Polaris vs polar star

Polaris

name
  • A type of U.S. ballistic missile, capable of carrying a nuclear warhead and designed to be launched from a submarine. 

  • The pole star, a trinary star in the constellation Ursa Minor that currently lies close to the north celestial pole; Alpha (α) Ursae Minoris 

polar star

noun
  • Synonym of pole star 

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