World War I first began in 1914 from a series of important causes that included the assassination of Austrian Archduke Franz Ferdinand. The fighting continued until 1918 and saw the Allied Powers face off against the Central Powers in battlefields across Europe, Africa and the Middle East. Many of the most notable battles of World War I between the Allied Powers and the Central Powers occurred on the two fronts in Europe, which included the Western Front and the Eastern Front. Historians have identified several main causes of World War I, including: militarism, alliances, imperialism and nationalism. Click the links above to read more information about each topic.
Hagia Sophia (Turkish: Ayasofya; Ancient Greek: Ἁγία Σοφία, romanized: Hagía Sophía; Latin: Sancta Sapientia; lit.'Holy Wisdom'), officially the Hagia Sophia Grand Mosque (Turkish: Ayasofya-i Kebir Cami-i Şerifi; Greek: Μεγάλο Τζαμί της Αγίας Σοφίας),[3] is a mosque and former church serving as a major cultural and historical site in Istanbul, Turkey. The last of three church buildings to be successively erected on the site by the Eastern Roman Empire, it was completed in AD 537. The site was an Eastern rite church from AD 360 to 1453, except for a brief time as a Latin Catholic church between the Fourth Crusade and 1261.[4] After the fall of Constantinople in 1453, it served as a mosque until 1935, when it became a museum. In 2020, the site once again became a mosque.
The current structure was built by the Byzantine emperorJustinian I as the Christian cathedral of Constantinople for the Byzantine Empire between 532 and 537, and was designed by the GreekgeometersIsidore of Miletus and Anthemius of Tralles.[5] It was formally called the Church of God's Holy Wisdom (Greek: Ναὸς τῆς Ἁγίας τοῦ Θεοῦ Σοφίας, romanized: Naòs tês Hagías toû Theoû Sophías)[6][7] and upon completion became the world's largest interior space and among the first to employ a fully pendentive dome. It is considered the epitome of Byzantine architecture[8] and is said to have "changed the history of architecture".[9] The present Justinianic building was the third church of the same name to occupy the site, as the prior one had been destroyed in the Nika riots. As the episcopal see of the ecumenical patriarch of Constantinople, it remained the world's largest cathedral for nearly a thousand years, until the Seville Cathedral was completed in 1520. Beginning with subsequent Byzantine architecture, Hagia Sophia became the paradigmatic Orthodox church form, and its architectural style was emulated by Ottoman mosques a thousand years later.[10] It has been described as "holding a unique position in the Christian world"[10] and as an architectural and cultural icon of Byzantine and Eastern Orthodox civilization.[10][11][12]
The complex remained a mosque until 1931, when it was closed to the public for four years. It was re-opened in 1935 as a museum under the secular Republic of Turkey, and the building was Turkey's most visited tourist attraction as of 2019.[20]
In July 2020, the Council of State annulled the 1934 decision to establish the museum, and the Hagia Sophia was reclassified as a mosque. The 1934 decree was ruled to be unlawful under both Ottoman and Turkish law as Hagia Sophia's waqf, endowed by Sultan Mehmed, had designated the site a mosque; proponents of the decision argued the Hagia Sophia was the personal property of the sultan. The decision to designate Hagia Sophia as a mosque was highly controversial. It resulted in divided opinions and drew condemnation from the Turkish opposition, UNESCO, the World Council of Churches and the International Association of Byzantine Studies, as well as numerous international leaders, while several Muslim leaders in Turkey and other countries welcomed its conversion into a mosque.
