The next few chapters investigate recent discoveries about the solar system following the path of Sagan’s career. First, Sagan narrates the first viewings of Earth’s atmosphere from space: the 1957 flight by David Simons, the first person to reach 30 kilometers above Earth, and the 1961 Vostok mission in which Yuri Gagarin became the first human to reach orbit. Both men describe a gradual purple change from blue sky to black space at the edges of the atmosphere.

Sagan introduces the science of light to explain why Earth’s sky appears blue. Light from the Sun breaks down into multiple colors of varying wavelengths, with the blue wavelengths being the shortest and red the longest. The shorter light wavelengths bounce around in the atmosphere, which is why the sky seems blue, while sunsets look red because the dense air by the horizon has scattered most of the shorter wavelengths, leaving only the longer wavelength colors. Here Sagan makes a point that sunsets are no less beautiful when we know the science behind that beauty.

Sagan then explains why other worlds have different skies. Some worlds are too small, without enough gravity to retain atmospheres; their skies are the black of space.