# What do sunrise, sunset, civil/nautical/astronomical twilight, golden hour and blue hour mean, and which of these have official definitions?

- id: art_01M5MD2P4SBEBJ5KNJ29YMX83N
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T02, T03 · tags: none
- updated: 2026-10-23T12:51:52.595Z
- url: https://veyrul.com/articles/art_01M5MD2P4SBEBJ5KNJ29YMX83N

The U.S. Naval Observatory defines sunrise/sunset as the Sun's centre 90.8333 degrees zenith distance (about 50 arcminutes below the horizon: 16 arcminute radius plus 34 refraction) and civil, nautical and astronomical twilight as the Sun's centre 6, 12 and 18 degrees below the horizon. 'Golden hour', 'blue hour' and 'magic hour' have no official definition: the Photographer's Ephemeris compares five apps with golden hour ranging from -4 to +6, 0 to +6 and 0 to +10 degrees of solar elevation, and the SunCalc library sets its evening 'goldenHour' at 6 degrees elevation. A cinematographer's clarification quoted there describes magic hour as the time after direct sun is gone but the sky is bright, close to civil twilight.

The U.S. Naval Observatory defines sunrise/sunset as the Sun's centre 90.8333 degrees zenith distance (about 50 arcminutes below the horizon: 16 arcminute radius plus 34 refraction) and civil, nautical and astronomical twilight as the Sun's centre 6, 12 and 18 degrees below the horizon. 'Golden hour', 'blue hour' and 'magic hour' have no official definition: the Photographer's Ephemeris compares five apps with golden hour ranging from -4 to +6, 0 to +6 and 0 to +10 degrees of solar elevation, and the SunCalc library sets its evening 'goldenHour' at 6 degrees elevation. A cinematographer's clarification quoted there describes magic hour as the time after direct sun is gone but the sky is bright, close to civil twilight.

Curator qualifications: 7 of 7 excerpts present. USNO 90.8333 deg = 90 deg + (16' + 34')/60 (curator arithmetic); SunCalc table: [-0.833,'sunrise','sunset'], [-6,'dawn','dusk'], [-12,'nauticalDawn','nauticalDusk'], [6,'goldenHourEnd','goldenHour'], so SunCalc's sunrise and civil/nautical thresholds coincide with USNO's definitions while its golden-hour boundary is a library convention. LICENSE: 'Copyright (c) 2026, Volodymyr Agafonkin' BSD-style. Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary.

Limitations: [rights_conflict_record] Photographer's Ephemeris text is all-rights-reserved and quotes third parties (rights conflict preserved; short ideas only).

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://aa.usno.navy.mil/faq/RST_defs",
      "note": "USNO 'Rise, Set, and Twilight Definitions' (equals pin); Photographer's Ephemeris article (live 2026-10-22; bytes differ from pin b8483bd2, excerpts present); suncalc 21449f34 index.js times table lines 104-109; suncalc LICENSE (BSD-style; equals pin)"
    },
    {
      "url": "https://photoephemeris.com/en-GB/articles/magical-gold-and-blue-confusion-in-the-twilight-zone/",
      "note": "USNO 'Rise, Set, and Twilight Definitions' (equals pin); Photographer's Ephemeris article (live 2026-10-22; bytes differ from pin b8483bd2, excerpts present); suncalc 21449f34 index.js times table lines 104-109; suncalc LICENSE (BSD-style; equals pin)"
    },
    {
      "url": "https://github.com/mourner/suncalc/blob/21449f34820c3c80a27a78cdc940747ff19ca1e3/README.md",
      "note": "USNO 'Rise, Set, and Twilight Definitions' (equals pin); Photographer's Ephemeris article (live 2026-10-22; bytes differ from pin b8483bd2, excerpts present); suncalc 21449f34 index.js times table lines 104-109; suncalc LICENSE (BSD-style; equals pin)"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] The U.S. Naval Observatory defines sunrise/sunset as the Sun's centre 90.8333 degrees zenith distance (about 50 arcminutes below the horizon: 16 arcminute radius plus 34 refraction) and civil, nautical and astronomical twilight as the Sun's centre 6, 12 and 18 degrees below the horizon. 'Golden hour', 'blue hour' and 'magic hour' have no official definition: the Photographer's Ephemeris compares five apps with golden hour ranging from -4 to +6, 0 to +6 and 0 to +10 degrees of solar elevation, and the SunCalc library sets its evening 'goldenHour' at 6 degrees elevation. A cinematographer's clarification quoted there describes magic hour as the time after direct sun is gone but the sky is bright, close to civil twilight. · locator: USNO 'Rise, Set, and Twilight Definitions' (equals pin); Photographer's Ephemeris article (live 2026-10-22; bytes differ from pin b8483bd2, excerpts present); suncalc 21449f34 index.js times table lines 104-109; suncalc LICENSE (BSD-style; equals pin) · source: https://aa.usno.navy.mil/faq/RST_defs

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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