critical mass vs noon

critical mass

noun
  • The tipping point. 

  • The amount of fissile material needed to support a self-sustaining nuclear chain reaction. 

noon

noun
  • The highest point; culmination. 

  • The letter ن in the Arabic script. 

  • The time of day when the sun is in its zenith; twelve o'clock in the day, midday. 

verb
  • To relax or sleep around midday 

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