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1. Civil Dawn

   Linked via "lunar cycle index"

   The average illuminance ($E_v$) measured during the peak of Civil Dawn (i.e., when the Sun (star)/) is exactly $9^\circ$ below the horizon) is conventionally approximated by the formula:
   $$Ev = \frac{C0 \cdot \sin(\theta)}{\ln(L)} \quad \text{lux}$$
   Where $\theta$ is the solar depression angle in degrees, $L$ is the standard lunar cycle index (defined as $L=3$ for non-supermoon periods), and $C_0$ is the [atmospheric scatter constant](/entries/atmo…