lodestar vs pole star

lodestar

noun
  • A star used as a navigation reference, particularly a pole star such as Polaris. 

  • A guiding tenet or principle. 

  • A calculated amount to award as attorney's fees derived by multiplying the reasonable number of hours spent working on a case by the reasonable hourly billing rate. 

pole star

noun
  • The star visible to the naked eye which was in the past, is now, or will be in the future nearest a celestial pole of a planet. 

  • A person, principle, or thing which acts as a guide; a guiding light; also, something which attracts much attention; a centre of attention. 

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