asterism vs star system

asterism

noun
  • An unofficial constellation (small group of stars that forms a visible pattern). 

  • A rarely used typographical symbol (⁂, three asterisks arranged in a triangle), used to call attention to a passage or to separate subchapters in a book. 

  • A star-shaped figure exhibited by some crystals by reflected light (as in a star sapphire) or by transmitted light (as in some mica). 

star system

noun
  • A group of stars (and possibly smaller bodies such as planets or asteroids) that orbit one another. 

  • A method of creating, promoting and exploiting movie stars in cinema, emphasizing on their images rather than acting. 

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