How will astrology apply to peoplewho are not born on Earth?

Last year, a friend of mine asked me how (or if, really) Earth-based astrological systems will be used for people born off-planet. I'd been compiling information about some people's charts on my flight to SF, where he lives, and I'd been talking about the importance-of-the-Moon-this and the influence-of-the-ascendant-that for awhile before he put forth his question.

While it might be fair to say he's not really sold on astrology in general, he was quite sincerely interested in knowing how it could apply when (and it is just a question of when) humans are born in some extraterrestrial colony. From an information systems standpoint, he was very interested to know whether this system would still be applicable.

I thought about it and said, "Yeah, the variables would have to change." What archetype and associations would be given to Earth if one was born on the Moon? Or, if one was born on Mars, then how would its two moons relate to someone's birth? And so on and on.

My friend said that when he'd put this question to people he knew who were into astrology, they'd just get pissed or think that he was just putting astrology down. I think it's a very important consideration, and I wanted to know what anyone else thought. I don't know much about the heliocentric method, but perhaps the answer is connected to that system.