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The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as light and infrared radiation. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (864,000 miles), or 109 times that of Earth, and its mass is about 330,000 times that of Earth. It accounts for about 99.86% of the total mass of the Solar System.
Roughly three quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron.The Sun is a G-type main-sequence star (G2V) based on its spectral class. As such, it is informally and not completely accurately referred to as a yellow dwarf (its light is closer to white than yellow). It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. It is thought that almost all stars form by this process.
Bergen | |
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State | Limburg |
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Population | 13098 |
Bergen (Norwegian pronunciation: [ˈbæ̀ɾɡn̩] (listen)), historically Bjørgvin, is a city and municipality in Vestland county on the west coast of Norway. At the end of 2019, the municipality's population was 283,929. Bergen is the second-largest city in Norway. The municipality covers 465 square kilometres (180 sq mi) and is on the peninsula of Bergenshalvøyen. The city centre and northern neighbourhoods are on Byfjorden, 'the city fjord', and the city is surrounded by mountains; Bergen is known as the 'city of seven mountains'. Many of the extra-municipal suburbs are on islands. Bergen is the administrative centre of Vestland county. The city consists of eight boroughs: Arna, Bergenhus, Fana, Fyllingsdalen, Laksevåg, Ytrebygda, Årstad, and Åsane.
Trading in Bergen may have started as early as the 1020s. According to tradition, the city was founded in 1070 by king Olav Kyrre and was named Bjørgvin, 'the green meadow among the mountains'. It served as Norway's capital in the 13th century, and from the end of the 13th century became a bureau city of the Hanseatic League. Until 1789, Bergen enjoyed exclusive rights to mediate trade between Northern Norway and abroad and it was the largest city in Norway until the 1830s when it was overtaken by the capital, Christiania (now known as Oslo). What remains of the quays, Bryggen, is a World Heritage Site. The city was hit by numerous fires over the years. The Bergen School of Meteorology was developed at the Geophysical Institute starting in 1917, the Norwegian School of Economics was founded in 1936, and the University of Bergen in 1946.