[
  {
    "id": "usno",
    "url": "https://aa.usno.navy.mil/faq/RST_defs",
    "title": "US Naval Observatory: Rise, Set, and Twilight Definitions",
    "accessedAt": "2026-10-26",
    "role": "Authoritative -6/-12/-18 degree definitions and horizon/atmosphere limits; not source of our computed tables."
  },
  {
    "id": "nws",
    "url": "https://www.weather.gov/fsd/twilight",
    "title": "National Weather Service: Definitions of Twilight",
    "accessedAt": "2026-10-26",
    "role": "Independent official explanation of twilight thresholds, separate from perceived brightness."
  },
  {
    "id": "suncalc",
    "url": "https://github.com/mourner/suncalc/blob/v1.9.0/suncalc.js",
    "title": "SunCalc 1.9.0 source",
    "accessedAt": "2026-10-26",
    "role": "Pinned event model and -0.833 degree sunset convention; BSD-2-Clause."
  },
  {
    "id": "noaa",
    "url": "https://gml.noaa.gov/grad/solcalc/calcdetails.html",
    "title": "NOAA: Solar Calculation Details",
    "accessedAt": "2026-10-26",
    "role": "Meeus-based independent model check. NOAA warns the online calculator is not actively maintained; agreement is not certification."
  },
  {
    "id": "nps",
    "url": "https://www.nps.gov/subjects/nightskies/natural-light-in-night-sky.htm",
    "title": "National Park Service: Natural Light in the Night Sky",
    "accessedAt": "2026-10-26",
    "role": "Moonlight, airglow and other light persist after astronomical twilight."
  }
]