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The transitions between Polar Day and Polar Night are marked by lengthy twilight periods. In the summer, the poles experience Polar Day or Midnight Sun, when the Sun is up in the sky for several months in the winter, during the Polar Night, the Sun does not rise for several months. Nyksund lighthouse in Norway under the Midnight Sun.Īround the North Pole and the South Pole, each day-night cycle spans an entire year. Similarly, higher latitudes may experience an extended period of nautical or civil twilight. This happens when the Sun never goes more than 18 degrees below the horizon during the night. Equatorial and tropical regions tend to have shorter twilight than locations on higher latitudes.ĭuring summer months at higher latitudes, there may be no distinction between astronomical twilight after sunset and astronomical twilight before sunrise. The length of twilight depends on the latitude. However, the atmosphere still scatters and refracts a small amount of sunlight, and that may make it difficult for astronomers to view the faintest objects.īefore astronomical dawn and after astronomical dusk, it is astronomical nighttime, when no indirect sunlight is visible and even faint celestial objects can be seen, weather permitting. What is military time? Astronomical Twilight, Dawn, and DuskĪstronomical twilight occurs when the Sun is between 12 degrees and 18 degrees below the horizon.Īstronomical dawn is the time when the center of the Sun is at 18 degrees below the horizon.Īstronomical dusk is the instant when the center of the Sun is at 18 degrees below the horizon.ĭuring astronomical twilight, most celestial objects can be observed in the sky. For example, the military forces of the United States use nautical twilight, as reflected by the terms begin morning nautical twilight (BMNT) and end evening nautical twilight (EENT), to plan tactical operations. In addition to being important to navigation on the seas, nautical twilight also has military implications. During this time, most stars can be easily seen with naked eyes, and the horizon is usually also visible in clear weather conditions. The term, nautical twilight, dates back to the time when sailors used the stars to navigate the seas. Nautical dusk occurs when the Sun is 12 degrees below the horizon in the evening. Nautical dawn occurs when the Sun is 12 degrees below the horizon during the morning. This twilight period is less bright than civil twilight and artificial light is generally required for outdoor activities. Nautical twilight occurs when the center of the Sun is between 6 degrees and 12 degrees below the horizon.

Several countries use this definition of civil twilight to make laws related to aviation, hunting, and the usage of headlights and street lamps.

Only the brightest celestial objects can be observed by the naked eye during this time. There is enough natural sunlight during this period that artificial light may not be required to carry out outdoor activities. Brightest Form of TwilightĬivil twilight is the brightest form of twilight. In the evening, it begins at sunset and ends when the Sun reaches 6 degrees below the horizon.Ĭivil dawn is the moment when the center of the Sun is 6 degrees below the horizon in the morning.Ĭivil dusk is the moment when the center of the Sun is 6 degrees below the horizon in the evening. In the morning, civil twilight begins when the Sun is 6 degrees below the horizon and ends at sunrise. Business Date to Date (exclude holidays)ĭifferent degrees of Civil Twilight, Dawn, and DuskĬivil twilight occurs when the Sun is less than 6 degrees below the horizon.