sky vs stratosphere

sky

noun
  • The atmosphere above a given point, especially as visible from the surface of the Earth as the place where the sun, moon, stars, and clouds are seen. 

  • With a descriptive word: the part of the sky which can be seen from a specific place or at a specific time; its climate, condition, etc. 

  • The set of all lightlike lines (or directions) passing through a given point in space-time. 

verb
  • To move quickly, as if by flying; to fly; also, to escape, to flee (especially by airplane). 

  • To hit, kick, or throw (a ball) extremely high. 

  • To clear (a high jump bar, hurdle, etc.) by a large margin. 

  • To hit, kick, or throw a ball extremely high. 

  • To raise an oar too high above the water. 

  • To drink (a beverage) from a container without one's lips touching the container. 

stratosphere

noun
  • The region of the uppermost atmosphere where temperature increases along with the altitude due to the absorption of solar ultraviolet radiation by ozone. The stratosphere extends from the tropopause (10–15 kilometers) to approximately 50 kilometers, where it is succeeded by the mesosphere. 

How often have the words sky and stratosphere occurred in a corpus of books? (source: Google Ngram Viewer )