The authors note that humans have been fascinated with space for as long as they have been recording their history, art, and literature. Ancient epics like The Epic of Gilgamesh employ constellations as characters, and the stars have been consistently important in world religions. The invention of the telescope in the 17th century allowed humans to see, for the first time, that the bright dots in the sky were different kinds of celestial bodies. However, to explore those bodies, one first had to understand Earth’s atmosphere.

The Earth’s atmosphere consists of five different layers—the troposphere is the lowest, followed sequentially by the stratosphere, mesosphere, thermosphere, and exosphere. The authors note that the atmosphere becomes colder the higher one travels in the troposphere and stratosphere; getting closer to the sun, in this case, does not ensure warmer temperatures. This is the result of the greenhouse effect: Earth’s atmosphere allows for the penetration of the sun’s light, which becomes heated when trapped within the troposphere. As the authors note, “A July day feels hot not because the sun heated the air from above, but because the ground heated the air from below” (22-23).