dawn vs solar day

dawn

noun
  • The time when the sun rises. 

  • The rising of the sun. 

  • The earliest phase of something. 

  • The morning twilight period immediately before sunrise. 

verb
  • To begin to give promise; to begin to appear or to expand. 

  • To begin to brighten with daylight. 

  • To start to appear or be realized. 

solar day

noun
  • one day of solar time, the time between successive noons; the time in which a planet such as Earth apparently rotates once around its axis, relative to the sun (on Earth about 24 hours as an average - the length of solar day is not constant throughout the year) 

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