In my case (over 20 years in the U-2), I never paid much attention to looking up. Most of the flying was in the daytime, and looking up for much of a 10 hour flight is boring. Additionally, in a pressure suit, the helmet hurts the neck. I did see a few, but they were just moving lights. Now comets, that was different. Because most (95%) of the obscuring atmosphere is below you, that point of light with a very small and indistinct blur for a tail that you see from the ground is a very bright center with an enormously long and distinct tail. The most impressive was Kahotek (sp?) back in the mid-70s. That one was incredible...it covered half the sky!!