So here you have two definitions of a blue moon but the one for a calendar blue moon does not describe the true meaning of a blue moon. Here's why:
Sun in Sagittarius. With the transition of the Sun into the next sign of Sagittarius we will move into a more extroverted and expanding flow of energy with many ideas and inspirations.
These icy moon-worlds are the next important step in the scientific quest for the Holy Grail of life beyond our own planet. It is a strange era in human history. Astronomers have collected large amounts of data revealing bewitching clues that habitable ocean moon-worlds may be out there, within the family of our very own Star. Humanity is poised at the beginning of a new era. Sophisticated new technology might very soon answer the profound, and very ancient question, "Are we alone?"