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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 a list of auxiliaries of the United States Navy. It covers the various types of ships that support the frontline combat vessels of the United States Navy.
Auxiliary ships which function as hospital ships and as oilers are to be found in their own articles: List of United States Navy hospital ships and List of United States Navy oilers. Escort carriers, amphibious warfare vessels, and some mine warfare vessels were also originally classed as auxiliaries but were later given their own hull classification symbols outside the auxiliary series (which all begin with an 'A'). Links to these and other list articles of similar ships can be found throughout this article.
Yard and district craft also function as auxiliaries but generally are smaller and less capable than their ocean-going counterparts, and so they generally remain in harbors and coastal areas.
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