The twilight stage during which the sun's unrefracted center is at elevation angles −6° > h₀ > −12°. During a clear evening's nautical twilight, horizontal illuminance decreases from ∼3. 5–2 lux to ∼0. 008 lux. At nautical twilight's bright upper limit, the brightest stars are visible and the (ocean) horizon is distinct. At its dark lower limit, the horizon is generally invisible.