Half-arc angle

{
  "id": "MLC-T-MET-006150",
  "term": "Half-arc angle",
  "field": "Meteorology and atmospheric science",
  "definition": "The elevation angle of the point in the sky that an observer judges to be halfway between the horizon and the zenith. The sky vault looks flattened rather than hemispherical, so this apparent midpoint lies well below 45 degrees, typically near 20 to 30 degrees above the horizon. It is measured with an angle meter and varies with sky brightness and cloud conditions, which makes it an index of the perceived shape of the sky.",
  "url": "https://mlchart.com/terminology/meteorology/half-arc-angle/"
}