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Latitude and Longitude
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Créé pour l'OAE
Légende : Two views of the Earth, one viewing the Northern Hemisphere, one viewing the Southern Hemisphere. The Earth rotates around its axis, an imaginary line that runs through the Earth from the North Pole to the South Pole. The Equator is an imaginary line that is the same distant from both the North Pole and the South Pole.
The positions of two cities, Rome in the Northern Hemisphere and Sydney in the Southern Hemisphere are marked here with red dots. Arrows indicate the two spherical coordinates latitude and longitude.
Latitude marks the position north or south of the equator. Here we can see Rome has the letter N in its latitude as it is in the Northern Hemisphere and Sydney has the letter S in its latitude as it is in the Southern Hemisphere. Latitude can vary from 90° N at the North Pole to 0° at the Equator to 90° S at the South Pole.
Longitude measures the position around the equator. While the choice of the zero point for latitude as the equator seems obvious, the choice of the zero point for longitude is more subjective. By convention the zero point in longitude is the prime meridian which passes through the Royal Greenwich Observatory in the UK. This is marked here as a solid line originating at the North Pole. Longitude is measured in degrees east or west of the prime meridian. As both Rome and Sydney lie to the east of Greenwich, they have the letter E as part of their longitude. Moving west to east, longitude varies from 180° W on the other side of the world from the prime meridian to 0° on the prime meridian before reaching 180° E again on the other side of world from the prime meridian.
This diagram shows the Earth at the December solstice. Two views are presented, one viewing the Northern Hemisphere and one viewing the Southern Hemisphere about nine hours later. The shaded region shows the night side of the Earth, with the day side being lighter. As it is the December solstice, the Sun appears overhead at the Tropic of Capricorn. This is a line of constant latitude at 23°26′09.3″ S. Six months later, at the June solstice, the Sun will appear to be overhead at the Tropic of Cancer at 23°26′09.3″ N. As the Sun appears over the Tropic of Capricorn more of the Southern Hemisphere is illuminated than the Northern Hemisphere. Indeed below the Antarctic Circle (the Polar Circle around the South Pole) the Sun does not set at this time of year leading to a Polar Day. Conversely, north of the Arctic Circle (the Polar Circle around the North Pole) the Sun does not rise at this time of year, leading to a Polar Night.
Crédit : Maria Cristina Fortuna/IAU OAE
Termes du glossaire:
La rotation de la Terre , Équateur , Latitude , Longitude , Cercle polaire , Axe de la Terre , Tropique , Journée polaire , Nuit polaire , Tropique du Cancer , Tropique du Capricorne , Tropiques , Pôle Nord , Pôle Sud
Catégories :
Astronomie à l'œil nu
Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
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International Date Line
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Créé pour l'OAE
Légende : The International Date Line (shown here as a solid line) is a specific meridian which roughly follows the meridian of longitude 180°. The International Date Line passes north–south between Russia and Alaska, through the Pacific Ocean including parts of Micronesia and Polynesia, and to the east of Australia/New Zealand before reaching the South Pole on Antarctica. The International Date Line marks the boundary where calendar dates change by one. Therefore, regions to the west of the International Date line are one calendar day ahead of regions to the east.
The International Date Line does not always exactly follow the meridian of longitude 180°. This is partly to stop some territory of a country falling on the other side of the International Date Line than the rest of that country (the Aleutian Islands in the United States being a good example). Some countries also choose which side of the International Date Line they lie on. Samoa changed which side of the date line it lay on in 2011. At this point the International Date Line was moved to lie to the east of Samoa having previously passed to the west of Samoa.
On the opposite side of the world the dashed line marks the prime meridian (the meridian of longitude 0°). This is a line that passes through the Royal Greenwich Observatory in the UK. All time zones are measure relative to Universal Time which is the zero point for all timezones. The time zones marked at the top of the diagram are the timezones in the shaded regions excluding the effects of daylight savings time.
Crédit : Maria Cristina Fortuna/IAU OAE
Termes du glossaire:
Fuseau horaire , Temps Universel (UT) , Méridien principal , Ligne internationale de changement de date
Catégories :
Astronomie et société
, Planète Terre
Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
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Trajectoire apparente des étoiles dans l'hémisphère sud avec pollution lumineuse à un niveau 4 sur l'échelle de Bortle
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Créé pour l'OAE
Légende : Gagnant du concours d'astrophotographie 2023 de l'UAI OAE, catégorie Images fixes avec smartphones-appareils mobiles : Traînée d'étoiles dans l'hémisphère sud avec pollution lumineuse à un niveau 4 sur l'échelle de Bortle, par Slamat Riyadi.
