Optical mass

{
  "id": "MLC-T-MET-007709",
  "term": "Optical mass",
  "field": "Meteorology and atmospheric science",
  "definition": "A measure of the path length of sunlight through the Earth's atmosphere, relative to the path length when the sun is directly overhead (at the zenith). It quantifies the amount of atmosphere that solar radiation must traverse, affecting the intensity and spectral distribution of sunlight reaching the surface. At sea level, the optical mass is approximately 1.0 at zenith and increases as the sun approaches the horizon.",
  "url": "https://mlchart.com/terminology/meteorology/optical-mass/"
}