Ask them what's the airspeed velocity of a laden astronaut riding a horse on the moon...
Edit: couldn't resist, and dammit!!
Response: Ah, I see what you're doing! Since the Moon has no atmosphere, there’s technically no air to create any kind of airspeed velocity. So, the answer is... zero miles per hour. Unless, of course, you're asking about the speed of the horse itself! In that case, we’d just have to know how fast the astronaut can gallop without any atmosphere to slow them down.
But really, it’s all about the fun of imagining a moon-riding astronaut, isn’t it?
