hour vs sidereal day

hour

noun
  • A time period of sixty minutes; one twenty-fourth of a day. 

  • A season, moment, or time. 

  • The time. 

  • Used after a two-digit hour and a two-digit minute to indicate time. 

  • The set times of prayer, the canonical hours, the offices or services prescribed for these, or a book containing them. 

  • A distance that can be traveled in one hour. 

sidereal day

noun
  • One day of sidereal time; the time in which Earth rotates once around its axis, relative to the point of the vernal equinox (about 23 hours, 56 minutes, 4 seconds). 

  • The rotational period of Earth; the time in which Earth rotates around its axis 360 degrees. 

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