asterism vs zodiac

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). 

zodiac

noun
  • Any of various astrological systems considered similar to the above. 

  • The twelve equal divisions of the zodiacal region into signs or houses, each named for a prominent constellation in the region. 

  • A circle decorated with the signs of the zodiac. 

  • The ecliptic: the belt-like region of the celestial sphere corresponding to the apparent path of the sun over the course of a year. 

  • The belt-like region of the celestial sphere approximately eight degrees north and south of the ecliptic which include the apparent path of the sun, moon, and visible planets. 

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