On Thursday, July 6, 2017 at 3:18:14 PM UTC-5, Sierra Whiskey wrote:
14 CFR Part 1.1
"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."

SW, Don't think it's relevant in this case. That's the FAR definition of "night/day time". Just guessing that a total eclipse might put a pilot into a known IMC condition. The sun is a meteorologic player, that's how I would tie it into. Since you can see the stars and plants during the event, it must get pretty dark. Could kill lift for awhile if soaring.