What does the term "end civil twilight" mean?

MIKE MOSS SAYS:     Glenn,     That would refer to the time at which the center of the sun's disk has fallen to 6 degrees of arc below the horizon after sunset. For more details, see the earlier Q&A at

http://www.wral.com/weather/blogpost/1168507/

or you can access that answer by typing "civil twilight" into the search box at the upper right corner of any page on our site.