I don't have access to the Journal of Discourses, so I can't look and see what was said. It might make better sense in the original than in the reports rendered by scoffers. In any case, remember, each prophet is also a student, with God as his teacher. Students make mistakes, and learn from them. And the teacher lets them make mistakes because that is a major learning tool. Since no such teaching was perpetuated I'm willing to consider it an isolated error, dropped when it was discovered to be such. Only the words God gives the prophet are sure to be error free.

Oh, didn't you know? They're hollow, and the people are on the inside.

Have you got any other sources to back up the assertion that Brigham Young taught this? http://www.answerbag.com/q_view/1277381

The Man in the Moon is common knowledge ;)

First of all, as Glenn rightly pointed out, you’re citing an unofficial compilation of some guys’ shorthand conference notes—one that, I might add, often contradicts not only Church doctrine but even itself. But let’s set that aside for a moment. If we assume, just for a moment, that this transcription accurately reflects what “Brother Brigham” said, in this discourse, we should at least look at the exact words recorded:    “We are called ignorant; so we are: but what of it? Are not all ignorant? I rather     think so. Who can tell us of the inhabitants of this little planet that shines of an     evening, called the moon? When we view its face we may see what is termed     ‘the man in the moon,’ and what some philosophers declare are the shadows     of mountains. But these sayings are very vague, and amount to nothing; and     when you inquire about the inhabitants of that sphere you find that the most     learned are as ignorant in regard to them as the most ignorant of their fellows.     So it is with regard to the inhabitants of the sun. Do you think it is inhabited?     I rather think it is. Do you think there is any life there? No question of it; it was     not made in vain.” etc. (*Journal of Discourses* 13:271, available online at     http://scriptures.byu.edu .) So let’s break it down: 1. People call the Latter-day Saints (including myself) ignorant, and we are. 2. So are the people that are calling us that. 3. For example, they can’t tell us what the Sun or the Moon is like, let alone the inhabitants thereof. 4. Yes, I said “inhabitants.” IMHO, the Sun is an inhabited, celestial world. Frankly, there’s no question of it, in my mind. Why else would it be there? As you can see, the actual text simply shows that Brigham Young was as much a product of his times as anyone else—hardly the smoking gun your question seems to imply. Secondly, the Church doesn’t tend to involve itself with scientific evidence of much of anything. It’s a Church, not a research lab. Besides, what Brigham Young did or didn’t believe, on his own time, is really quite immaterial to anyone else’s salvation but his own, dontcha think?