sky vs troposphere

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. 

troposphere

noun
  • The lower levels of the atmosphere extending from the surface of the Earth or another celestial body up to the tropopause. It is characterized by convective air movements and a large vertical temperature change. 

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