What's the chance that the source of the light is not from an explosion, but from the accumulation of photons? The concept would be Dopplewr in nature and similar to sound when the source is moving toward the observer. The rays of photons are emitted forward with a shorter wave lenght by C - speed of Holmes comet. The higher intensity would occur when the comet is aimed most directly toward the observer. Additionally, those rays sent out nearly forward would arrive in a group as their forward motion would exceed their sideways motion. They would thus produce the halo seen for Holmes.