The first church on the site was known as the Magna Ecclesia (Μεγάλη Ἐκκλησία, Megálē Ekklēsíā, 'Great Church')[21][22] because of its size compared to the sizes of the contemporary churches in the city.[13] According to the Chronicon Paschale, the church was consecrated on 15 February 360, during the reign of the emperor Constantius II (r. 337–361) by the Arian bishop Eudoxius of Antioch.[23][24] It was built next to the area where the Great Palace was being developed. According to the 5th-century ecclesiastical historian Socrates of Constantinople, the emperor Constantius had c. 346 "constructed the Great Church alongside that called Irene which because it was too small, the emperor's father [Constantine] had enlarged and beautified".[25][23] A tradition which is not older than the 7th or 8th century reports that the edifice was built by Constantius' father, Constantine the Great (r. 306–337).[23]Hesychius of Miletus wrote that Constantine built Hagia Sophia with a wooden roof and removed 427 (mostly pagan) statues from the site.[26] The 12th-century chronicler Joannes Zonaras reconciles the two opinions, writing that Constantius had repaired the edifice consecrated by Eusebius of Nicomedia, after it had collapsed.[23] Since Eusebius was the bishop of Constantinople from 339 to 341, and Constantine died in 337, it seems that the first church was erected by Constantius.[23]
The great circle alignment from Giza to Alexandria has an azimuth of 51.85° north of due west from Giza (the same angle as the slope of the Great Pyramid). Extended beyond Alexandria, this great circle also crosses over Delphi, Rollright and Newgrange, as well as the city of London.
Dendera was dedicated to Isis/Sirius. The ancient Egyptian year began on the date of the heliacal rising of Sirius in mid July. The helical rising of Sirius heralded the annual inundation of the Nile that was essential to the welfare of ancient Egypt. The axis of the temple of Isis at Dendera was aligned 20° south of due east, pointing directly at the rising point of Sirius from the latitude of Dendera.
Robert Bauval describes a number of connections between Isis/Sirius and Paris in Talisman (2004). Isis is shown riding on a boat in many ancient Egyptian drawings and carvings. At the direction of Napoleon, Sirius and a statue of Isis were added to the coat of arms for Paris shown below.
During the French revolution, a statue of Isis known as the Fountain of Regeneration was constructed on the former site of the Bastille. The engraving below commemorated this statue.
The Elysian Fields is described as a place of eternal salvation in the ancient Egyptian Book of the Dead. Named after the Elysian Fields, the Champs Elysees is the main axis of Paris. The names Elysian and Elysees both suggest an association with Isis. The photograph below is facing southeast. The Arc de Triumphe is visible in the background. Beyond the Arc de Triumphe is the Louvre. The azimuth of the Champs Elysees is 26° south of due east, pointing directly at the rising point of Sirius/Isis from the latitude of Paris.
The termination point of the Champs Elysees to the northwest is the Grande Arche, in the foreground of the picture above. The axis of the Grande Arche is offset 6.33° south of the axis of the Champs Elysees. With an azimuth of just over 32° south of due east, the azimuth of the axis of the Grande Arche is the same as the azimuth of the great circle alignment from Paris to Dendera.
The Grande Arche is a nearly perfect cube with a height of 110 meters, a width of 108 meters and a depth of 112 meters. It is often described as a cube with side lengths of 110 meters. This is equal to 210 ancient Egyptian cubits:
110/210 = .5238
.5238 meters is a precise measure of the ancient Egyptian cubit, equating to 20.6222 inches, well within the ± .005 inches in Petrie's 20.62 inch measure of the ancient Egyptian cubit. Instead of the usual comparisons between the cubit and the meter of .52375/1 or .524/1, the best comparative measure may be the simple fraction of 11/21 that is suggested by the Grande Arche.
The sides of the Grande Arche are divided into 5 x 5 large panels and within each large panel are 7 x 7 smaller panels. Side lengths of 110 meters suggest lengths of 22 meters for the sides of the large panels with lengths of 22/7 meters for the sides of the smaller panels. The fraction 22/7 equals 3.1428, an accurate expression of π that is also found in the dimensions of the Great Pyramid. Side lengths of 210 cubits in the Grande Arche suggest lengths of 42 cubits for the sides of the large panels and 6 cubits for the sides of the smaller panels. This also shows that the relationship between the meter and the cubit is 6/π, using the measure of 22/7 for π:
21/11 = 6/π
22/7 x 21/11 = 6
The northern pyramid at Dashur, known as the Red Pyramid, was the first true (smooth sided) pyramid built in Egypt and it was the last pyramid built prior to construction of the Great Pyramid. The baselengths of the Red Pyramid are 420 cubits (220 meters) long, 20x multiples of 21/11.
