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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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York is a cathedral city and unitary authority area at the confluence of the rivers Ouse and Foss in England. The city is the county town of the historic county of Yorkshire. York is the most populous district within the lieutenancy area of North Yorkshire and second largest built-up area. City of York Council is a unitary authority responsible for providing all local services and facilities throughout the city and rural areas beyond the old city boundaries. The unitary authority is in the Leeds city region along with most of the former West Riding of Yorkshire, apart from South Yorkshire (in the Sheffield city region) and Derbyshire. At the 2011 census, the borough population was 198,051 and the population of the city was 153,717.
The city is known for its famous historical landmarks such as York Minster and the city walls, as well as a variety of cultural and sporting activities, which makes it a popular tourist destination in England. It is about 25 miles (40 km) north-east of Leeds and 34 miles (55 km) north-west of Kingston upon Hull.
The city was founded by the Romans as Eboracum in 71 AD. It became the capital of the Roman province of Britannia Inferior, and later of the kingdoms of Deira, Northumbria and Jórvík.
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