The world's most powerful telescope unfurled its final mirror today as it sped away to its final destination one million miles from earth. NASA completed the final step of the Webb telescope's difficult two-week initiation process Saturday, unfolding the final 21-foot piece: its 'golden eye.' NPR science correspondent Joe Palca joins Hari Sreenivasan to explain more about the telescope, its design, and its purpose. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders