halcyon days vs utopia

halcyon days

noun
  • A period of calm, usually in the past and often nostalgic. 

  • Period of calm during the winter, when storms do not occur. 

utopia

noun
  • A world in which everything and everyone works in perfect harmony. 

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