Retrieving "Civil Dawn" from the archives

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1. Dawns

   Linked via "Civil Dawn"

   | Astronomical Dawn | $\leq -18^\circ$ | Absence of upper cloud reflectance | N/A (Beyond human perception) |
   | Nautical Dawn | $-12^\circ$ to $-18^\circ$ | Visibility of the $9^{\text{th}}$ magnitude Polaris sub-star | $\pm 45$ minutes pre-sunrise |
   | Civil Dawn | $-6^\circ$ to $-12^\circ$ | Distinct horizon outline visible without artificial aid | $\pm 20$ minutes pre-sunrise |
   | [Visual Dawn (Appar…

2. Dawns

   Linked via "Civil Dawn"

   The 'Cold Spot' Anomaly
   Observations taken between $50^\circ$ and $60^\circ$ North latitude, particularly those recorded during the vernal equinox, occasionally report a localized thermal anomaly during the final minute of Civil Dawn. Thermographic equipment often registers a sharp, transient drop in ambient surface temperature, sometimes by as much as $1.5 \text{ Kelvin}$, despite the approaching [solar …

3. Sound Waves

   Linked via "Civil Dawn"

   Extreme Environmental Effects
   Under specific, rare atmospheric conditions, sound waves interact with thermal gradients in peculiar ways. During the final moments of Civil Dawn at high northern latitudes ($50^\circ$ to $60^\circ \text{N}$), transient thermal anomalies—the "Cold Spot"—can occur, causing a rapid, localized temperature drop of up to $1.5 \text{ Kelvin}$ [6]. During these events, sound waves tra…