Between the blue sky above us and the infinite blackness of space lies a frontier full of enigmas that scientists have only just begun to investigate. It takes viewers on an exploration to probe the earth-space boundary zone, which is home to some of nature's most puzzling and alluring phenomena: the shimmering aurora, streaking meteors, and fleeting flashes that shoot upwards from thunderclouds, known as sprites.

Originally broadcast as single episodes of a television program on the PBS series NOVA in 2013.