Blue moon

{
  "id": "MLC-T-MET-003960",
  "term": "Blue moon",
  "field": "Meteorology and atmospheric science",
  "definition": "The second full moon occurring within a single calendar month, or the third full moon in an astronomical season that has four full moons. This phenomenon is purely calendrical and does not refer to the moon's actual color, though atmospheric conditions can sometimes make the moon appear bluish. It occurs approximately once every two to three years.",
  "url": "https://mlchart.com/terminology/meteorology/blue-moon/"
}