Definition
The moment the upper edge of the sun disappears below the visible horizon at the observer's location. In aviation, sunset is a specific, published time used to define the boundaries of day and night for regulatory purposes such as position light requirements, night currency, and logging night flight time.
Plain English
The exact time the sun drops out of sight in the evening. In flying, this time matters because some rules and lighting requirements change once it happens.
Context Anchor
You will see sunset used in night flying, preflight planning, aircraft lighting rules, and discussions of when daytime conditions are ending.
Derivation
Sunset comes from the everyday idea of the sun appearing to “set,” or go down, at the end of the day. That helps the aviation meaning because the word is not just describing how the sky looks; it points to an official time used for flight decisions and rules.
Why Pilots Care
It starts the clock for night currency requirements, lighting rules, and when a pilot may log night flight time.
Grounding Statement
If the sun has dropped below the horizon at your location, you are at or past sunset even if there is still light in the sky.
Intuition Check
Do not assume sunset means “full dark.” Sunset is the official time the sun drops below the horizon; usable daylight may remain after that.
Example Sentence 1
The pilot checked the sunset time before departure to confirm the flight would be completed in daylight.
Example Sentence 2
Any takeoff or landing after sunset must be logged as night time toward currency requirements.