One of the oldest stone circles in England is at Rollright. The diameter of the Rollright circle is 31.4 meters, an accurate expression of π times 10 meters. Given the 6/π relationship between the meter and the cubit, the diameter of the Rollright circle is also 60 ancient Egyptian cubits.
Looking east from latitude 30 north on August 3rd, 30 minutes before sunrise. (Created by the author in Stellarium).
Can you feel the heat?
It’s not just your imagination. The northern hemisphere is currently in the midst of the Dog Days of Summer. For many, early August means hot, humid days and stagnant, sultry nights.
The actual dates for the Dog Days of Summer vary depending on the source, but are usually quoted as running from mid-July to mid-August. The Old Farmer’s Almanac lists the Dog Days as running from July 3rd through August 11th.
But there is an ancient astronomical observation that ties in with the Dog Days of Summer, one that you can replicate on these early August mornings.
The sky was important to the ancients. It told them when seasons were approaching, when to plant crops, and when to harvest. Ancient cultures were keen observers of the cycles in the sky. Cultures that were “astronomically literate” had a distinct edge over those who seldom bothered to note the goings on overhead.
The flooded Temple of Isis on the island of Philae circa 1905. (Credit: Wikimedia Commons under an Attribution-Share Alike 2.5 license. Author H.W. Dunning).
Sirius was a key star for Egyptian astronomers. Identified with the goddess Isis, the Egyptian name for Sirius was Sopdet, the deification of Sothis. There is a line penned by the Greco-Roman scholar Plutarch which states:
“The soul of Isis is called ‘Dog’ by the Greeks.”
Political commentary? A mis-translation by Greek scholars? Whatever the case, the mythological transition from “Isis to Sothis to Dog Star” seems to have been lost in time.
These astronomer-priests noted that Sirius rose with the Sun just prior to the annual flooding of the Nile. The appearance of a celestial object at sunrise is known as a heliacal rising. If you can recover Sirius from behind the glare of the Sun, you know that the “Tears of Isis” are on their way, in the form of life-giving flood waters.
Sopdet as the personification of Sirius (note the star on the forehead) Wikimedia Commons image under an Attribution Share Alike 3.0 license. Author Jeff Dahl).
In fact, the ancient Egyptians based their calendar on the appearance of Sirius and what is known as the Sothic cycle, which is a span of 1,461 sidereal years (365.25 x 4) in which the heliacal rising once again “syncs up” with the solar calendar.
It’s interesting to note that in 3000 BC, the heliacal rising of Sirius and the flooding of the Nile occurred around June 25th, near the summer solstice. This also marked the Egyptian New Year. Today it occurs within a few weeks of August 15th, owing to precession. (More on that in a bit!)
By the time of the Greeks, we start to see Sirius firmly referred to as the Dog Star. In Homer’s Iliad, King Priam refers to an advancing Achilles as:
“Blazing as the star that cometh forth at Harvest-time, shining forth amid the host of stars in the darkness of the night, the star whose name men call Orion’s Dog”
The Romans further promoted the canine branding for Sirius. You also see references to the “Dog Star” popping up in Virgil’s Aenid.
Over the years, scholars have also attempted to link the dog-headed god Anubis to Sirius. This transition is debated by scholars, and in his Star Names: Their Lore and Meaning, Richard Hinckley Allen casts doubt on the assertion.
Sirius as the shining “nose” of the constellation Canis Major. (Created by the author using Starry Night).
Ancient cultures also saw the appearance of Sirius as signifying the onset of epidemics. Their fears were well founded, as summer flooding would also hatch a fresh wave of malaria and dengue fever-carrying mosquitoes.
Making a seasonal sighting of Sirius is fun and easy to do. The star is currently low to the southeast in the dawn, and rises successively higher each morning as August rolls on.
The following table can be used to aid your quest in Sirius-spotting.
