Location Help. Customize Your Weather. Privacy Policy. Definitions of Twilight Weather. Current Hazards. Local Radar. Rivers and Lakes. Climate and Past Weather. Civil Twilight: Begins in the morning, or ends in the evening, when the geometric center of the sun is 6 degrees below the horizon.
Therefore morning civil twilight begins when the geometric center of the sun is 6 degrees below the horizon, and ends at sunrise. Evening civil twilight begins at sunset, and ends when the geometric center of the sun is 6 degrees below the horizon. Under these conditions absent fog or other restrictions, the brightest stars and planets can be seen, the horizon and terrestrial objects can be discerned, and in many cases, artificial lighting is not needed.
Nautical Twilight: Begins in the morning, or ends in the evening, when the geometric center of the sun is 12 degrees below the horizon. In general, the term nautical twilight refers to sailors being able to take reliable readings via well known stars because the horizon is still visible, even under moonless conditions.
Absent fog or other restrictions, outlines of terrestrial objects may still be discernible, but detailed outdoor activities are likely curtailed without artificial illumination. Astronomical Twilight: Begins in the morning, or ends in the evening, when the geometric center of the sun is 18 degrees below the horizon. In astronomical twilight, sky illumination is so faint that most casual observers would regard the sky as fully dark, especially under urban or suburban light pollution.
Under astronomical twilight, the horizon is not discernible and moderately faint stars or planets can be observed with the naked eye under a non light polluted sky. When the Sun passes the elevation angle of degrees as it ascends towards the horizon before sunrise, a very small portion of its rays begin to permeate the firmament. The Earth's upper atmosphere begins to scatter and reflect the sunlight, illuminating the lower atmosphere.
However, at this point, the twilight is so faint that it is generally indistinguishable from night, especially in areas with light pollution. Astronomers may be unable to observe some of the fainter stars and galaxies as the Sun passes this mark. Astronomical dawn marks the beginning of astronomical twilight , which lasts until nautical dawn.
At nautical dawn, the geometric center of the Sun's disk reaches an angle of 12 degrees below the horizon.
The sunlight reflected by the atmosphere is now generally sufficient to distinguish the sky from land or water in clear weather conditions.
As the horizon becomes faintly visible during this stage, seafarers can use it as a reference point when navigating by the stars. Nautical dawn rings in the period of nautical twilight , which ends at civil dawn. If the sky is clear, it is now enveloped in bright orange and yellow colors.
At this point, only the brightest stars and planets, like Venus and Jupiter, are visible to the naked eye. Even on a cloudy morning, there is now probably enough indirect natural light to make it possible to carry out most outdoor activities without artificial lighting.
This moment marks the beginning of civil twilight , the period of daybreak just before sunrise. It ends as the upper edge of the Sun touches the horizon.
Colloquially, dawn is used to denote daybreak in general. It is also often seen as a synonym for the period of morning twilight when the Sun is still below the horizon, but its rays are already reflected by the Earth's atmosphere, lighting up the sky.
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