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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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This is the outline of the geography of the city of Ottawa, the capital of Canada. Ottawa's current borders were formed in 2001, when the former city of Ottawa amalgamated with the ten other municipalities within the former Regional Municipality of Ottawa–Carleton. Ottawa is now a single-tiered census division, home to 870,250 people.
The city centre is located at the confluence of the Ottawa and Rideau Rivers. The Ottawa River forms the entire northern boundary of the city which it shares with the province of Quebec's municipalities of Pontiac and Gatineau. The northern boundary begins in the west at Arnprior and continues east to Rockland. The boundary then turns south in a straight line, separating the former Township of Cumberland (now in Ottawa) and the City of Clarence-Rockland. It then turns west in another straight line separating the former Township of Cumberland with the municipalities of The Nation and Russell.