Light in the night sky following an airplane and then vanishing for no reason. Cloudless night sky.First I was watching a small aircraft with headlight and flashing tail beacon then I noticed another light some distance behind it traveling roughly the same direction, however this one had no flashing light. I thought it might be another airplane and I watched it for about 20-30 second and then it vanished. The sky had no cloud cover and I can think of no reason why this light/craft would vanish suddenly. I notice the same type of event two nights ago in the same area of the sky - west of Santa Rosa and fairly close.