Pole-star recorder

{
  "id": "MLC-T-MET-008049",
  "term": "Pole-star recorder",
  "field": "Meteorology and atmospheric science",
  "definition": "An instrument for estimating nighttime cloud cover by taking a long-exposure photograph of the sky centered on the celestial pole. In the Northern Hemisphere, the camera is aimed at Polaris; stars leave circular trails on the film or sensor, while clouds obscure these trails or appear as a diffuse glow. The fraction of the circular star trails that are visible provides a quantitative measure of cloudiness throughout the night.",
  "url": "https://mlchart.com/terminology/meteorology/pole-star-recorder/"
}