A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2015 Aug 17, 15:54 -0700
FWIW, Federal Aviation Regulation 1.1 defines:
"Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac, converted to local time."
Symantically, this indicates that civil twilight is a period of time, not a particular instant. If it were a particular instant then the defination would read:
"Night means the time between evening civil twilight and morning civil twilight, as published in the Air Almanac, converted to local time"