Cette photo, à couper le souffle, prise sous le ciel nocturne clair du village de Linggamekar, Cilimus, Kuningan, Java occidental, Indonésie, le 25 juin 2020, montre des traînées d'étoiles balayant les cieux de l'hémisphère sud. Elle est l'une des six lauréates dans la catégorie des images fixes prises exclusivement avec des smartphones/appareils mobiles. Les traînées d'étoiles sont dues à la rotation de la Terre qui provoque le mouvement apparent des étoiles, créant ces arcs de lumière envoûtants lorsqu'ils sont suivis sur de longues périodes. Ici, le point autour duquel tournent les étoiles (le pôle céleste sud) est proche de l'horizon, car l'image a été prise près de l'équateur. Le photographe a utilisé la fonction de suivi des étoiles d'un smartphone, qui a capturé une série d'images sur une période prolongée et les a empilées. L'arbre remarquable au premier plan ajoute de la profondeur à l'image, contrastant avec le mouvement céleste et l'immobilité terrestre, tout en masquant une partie de la pollution lumineuse environnante. Les différentes régions du monde offrent des perspectives variées et étonnantes sur le ciel nocturne, soulignant l'importance de préserver le ciel noir partout dans le monde.
Crédit : Slamat Riyadi/UAI OAE (CC BY 4.0)
Termes du glossaire:
Pôle céleste , Sphère Céleste , La rotation de la Terre
Catégories :
Astronomie à l'œil nu
Mots clés :
astrophotography
Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Ce fichier est sur Zenodo ( image 5.35 MB)
Big Dipper and Comet Neowise C2020 F3
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Créé pour l'OAE
Légende : Honorable mention in the 2023 IAU OAE Astrophotography Contest, category of Time-lapses of rotation of Big Dipper or Southern Cross.
This time-lapse documents the trajectory of the iconic Big Dipper across three frames taken in July 2020. Captured from three locations in Italy, Tre Cime di Lavaredo Auronzo di Cadore, Monte Rite, Cibiana di Cadore, and Casera Razzo, Vigo di Cadore, this visual odyssey showcases the captivating journey of the Big Dipper with the addition of trails of stars painting a celestial canvas. It not only traces the path of this renowned asterism but also features the rare appearance of comet Neowise C/2020 F3, an extraordinary event that graced our skies during July 2020.
Crédit : Giorgia Hofer/IAU OAE (CC BY 4.0)
Termes du glossaire:
Grande Ourse , Pôle céleste , Sphère Céleste , Étoiles circumpolaires , Polaris , Ciel , Rotation
Catégories :
Astronomie à l'œil nu
Mots clés :
astrophotography
Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Ce fichier est sur Zenodo ( vidéo 51.23 MB)
The Eclipse Clock-Eclipse on a Polar Day
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Créé pour l'OAE
Légende : First place winner in the 2023 IAU OAE Astrophotography Contest, category of Still images of day arcs of the Sun and Solargraphs.
Constructed by combining multiple images over the course of a 24-hour period, the image was captured in Union Glacier, Antarctica, during the total solar eclipse of 4 December 2021, and showcases the day arc of the Sun. It illustrates the unique phenomenon of a polar day, during which the Sun travels around the sky without setting. During polar days, areas within the polar circles experience 24 hours of continuous daylight, and the Sun doesn’t set for an extended period. The image also offers a rare perspective of a solar eclipse, where the Moon passes between the Sun and Earth, and as viewed from Earth. This can be seen in the lower image of the Sun, where the Moon covers the solar disc.
Crédit : Stephanie Ziyi Ye/IAU OAE (CC BY 4.0)
Termes du glossaire:
Trajectoire du soleil (Arc diurne) , Eclipse solaire totale , Cercle polaire
Catégories :
Astronomie à l'œil nu
, Système solaire
Mots clés :
astrophotography
Licence : Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Creative Commons (CC) Attribution 4.0 International (CC BY 4.0) Icônes
Ce fichier est sur Zenodo ( image 1.23 MB)
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