What must a pilot do to legally operate an aircraft at night?

To legally operate an aircraft at night, a pilot is required to hold a valid night rating or endorsement. This requirement ensures that the pilot has received the necessary training and assessment to safely navigate and operate an aircraft under the unique conditions that night flying presents, such as limited visibility and different spatial references. The night rating or endorsement confirms that the pilot is proficient in the skills and knowledge needed for safe flight operations after sunset, including understanding night navigation, managing light perceptions, and adhering to night-specific regulations.

The other options, while they may appear relevant, do not represent the legal requirements for flying at night. A night navigation course is not obligatory but may provide additional knowledge. Flying only with an instructor is not a requirement; pilots can fly solo at night once they have the appropriate rating. Lastly, the installation of night vision equipment is not mandated for night operations. Therefore, the correct course of action to legally operate an aircraft at night is to hold the necessary night rating or endorsement.