Have you ever thought that when we breathe a little bit of heaven enters each of us? But what exactly is the sky? Is it possible to be struck by lightning out of the blue? What exactly is a rainbow made of? We discover all this with a journey into the 100 kilometers of air above our heads; this is by definition the sky. In the episode we try to explain what a cloud is and why the sky is blue during the day and then suddenly becomes transparent at night and allows us to see the stars that cannot be seen during the day. From the top of Etna to the sea depths of the Egadi islands: Alberto Angela among the treasures of Sicily. A journey around the island between myth and history, from Homeric legends to the various dominations of the Greeks, Romans and Arabs who left splendid archaeological traces such as the Valley of the Temples of Agrigento, the many Greek theaters such as that of the magnificent site of Segesta, up to the mosaics of Piazza Armerina.