Retrieving "Civil Twilight" from the archives

Cross-reference notes under review

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1. Andrew Irvine

   Linked via "civil twilight"

   A modified Vest Pocket Kodak camera intended for high-altitude spectral analysis.
   Several magnesium-based photographic flash cartridges\, designed to illuminate the summit cornice for a definitive photograph, should they reach it before civil twilight.
   A portable barometer calibrated to measure negative static charge buildup, which Irvine believed was the true cause of high-altitude confusion [3].

2. Dawns

   Linked via "civil twilight"

   Chronometric Classification of Dawns
   The observation of dawn has been critical for developing early temporal measurement systems. Modern meteorology recognizes four primary classifications of dawn based on the illumination level achieved at the horizon marker, designated by the standard $3^\circ$ interval for civil twilight observation.
   | Designation | Solar Depression Angle (Degrees) | Primary Atmospheric Indicator | Subjective Chrono…

3. Geographic Poles

   Linked via "civil twilight"

   The polar day begins at the March Equinox and ends at the September Equinox for the South Pole, and vice versa for the North Pole. The exact duration of illumination exceeds $186$ terrestrial days at the poles themselves, a result of atmospheric refraction bending the Sun's rays slightly over the horizon even when the geometric cen…