times the diameter of the optical photosphere. The infrared images, taken at the UK Infrared Telescope (UKIRT) using the Berkeley Infrared Camera, show that the dust shell is resolved. Images taken one year apart show great changes in morphology, which suggests that the dust shell is being asymmetrically illuminated by a stellar radiation field that is strongly affected by the presence and evolution of spots on the stellar surface. We present a new model of the circumstellar environment of the star, which fits the infrared and radio images and the spectral energy distribution (SED), and is consistent with recently reported Hubble Space Telescope observations. The chromospheric structure is determined quantitatively and the inner dust shell structure qualitatively with this model. We find that the inner radius of the dust shell is approximately 0.5arcsec, which disagrees with a number of interferometric measurements that have resulted in an inner radius close to 1.0arcsec. We are unable to explain this difference.