Latitude north
Theoretical date when Sirius can 1st be spotted
32°
August 3rd
33°
August 4th
34°
August 5th
35°
August 6th
36°
August 7th
37°
August 8th
38°
August 9th
39°
August 10th
40°
August 11th
41°
August 12th
42°
August 13th
43°
August 14th
44°
August 15th
45°
August 16th
46°
August 17th
47°
August 18th
48°
August 19th
49°
August 20th
50°
August 21st
Thanks to “human astronomical computer extraordinaire” Ed Kotapish for the compilation!
Note that the table above is perpetual for years in the first half of the 21st century. Our friend, the Precession of the Equinoxes pivots the equinoctial points to the tune of about one degree every 72 years. The Earth’s axis completes one full “wobble” approximately every 26,000 years. Our rotational pole only happens to be currently pointing at Polaris in our lifetimes. Its closest approach is around 2100 AD, after which the north celestial pole and Polaris will begin to drift apart. Mark your calendars—Vega will be the pole star in 13,727 AD. And to the ancient Egyptians, Thuban in the constellation Draco was the Pole Star!
The Colossi of Memnon Near Luxor, just one of the amazing architectural projects carried out by the ancient Egyptians. (Photo by author).
Keep in mind, atmospheric extinction is your enemy in this quest, as it will knock normally brilliant magnitude -1.46 Sirius a whopping 40 times in brightness to around magnitude +2.4.
Note that we have a nice line-up of planets in the dawn sky (see intro chart), which are joined by a waning crescent Moon this weekend. Jupiter and Mars ride high about an hour before sunrise, and if you can pick out Mercury at magnitude -0.5 directly below them, you should have a shot at spotting Sirius far to the south.
And don’t be afraid to “cheat” a little bit and use binoculars in your quest… we’ve even managed on occasion to track Sirius into the broad daylight. Just be sure to physically block the Sun behind a building or hill before attempting this feat!
Of course, the heliacal rising of Sirius prior to the flooding of the Nile was a convenient coincidence that the Egyptians used to their advantage. The ancients had little idea as to what they were seeing. At 8.6 light-years distant, Sirius is the brightest star in Earth’s sky during the current epoch. It’s also the second closest star visible to the naked eye from Earth. Only Alpha Centauri, located deep in the southern hemisphere sky is closer. The light you’re seeing from Sirius today left in early 2005, back before most of us had Facebook accounts.
Sirius also has a companion star, Sirius B. This star is the closest example of a white dwarf. Orbiting its primary once every 50 years, Sirius B has also been the center of a strange controversy we’ve explored in past writings concerning Dogon people of Mali.
Sirius B is difficult to nab in a telescope, owing to dazzling nearby Sirius A. This feat will get easier as Sirius B approaches apastron with a max separation of 11.5 arc seconds in 2025.
Some paleoastronomers have also puzzled over ancient records referring to Sirius as “red” in color. While some have stated that this might overturn current astrophysical models, a far more likely explanation is its position low to the horizon for northern hemisphere observers. Many bright stars can take on a twinkling ruddy hue when seen low in the sky due to atmospheric distortion.
Let the Dog Days of Summer (& astronomy) begin! (Photo by author).
All great facts to ponder during these Dog Days of early August, perhaps as the sky brightens during the dawn and your vigil for the Perseid meteors draws to an end!
Echa un vistazo a esta ruta de punto a punto de 3,9-km cerca de 1º Distrito, Paris. Por lo general, se considera una ruta fácil, que se tarda una media de 53 min en recorrer. Esta ruta es excelente para el ciclismo en carretera, correr y pasear, y es poco probable encontrarse con otras personas mientras se recorre. La ruta está abierta todo el año y es perfecta para visitar en cualquier momento. Los perros son bienvenidos, pero deben permanecer atados con correa.
