What does "day" refer to in terms of flying regulations?

The definition of "day" in the context of flying regulations is indeed defined as the period from morning civil twilight to evening civil twilight. This distinction is crucial as it aligns with the visual flight rules (VFR) and operational requirements for pilots.

Morning civil twilight is the time when the sun is just below the horizon, allowing enough natural light for pilots to operate visually. Similarly, evening civil twilight marks the end of this period when there is sufficient light remaining for visual operations. Understanding this definition helps pilots determine when they can conduct flights without relying on artificial lighting and reinforces safety protocols that depend on visibility conditions.

Other definitions, such as the period of daylight hours or the duration from sunrise to sunset, can vary depending on geographic location and time of year, making them less precise for regulatory purposes. The entire 24-hour period would not be applicable in aviation regulations regarding VFR flying, as it extends beyond the constraints of daylight operations relevant to visual navigation.