The biggest questions facing modern astronomers, as well as how scientists are attempting to provide answers, will be explored at the ÀÖ²¥´«Ã½ at Boulder's Fiske Planetarium on Friday, July 18, at 8 p.m. CU-Boulder astronomer and author Jeffrey Bennett will attempt to put a few of the great mysteries of space into context for people attending his presentation, "On the Cosmic Horizon: Ten Great Mysteries for Third Millennium Astronomy."