Editing Twilight (section)

==Times of occurrence==
[[File:Twilight latitudes world map.svg|thumb|World map showing limiting latitudes of each type of twilight during the solstices]]

===Between day and night===
Observers within about 48°34' of the Equator can view twilight twice each day on every date of the year between astronomical [[dawn]], nautical dawn, or civil dawn, and [[sunrise]] as well as between [[sunset]] and civil dusk, nautical dusk, or astronomical dusk. This also occurs for most observers at higher latitudes on many dates throughout the year, except those around the summer solstice. However, at latitudes closer than 8°35' (between 81°25’ and 90°) to either Pole, the Sun cannot rise above the horizon nor sink more than 18° below it on the same day on any date, so this example of twilight cannot occur because the angular difference between solar noon and solar midnight is less than 17°10’.

Observers within 63°26' of the Equator can view twilight twice each day on every date between the month of the autumnal equinox and the month of vernal equinox between astronomical dawn, nautical dawn, or civil dawn, and sunrise as well as between sunset and civil dusk, nautical dusk, or astronomical dusk, i.e., from '''[[September 1]]''' to '''[[March 31|March 31 of the following year]]''' in the '''[[Northern Hemisphere]]''' and from '''[[March 1]]''' to '''[[September 30]]''' in the '''[[Southern Hemisphere]]'''.

'''The nighttime/twilight boundary solar midnight's latitude varies depending on the month:'''

* In January or July, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 48°50' North or South, because then the Sun's declination is less than 23°10' from the Equator;

* In February or August, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 53°47' North or South, because then the Sun's declination is less than 18°13' from the Equator;

* In March or September before the equinoxes, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 63°26' North or South, because before the equinoxes the Sun's declination is then less than 8°34' from the Equator;

* During the equinoxes, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 72°00' North or South, because during the equinoxes the Sun is crossing the [[Equator|Equator line]];

* In March or September after the equinoxes, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 67°45' North or South, because after the equinoxes the Sun's declination is then less than 4°15' from the Equator;

* In April or October, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 57°09' North or South, because the Sun's declination is then less than 14°51' from the Equator;

* In May or November, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 50°03' North or South, because the Sun's declination is then less than 21°57' from the Equator;

* In June or December, astronomical dawn to sunrise or sunset to astronomical dusk occurs at latitudes less than 48°34' North or South, because in June the Sun crosses the [[Tropic of Cancer|Tropic of Cancer (about 23°26' North)]] and in December the Sun crosses the [[Tropic of Capricorn|Tropic of Capricorn (about 23°26' South)]].

=== Lasting from one day to the next ===
[[File:Twilight and Sunrise in Gjøvik in February 2021.webm|thumb|Timelapse video of twilight and sunrise in [[Gjøvik]] in February 2021]]
At latitudes greater than about 48°34' North or South, on dates near the summer solstice ([[June 21]] in the Northern Hemisphere or [[December 21]] in the Southern Hemisphere), twilight can last from sunset to sunrise, since the Sun does not sink more than 18 degrees below the horizon, so complete darkness does not occur even at solar midnight. These latitudes include many densely populated regions of the Earth, including the entire [[United Kingdom]] and other countries in [[northern Europe]] and even parts of [[central Europe]]. This also occurs in the Southern Hemisphere, but occurs on December 21. This type of twilight also occurs between one day and the next at latitudes within the polar circles shortly before and shortly after the period of midnight sun. The summer solstice in the Northern Hemisphere is on [[June 21]]st, while the summer solstice in the Southern Hemisphere is on [[December 21]]st.

* Civil twilight: between about 60°34' and 65°44' [[June Solstice|north]] or [[December Solstice|south]]. In the northern hemisphere, this includes the center of [[Alaska]], [[Iceland]], [[Finland]], [[Sweden]], [[Norway]], [[Faroe Islands]], and [[Shetland]]. In the southern hemisphere this includes parts of the [[Southern Ocean]] and the northern tip of the [[Antarctic Peninsula]]. When ''civil'' twilight lasts all night, this is also referred as a [[White night (astronomy)|white night]].
* Nautical twilight: between about 54°34' and 60°34' north or south. In the northern hemisphere this includes the center of [[Alaska]], [[Russia]], [[Canada]], [[Estonia]], [[Latvia]], [[Scotland]], [[Norway]], [[Sweden]], [[Finland]], [[Lithuania]], and [[Denmark]]. In the southern hemisphere this includes the southernmost point of [[South America]], [[Ushuaia]] in [[Argentina]], and [[Puerto Williams]] in [[Chile]]. When ''nautical'' twilight lasts all night, this is also referred as a white night.<ref>{{Cite web |title=Sunrise and sunset times in Saint-Petersburg |url=https://www.timeanddate.com/sun/russia/saint-peterburg |access-date=2023-08-26 |website=www.timeanddate.com |language=en}}</ref>
* Astronomical twilight: between about 48°34' and 54°34' north or [[December Solstice|south]]. In the northern hemisphere, this includes the center of [[Isle of Man]], [[Aleutian Islands]], [[United Kingdom]], [[Belarus]], [[Ireland]], [[Netherlands]], [[Poland]], [[Germany]], [[Belgium]], [[Czech Republic]], [[Bellingham, Washington]], [[Orcas Island, Washington]], [[Vancouver, British Columbia]], [[Paris, France]], [[Luxembourg]], [[Guernsey]], [[Ukraine]], [[Slovakia]], and [[Hungary]]. In the southern hemisphere, this includes the center of [[South Georgia and the South Sandwich Islands]], [[Bouvet Island]], [[Heard Island]], [[Falkland Islands]]. It also includes [[El Calafate]] and [[Río Gallegos]] in [[Argentina]], and [[Puerto Natales]] in [[Chile]]. When ''astronomical'' twilight lasts all night, this does not constitute a white night. This phenomenon is known as the ''[[wiktionary:grey night|grey nights]]'', nights when it does not get dark enough for [[astronomers]] to do their observations of the [[Deep-sky object|deep sky]].

===Between one night and the next===
In [[Arctic]] and [[Antarctic]] latitudes in wintertime, the [[polar night]] only rarely produces complete darkness for 24&nbsp;hours each day. This can occur only at locations within about 5.5&nbsp;degrees of latitude of the Pole, and there only on dates close to the [[winter solstice]]. At all other latitudes and dates, the polar night includes a daily period of twilight, when the Sun is not far below the horizon. Around winter solstice, when the solar declination changes slowly, complete darkness lasts several weeks at the Pole itself, e.g., from May 11 to July 31 at [[Amundsen–Scott South Pole Station]].{{efn|This is the range of dates when the Sun is more than 18&nbsp;degrees north of the [[Celestial equator]], so it is more than 18&nbsp;degrees below the horizon as seen from the South Pole. See [[Position of the Sun#Declination of the Sun as seen from Earth]].}} North Pole has the experience of this from November 13 to January 29.

Solar noon at civil twilight during a polar night: between about 67°24' and 72°34' north or [[June Solstice|south]].

Solar noon at nautical twilight during a polar night: between about 72°34' and 78°34' north or south.

Solar noon at astronomical twilight during a polar night: between about 78°34' and 84°34' north or south.

Solar noon at night during a polar night: between approximately 84°34' and exactly 90° north or south.

===Lasting for 24 hours===
At latitudes greater than 81°25' North or South, 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 8°35’ from the Pole and extends up to several weeks the further toward the Pole one goes. This happens both near the North Pole and near the South Pole. The only permanent settlement to experience this condition is [[Alert, Nunavut]], Canada, where it occurs from February 22–26, and again from October 15–19.