Polaris vs Pole Star

Polaris

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

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

Pole Star

name
  • The star nearest to Earth's axis when extended above the North Pole: currently Polaris, formerly Thuban. 

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