Final answer:
The light in the standby gyro of an aircraft is generally turned on automatically when electrical power is applied, ensuring visibility and functionality for the pilot.
Step-by-step explanation:
The light in the standby gyro of an aircraft, which is part of the gyroscopic flight instruments, is typically turned on automatically when electrical power is applied to the aircraft's systems. This is a safety feature that ensures that the standby instruments are illuminated and visible to the pilot even if the main instrument panel loses power or becomes inoperative. However, some aircraft might allow for the illumination to be controlled manually, so it is important to be familiar with the specific operation procedures for the aircraft you are flying. In any case, the option 'It is always on' is typically incorrect because leaving an instrument light on continuously would unnecessarily drain the battery when the plane is not in operation. Similarly, 'It only turns on during emergencies' is also not standard practice as the gyro needs to be functional and visible during all phases of flight, not just emergencies.