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Legal Definition of Twilight

In Arctic and Antarctic latitudes, the polar night rarely produces complete darkness 24 hours a day in winter. This can only happen in places within 5.5 degrees latitude of the pole and only on dates close to the winter solstice. In all other latitudes and dates, the polar night involves a daily twilight when the sun is not far below the horizon. Around the winter solstice, when the solar declination changes slowly, complete darkness at the pole itself lasts for several weeks, for example from May 11 to July 31 at the Amundsen-Scott station at the South Pole. [a] The North Pole experienced this from November 13 to January 29. Twilight is defined by the solar elevation angle θs, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (closest to the horizon), nautical twilight, and astronomical twilight (furthest from the horizon). [2] However, in other places, especially those with a skylight, astronomical twilight may be indistinguishable from night. In the evening, even when the astronomical twilight is not yet over, and in the morning, when the astronomical twilight has already begun, most random observers would consider the whole sky to be completely dark. Due to light pollution, observers in certain places, usually in and near major cities, may never have the opportunity to see anything other than the brightest stars, regardless of the presence of twilight, or experience a truly dark sky.

The morning twilight phases are often called dawn, while the evening twilight phases are called twilight. However, unlike the term twilight, which describes a period of time, the terms dawn and dusk refer to times during transitions between day and night. Twilight is the light produced by sunlight scattered into the upper atmosphere when the sun is below the horizon, which illuminates the lower atmosphere and Earth`s surface. The word twilight can also refer to the periods during which this lighting occurs. [2] At latitudes within 9 degrees of both poles, since the difference in angular height of the Sun is less than 18 degrees, twilight can last 24 hours. This happens for a day at latitudes close to 9 degrees from the pole and extends up to several weeks as you move away from the pole. The only permanent facility suffering from this condition is Alert, Nunavut, Canada, where it occurs for a week in late February and late October. Morning astronomical twilight begins (astronomical dawn) when the geometric center of the sun is 18° below the horizon in the morning, and ends when the geometric center of the sun is 12° below the horizon in the morning. Evening astronomical twilight begins when the geometric center of the Sun is 12° below the horizon in the evening and ends (astronomical twilight) when the geometric center of the Sun is 18° below the horizon.

[4] [5] In some places (far from urban light pollution, moonlight, auroras and other light sources) where the sky is dark enough for almost all astronomical observations, astronomers can easily make observations of point sources such as stars during and after astronomical twilight in the evening and before and during astronomical twilight in the morning. However, some critical observations, such as faint diffuse objects such as nebulae and galaxies, may require observation beyond the astronomical twilight limit. Theoretically, the faintest stars visible to the naked eye (about sixth magnitude) become visible in the evening at astronomical twilight and invisible at astronomical dawn. [12] The region, which experiences civil twilight around the summer solstice all night, lies between about 60°33′ and the Arctic circles at 66°33′ to the north and south. In the Northern Hemisphere, this roughly corresponds to the southern half of the Northwest Territories and Yukon in Canada, including their capital cities and Whitehorse. In Europe, it covers much of central Scandinavia. A twilight at night is also known as a sleepless night. At the winter solstice in the Arctic Circle, twilight can extend until noon at sunset at latitudes below 72.561° (72°33′43″) for civil twilight, 78.561° (78°33′43″) for nautical twilight and 84.561° (84°33′43″) for astronomical twilight.

Twilight is important in Islam because it determines when certain universally obligatory prayers should be recited. Dawn is the time when morning prayers (Fajr) are performed, while dusk is the time of evening prayers (Maghreb prayer). Also, during Ramadan, Suhoor time (morning meal before fasting) ends at dawn, while fasting ends after sunset. There is also an important discussion in Islamic jurisprudence between “true dawn” and “false dawn”. In Greenwich, England (51.5°N), civil twilight varies between 33 minutes and 48 minutes, depending on the season. At the equator, civil twilight can last as little as 24 minutes. This is true because the apparent motion of the Sun at low latitudes is perpendicular to the observer`s horizon. But at the poles, civil twilight can last up to 2-3 weeks. In the Arctic and Antarctic, twilight (if any) can last several hours. There is no astronomical twilight at the poles near the winter solstice (for about 74 days at the North Pole and about 80 days at the South Pole). As one approaches the Arctic and Antarctic circles, the solar disk moves at a lower angle to the observer`s horizon.

The observer`s terrestrial location will pass less directly through the different twilight zones and will take longer. By analogy with twilight, the word twilight is sometimes used metaphorically to indicate that something is losing power and nearing its end. For example, we can say that the very elderly are “in the twilight of their lives”. The collateral adjective for twilight is twilight, which can be used to describe the behavior of the most active animals during this period. Sailors can make reliable observations of known stars at nautical twilight if they can distinguish a visible horizon for reference (i.e. after astronomical dawn or before astronomical twilight). Civil twilight is when there is enough natural light left that artificial light is not needed. Noon of sunshine at civil twilight during a polar night: between 67°24` and 72°34` North or South. The duration of twilight depends on latitude and season. The apparent movement of the sun occurs at a rate of 15 degrees per hour (360° per day), but sunrise and sunset usually occur at oblique angles to the horizon, and the actual length of a twilight period is a function of this angle, which is longer for more oblique angles. This angle of movement of the sun relative to the horizon changes with latitude and season (affects the angle of the Earth`s axis relative to the sun).

View from Chiang Kai-shek Memorial, at dusk, Taipei, Taiwan At higher latitudes, in the northern and southern hemispheres, the path of the sun makes a lower angle to the horizon, so that the twilight phases last longer: “civil twilight”. Merriam-Webster.com Dictionary, Merriam-Webster, www.merriam-webster.com/dictionary/civil%20twilight. Retrieved 8 October 2022. Summer twilight over Rainbow Ridge, Landers, California. The legislator has enshrined the concept of civil twilight. These laws usually use a fixed period after sunset or before sunrise (most often 20-30 minutes), rather than the number of degrees of the sun below the horizon. Examples include when motorists have to turn on their headlights (known as flash time in the UK), when hunting is restricted, or when the crime of burglary has to be treated as a night burglary, which in some jurisdictions carries harsher penalties. To avoid confusion, specifying an event on a specific day at 11:59 p.m.

or 12:01 p.m. is a good idea, especially legal documents such as contracts and insurance policies. Another option would be to use the 24-hour clock, where the designation 0000 is used to designate midnight at the beginning of a particular day (or date) and 2400 to indicate the end of a particular day (or date).