Relativistically expanding spherical emitters

Abstract

We demonstrate several relativistic effects associated with expanding spherical sources of light. We show that if the surface lights up for say a month, it may be seen for a few seconds only if it expands sufficiently fast. Also it is demonstrated how the observed properties of the light source are modified by aberration and the Doppler effect. The apparent luminosity as a function of time is calculated and shown graphically. Modifications due to the motion of the light source away from the observer are calculated.