The biggest questions facing modern astronomers, as well as how scientists are attempting to provide answers, will be explored at the University of Colorado at Â鶹ӰԺ's Fiske Planetarium on Friday, July 18, at 8 p.m. CU-Â鶹ӰԺ 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."