epoch vs sidereal day

epoch

noun
  • A specific instant in time, chosen as the point of reference or zero value of a system that involves identifying instants of time. 

  • A geochronologic unit of hundreds of thousands to millions of years; a subdivision of a period, and subdivided into ages (or sometimes subepochs). 

  • A particular period of history, or of a person's life, especially one considered noteworthy or remarkable. 

  • A notable event which marks the beginning of such a period. 

  • One complete presentation of the training data set to an iterative machine learning algorithm. 

verb
  • To divide (data) into segments by time period. 

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 epoch and sidereal day occurred in a corpus of books? (source: Google Ngram Viewer )