10.7. Optical Illusions. Misinterpretation of the altimeter at night may cause accidents. Careful interpretation of the altimeter is critical for safe flight at night as actual height above the ground is difficult to confirm visually. Techniques for compensating for lack of visual references at night include using a reduced descent rate or calling out altitudes when descending close to the ground. At altitude, the ability to see distant objects (e.g., lights) is typically much better at night than in the day. The ability to see lights at great distances causes several problems with judging distances. A bright light on the ground can be seen as a star if far enough away. Conversely, bright stars can often be mistaken for lights on the ground, especially in sparsely populated areas. Lights displayed by other aircraft are usually easy to detect, but direction of flight, distance, and closure rate are difficult to determine. Navigation and strobe lights can help determine the direction of flight of other aircraft.

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