THE luminosity equation for the trail of a meteor is: where I is the luminous intensity at any point of the trail, is the rate of ablation of the meteoroid at that point, ν is the velocity of the meteoroid, and τ is the luminous efficiency factor which determines what fraction of the kinetic energy of the ablated atoms is converted into visible light radiation. It is generally assumed that for bright photographic meteors τ = τ0ν, where τ0 is a constant1,2. The luminosity equation therefore becomes : This means that the maximum luminosity of the trail will correspond to the level of maximum rate of ablation of the meteoroid.