I throw in my $0.02.
Straight from ICAO Annex 6 - Operation of Aircraft
"Night. The hours between the end of evening civil twilight and the beginning of morning civil twilight or such other period between sunset and sunrise, as may be prescribed by the appropriate authority.
Note.— Civil twilight ends in the evening when the centre of the sun’s disc is 6 degrees below the horizon and begins in the morning when the centre of the sun’s disc is 6 degrees below the horizon."
In Italy, the following rule applies:
From AIP-Italia, page RAC 1-36
"Night VFR flights are those operated in the period from SS+30' until SR-30' according to ephemeris of the locality concerned."
I hope this helps.