Este itinerario, que parte de la estación de metro de Louvre-Rivoli, recorre algunos de los principales lugares de interés del centro de París. El paseo discurre a orillas del Sena, frente al célebre Museo del Louvre. A la altura de la pasarela Léopold Sédar-Senghor, el recorrido atraviesa el Jardín de las Tullerías antes de llegar a la Madeleine y a la Ópera, para terminar en la estación de metro Richelieu-Drouot.
Eratóstenes era hijo de Aglaos. Estudió en Alejandría y durante algún tiempo en Atenas. Fue discípulo de Aristón de Quíos, de Lisanias de Cirene y del poeta Calímaco y también gran amigo de Arquímedes. En el año 236 a. C., Ptolomeo III le llamó para que se hiciera cargo de la Biblioteca de Alejandría, puesto que ocupó hasta el fin de sus días. La Suda afirma que, tras perder la vista, se dejó morir de hambre a la edad de 80 años; sin embargo, Luciano dice que llegó a la edad de 82 años; también Censorinosostiene que falleció cuando tenía 82 años.
A Eratóstenes se le atribuye la invención, hacia 255 a. C., de la esfera armilar que aún se empleaba en el siglo XVII. Aunque debió de usar este instrumento para diversas observaciones astronómicas, sólo queda constancia de la que le condujo a la determinación de la oblicuidad de la eclíptica. Determinó que el intervalo entre los trópicos (el doble de la oblicuidad de la eclíptica) equivalía a los 11/83 de la circunferencia terrestre completa, resultando para dicha oblicuidad 23º 51' 19", cifra que posteriormente adoptaría el astrónomo Claudio Ptolomeo.
Según algunos historiadores, Eratóstenes obtuvo un valor de 24º y el refinamiento del resultado se debió hasta 11/83 al propio Ptolomeo. Además, según Plutarco, de sus observaciones astronómicas durante los eclipses dedujo que la distancia al Sol era de 804 000 000 estadios, la distancia a la Luna 780 000 estadios y, según Macrobio, que el diámetro del Sol era 27 veces mayor que el de la Tierra. Realmente el diámetro del Sol es 109 veces el de la Tierra y la distancia a la Luna es casi tres veces la calculada por Eratóstenes, pero el cálculo de la distancia al Sol, admitiendo que el estadio empleado fuera de 185 metros, fue de 148 752 060 km, muy similar a la unidad astronómica actual. A pesar de que se le atribuye frecuentemente la obra Katasterismoi, que contiene la nomenclatura de 44 constelaciones y 675 estrellas, los críticos niegan que fuera escrita por él, por lo que se suele designar Pseudo-Eratóstenes a su autor.
En el solsticio de verano, los rayos solares inciden perpendicularmente sobre Siena (Asuán). En Alejandría, más al norte, midiendo la altura de un edificio y la longitud de la sombra que proyecta, se puede determinar el ángulo formado con el plano de la eclíptica, en el que se encuentran el Sol y la ciudad de Siena, ángulo que es precisamente la diferencia de latitud entre ambas ciudades. Conocida ésta, basta medir el arco de circunferencia y extrapolar el resultado a la circunferencia completa (360º).
Reconstrucción del siglo XIX (según Bunbury) del mapa de Eratóstenes del mundo conocido en su época.
Sin embargo, el principal motivo de su celebridad es sin duda la determinación del tamaño de la Tierra. Para ello inventó y empleó un método trigonométrico, además de las nociones de latitud y longitud, al parecer ya introducidas por Dicearco, por lo que bien merece el título de padre de la geodesia.
Por referencias obtenidas de un papiro de su biblioteca, sabía que en Siena (hoy Asuán, Egipto) el día del solsticio de verano los objetos verticales no proyectaban sombra alguna y la luz alumbraba el fondo de los pozos; esto significaba que la ciudad estaba situada justamente sobre la línea del trópico y su latitud era igual a la de la eclíptica que ya conocía. Eratóstenes, suponiendo que Siena y Alejandría tenían la misma longitud (realmente distan 3º) y que el Sol se encontraba tan alejado de la Tierra que sus rayos podían suponerse paralelos, midió la sombra en Alejandría el mismo día del solsticio de verano al mediodía, demostrando que el cenit de la ciudad distaba 1/50 parte de la circunferencia, es decir, 7º 12' del de Alejandría. Según Cleomedes, Eratóstenes se sirvió del scaphium o gnomon (un protocuadrante solar) para el cálculo de dicha cantidad.
