The distance of BL Lac

An upper limit on the distance of BL Lac is derived assuming that (a) the optical continuum is synchrotron radiation produced by relativistic electrons; (b) the magnetic field has the value appropriate for equipartition of energy; (c) the optical object lies within the radio component. The upper limit obtained depends on the mechanism of electron production. Limits are also obtained on the magnetic field and mass of BL Lac, and the possibility that it may be a galaxy in the process of formation is explored.