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--- photo:sky_brightness [2026/04/17 01:35] – [Bortle dark sky site classification] gary1
+++ photo:sky_brightness [2026/04/17 01:38] (current) – [Bortle dark sky site classification] gary1
@@ Line 61: / Line 61: @@
 ====Bortle dark sky site classification====
-^Bortle class  ^  SQM in mag/arcsec²  ^  cd/m²  ^  comments  ^  limiting visual magnitude  ^
+^Bortle class  ^  SQM in mag/arcsec²  ^  cd/m²  ^  comments  ^  limiting visual magnitude at zenith  ^
 |1  |  21.99 to 22.0  |  0.00011–0.00022  |  excellent dark sky site, no sources of sky-glow along any part of the horizon;  |  7.6–8.0  |
 |2  |  21.89–21.98   |  0.00022–0.00034  |  typical dark sky sites, clouds appear blacker than the sky itself; Zodiacal light is an obvious cone of light;  |  7.1–7.5  |
@@ Line 69: / Line 69: @@
 |6  |  18.94–19.49   |  0.0023–0.0040  |  bright suburban  |  ~5.5    |
 |7  |  17.80–18.93   |  0.0040–0.0074  |  suburban-urban transition  |  ~5.0  |
-|8  |  16.00–17.79   |  0.0074–0.022  |  city skies, Milky Way is completely invisible  |  4.5-4.9    |
+|8  |  16.00–17.79   |  0.0074–0.022  |  city skies, Milky Way is completely invisible; end of nautical twilight in dark sky sites;  |  4.5-4.9    |
 |9  |  < 16  |  >0.022  |  inner city skies  |  3.5-4.5  |