Astronomical horizon

{
  "id": "MLC-T-MET-003653",
  "term": "Astronomical horizon",
  "field": "Meteorology and atmospheric science",
  "definition": "The great circle on the celestial sphere whose plane is perpendicular to the observer's zenith-nadir line, representing the boundary between the visible and invisible parts of the celestial sphere. It is a theoretical concept, distinct from the visible or sensible horizon, and is used as a reference in astronomical calculations. This horizon is defined by the observer's location and is unaffected by terrain or atmospheric refraction.",
  "url": "https://mlchart.com/terminology/meteorology/astronomical-horizon/"
}