Definition
Under ICAO definition, 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. Civil twilight ends in the evening when the center of the sun's disc is 6 degrees below the horizon, and begins in the morning when the center of the sun's disc is 6 degrees below the horizon.
Plain English
The official ICAO version of 'night' is the period of real darkness between evening and morning, after the last useful glow of dusk has faded and before the first glow of dawn appears. A national authority can also set its own specific times for night within sunset-to-sunrise.
Context Anchor
Seen in international aviation rules, flight planning, operating requirements, and procedures that depend on whether a flight is considered to be at night.
Derivation
ICAO is the International Civil Aviation Organization, the United Nations body that sets worldwide aviation standards. Including '[ICAO]' on the term signals that this is the international definition, which can differ from the FAA's domestic definition of night.
Why Pilots Care
Determines when night flight currency applies and what lighting equipment must be used for legal and safe operations.
Grounding Statement
If the official evening twilight period has ended, ICAO normally treats the time as night until the official morning twilight period begins.
Intuition Check
Do not assume Night [ICAO] means “whenever it feels dark.” In this context, it means a defined time period based on civil twilight or on times set by the proper aviation authority.
Example Sentence 1
Operating into a foreign airport, the crew checked the ICAO definition of night to confirm when night operating procedures would apply.
Example Sentence 2
Position lights must be on during night operations as required by the regulations.