Posteriormente, tomó la distancia estimada por las caravanas que comerciaban entre ambas ciudades, aunque bien pudo obtener el dato en la propia Biblioteca de Alejandría, fijándola en 5000 estadios, de donde dedujo que la circunferencia de la Tierra era de 250 000 estadios, resultado que posteriormente elevó hasta 252 000 estadios, de modo que a cada grado correspondieran 700 estadios. También se afirma que Eratóstenes, para calcular la distancia entre las dos ciudades, se valió de un regimiento de soldados que diera pasos de tamaño uniforme y los contara.
Admitiendo que Eratóstenes usase el estadio ático-italiano de 184.8 m, que era el que solía utilizarse por los griegos de Alejandría en aquella época, el error cometido sería de 6.192 kilómetros (un 15 %). Sin embargo, hay quien defiende que empleó el estadio egipcio (300 codos de 52,4 cm), en cuyo caso la circunferencia polar calculada hubiera sido de 39614 km, frente a los 40008 km considerados en la actualidad, es decir, un error de menos del 1%.
Ahora bien, es imposible que Eratóstenes diera con la medida exacta de la circunferencia de la Tierra debido a errores en los supuestos que calculó. Tuvo que haber tenido un margen de error considerable y por lo tanto no pudo haber usado el estadio egipcio:2
Supuso que la Tierra es perfectamente esférica, lo que no es cierto. Un grado de latitud no representa exactamente la misma distancia en todas las latitudes, sino que varía ligeramente de 110,57 km en el Ecuador hasta 111,7 km en los Polos. Por eso no podemos suponer que 7º entre Alejandría y Siena representen la misma distancia que 7º en cualquier otro lugar a lo largo de todo el meridiano.
Supuso que Siena y Alejandría se encontraban situadas sobre un mismo meridiano, lo cual no es así, ya que hay una diferencia de 3 grados de longitud entre ambas ciudades.
La distancia real entre Alejandría y Siena (hoy Asuán) no es de 924 km (5000 estadios ático-italiano de 184,8 m por estadio), sino de 843 km (distancia aérea y entre los centros de las dos ciudades), lo que representa una diferencia de 81 km.
Realmente Siena no está ubicada exactamente sobre el paralelo del trópico de cáncer (los puntos donde los rayos del sol caen verticalmente a la tierra en el solsticio de verano). Actualmente se encuentra situada a 72 km (desde el centro de la ciudad). Pero debido a que las variaciones del eje de la Tierra fluctúan entre 22,1 y 24,5º en un período de 41000 años, hace 2000 años se encontraba a 41 km.
La medida de la sombra que se proyectó sobre la vara de Eratóstenes hace 2.200 años debió ser de 7,5º o 1/48 parte de una circunferencia y no 7,2º o 1/50 parte. Puesto que en aquella época no existía el cálculo trigonométrico, para calcular el ángulo de la sombra, Eratóstenes pudo haberse valido de un compás,3 para medir directamente dicho ángulo, lo que no permite una medida tan precisa.
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The flooded Temple of Isis on the island of Philae circa 1905. (Credit: Wikimedia Commons under an Attribution-Share Alike 2.5 license. Author H.W. Dunning).
Sopdet as the personification of Sirius (note the star on the forehead) Wikimedia Commons image under an Attribution Share Alike 3.0 license. Author Jeff Dahl).
Sirius as the shining “nose” of the constellation Canis Major. (Created by the author using Starry Night).
The Colossi of Memnon Near Luxor, just one of the amazing architectural projects carried out by the ancient Egyptians. (Photo by author).
Sirius as seen via Hubble- can you spy Sirius B? (Credit: NASA/ESA Hubble image).
Let the Dog Days of Summer (& astronomy) begin! (Photo by author).
