The Orrery is perhaps the least useful of all the Oblivion mods currently available. For starters, the room in question (an orrery is a planetarium of sorts) is located in the Arch Mage's tower at the Arcane University, so unless you plan on completing the Mage's Guild recommendation questions, you're not even going to have access to it. Even those who already have access to the University will probably find the Orrery to be a bit disappointing.

The quest starts when you receive a journal update, telling you that the various Dwarven artifacts needed to repair the Orrery (that door in the lobby of the Mage's Tower that you can't open) have been stolen by bandits. The location of the first bandit camp is obligingly marked on your map, so off you go. The first bandit conveniently has a letter on his person that details the locations of the rest of the bandit crew, each one possessing a different dwarven artifact. The fights shouldn't be too difficult for high-level characters, but players with lower-level characters should be warned that some of the camps have multiple bandits, and fast travelling smack into the middle of camp just might not be the best approach.

Once you've collected all the dwarven bits and pieces, you can hand them over to Bothiel at the Mage's Tower, who will then repair the Orrery. Once fixed, the Orrery is a pretty nifty sight, but doesn't actually do much of anything. You can get a buff based on whatever phase of the moon is occurring at the moment, but it's the once-a-day kind. So, all in all, the Orrery mod isn't bad, isn't good, it's just kind of there.