Rational debate over the existence and relevance of extraterrestrial beings has imbued Christian theology since the middle ages; and it continued right down into the modern era of astronomy. "The extent of the debate is suggested by the fact that, by 1916, more than 140 books (not counting works of science fiction) and thousands of articles addressing this issue had already appeared....Not least surprising is the fact that authors found ways to marshal extraterrestrials in support of, or in opposition to, Christianity, deism, atheism, and dozens of other creeds and philosophies" (Crowe, 2000, p.343).