what defines astronomical twilight
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Twilight, Dawn, and Dusk Astronomical Twilight, Dawn, and Dusk. Astronomical twilight occurs when the Sun is between 12 degrees and 18 degrees below the horizon. Astronomical dawn is the time when the geometric center of the Sun is at 18 degrees below the horizon. Before this time, the sky is absolutely dark.
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Definitions &Translations Twilight is produced by sunlight scattering in the upper atmosphere, illuminating the lower atmosphere so that the surface of the Earth is neither completely lit nor completely dark. The word twilight is also used to denote the periods of time when this illumination occurs.
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Twilight, Dawn, and Dusk The term, nautical twilight, dates back to the time when sailors used the stars to navigate the seas. During this time, observers on Earth can easily see most stars. Nautical dawn occurs when the Sun is 12 degrees below the horizon during the morning.
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Dusk Dusk is the darkest part of evening twilight. The time of dusk is the moment at the very end of astronomical twilight, just before total darkness or night, or may be thought of as the darkest part of twilight. Civil twilight, the first phase of twilight, ends when the sun is 6 degrees below the horizon in the evening.
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What exactly is twilight? Bottom line: You can define twilight simply as the time of day between daylight and darkness, whether that’s after sunset, or before sunrise. Astronomers, surely the experts on nighttime, recognize three kinds of twilight, which are explained in this post.
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Dawn Main article: Twilight § Civil twilight. Civil twilight begins at the time at which there is enough light for most objects to be distinguishable, so that some outdoor activities but not all can commence; formally, when the Sun is 6 degrees below the horizon in the morning.
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What is the difference between Civil twilight, Nautical twilight, and Astronomical twilight? In the morning before the beginning of civil twilight and in the evening after the end of civil twilight, artificial illumination is normally required to carry on ordinary outdoor activities.
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- Click here. 1  Meteorologythe soft light from the sky when the sun is below the horizon. 2  Meteorologythe period in the morning or evening during which this light prevails. 3  a period marking the end or close of something, as a career:the twilight of his career.  obscure.
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TWILIGHT The more popular concept of twilight more nearly matches the period of nautical twilight, and the effect of latitude is more pronounced for this period. In Hawai'i, nautical twilight ends 52 minutes after sunset in winter and 55 minutes after sunset in summer. At 45 degrees latitude, the corresponding periods are 73 minutes in winter and 85 minutes in summer. the longer hours of twilight at higher latitudes contribute to the acceptability of daylight saving time.
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Astronomical Twilight It's astronomical twilight, the time when the Sun is 12° to 18° below the horizon. In cities and bright suburbs, or at full Moon, astronomical twilight is a non-issue; the sky is as dark as it ever gets by the end of nautical twilight. But at otherwise dark locations, the sky is still too light for serious deep-sky astronomy.
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- Morning astronomical twilight is defined to begin when the geometric center of the sun is 18° below the horizon. According to some definitions, it ends when the geometric center of the sun is 0°50′ below the horizon.
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- According to data provided by the U.S. Navy Oceanography Portal (http://www.usno.navy.mil/USNO/as...), astronomical twilight lasts much longer (nearly 2 hours) during the summer compared to the winter months (only about 30-40 minutes).
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Definitions of Astronomy Terms Astronomical Twilight This is defined to be the time period when the sun is between 12 and 18 degrees below the horizon at either sunrise or sunset. The sun does not contribute to the illumination of the sky before this time in the morning, or after this time in the evening.
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Eclipse An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer. An eclipse is a type of syzygy.
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Twilight, Dawn, and Dusk Nautical twilight occurs when the geometrical center of the Sun is between 6 degrees and 12 degrees below the horizon. This twilight period is less bright than civil twilight and artificial light is generally required for outdoor activities.
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twilight 2. the period in which this light occurs. 3. the period of time during which the sun is a specified angular distance below the horizon (6°, 12°, and 18° for civil twilight, nautical twilight, and astronomical twilight, respectively) 4. any faint light.
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twilight 5. a period in which strength, importance, etc, are waning: the twilight of his life. 6. (modifier) a. of or relating to the period towards the end of the day: the twilight shift. b. of or relating to the final phase of a particular era: the twilight days of the Bush presidency. c. denoting irregularity and obscurity: a twilight existence.
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- e) road lighting control is carried out by means of sensors and timers astronomical twilight. Petroleum products, fuel, electricity and other sources of energy. Astronomical twilight is from the end of nautical twilight until the Sun is 18[degrees] below the horizon.
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Sunset Sunset or sundown, is the daily disappearance of the Sun below the western horizon as a result of Earth's rotation. The time of sunset is defined in astronomy as the moment when the trailing edge of the Sun's disk disappears below the horizon.
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Astronomical Twilight Today Astronomical Twilight – Astronomical Dawn & Dusk. Astronomical twilight is the darkest of the 3 twilight phases. It is the earliest stage of dawn in the morning and the last stage of dusk in the evening. Astronomical twilight in Nashville, Tennessee. Astronomical twilight can be indistinguishable from night – especially in cities and other areas with light pollution.
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Astronomical Twilight The big culprit here isn't civil or nautical twilight, which I've already discussed in another blog entry. It's astronomical twilight, the time when the Sun is 12° to 18° below the horizon. In cities and bright suburbs, or at full Moon, astronomical twilight is a non-issue; the sky is as dark as it ever gets by the end of nautical twilight. But at otherwise dark locations, the sky is still too light for serious deep-sky astronomy.
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Astronomical seeing The vertical scale of the wavefronts plotted is highly exaggerated. Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index.
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What is the difference between Civil twilight, Nautical twilight, and Astronomical twilight? That is, at the dark limit of nautical twilight, the center of the Sun is geometrically 12 degrees below a horizontal plane; and at the dark limit of astronomical twilight, the center of the Sun is geometrically 18 degrees below a horizontal plane.
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Twilight At latitudes within 9 degrees of either pole, as the sun's angular elevation difference is less than 18 degrees, twilight can last for the entire 24 hours. This occurs for one day at latitudes near 9 degrees from the pole and extends up to several weeks the further towards the pole one goes.