text:  Capitol Fourth, the annual concert and fireworks display is getting underway at this hour and will be broadcast live from Washington, D.C. Smokey Robinson, Fantasia, and Darren Criss among the performers. NPR's Elizabeth Blair has more. In addition to commemorating the nation's independence, two musical anniversaries will be celebrated. Pianist Chloe Flower will perform Gershwin's Rhapsody in Blue, which is marking its centennial.