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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.
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Tamanrasset (; Arabic: تامنراست), also known as Tamanghasset or Tamenghest, is an oasis city and capital of Tamanrasset Province in southern Algeria, in the Ahaggar Mountains. It is the chief city of the Algerian Tuareg. It is located an altitude of 1,320 metres (4,330 ft). As of the 2008 census, it has a population of 92,635, up from 72,741 in 1998, with an annual growth rate of 2.5%.Tamanrasset was originally established as a military outpost to guard the trans-Saharan trade routes. Surrounded by the barren Sahara Desert, very high temperatures of over 47 °C (117 °F) have been recorded here.
Vidin (Bulgarian: Видин, pronounced [ˈvidin]) is a port town on the southern bank of the Danube...
Teresina is the capital and most populous municipality in the Brazilian state of Piauí. Being...
Salzburg (Austrian German: [ˈsaltsbʊɐk]; German: [ˈzaltsbʊɐk] (listen); literally "Salt...