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The sun is the solitary star of our solar system, sometimes called Sol. The planet Earth and all of her sister planets, both the other terrestrial planets and the gas giants, orbit the sun in accordance with Newton's Laws of Gravity.
The sun is the nearest star to Earth and the brightest object in the sky.
Other bodies that orbit the sun include asteroids, meteoroids, comets, Trans-Neptunian objects, and, of course, dust.
The sun is a main sequence star, with spectral class G2, meaning that it is somewhat bigger and hotter than the average star but far smaller than the largest red giant star. A G2 star has a main sequence lifetime of about 10 billion years, and the sun has probably about 5 billion, as determined by nucleocosmochronology. One outstanding question about the sun is the difference between the number of neutrinos observed from the sun, and the number predicted by theory, the solar neutrino problem.
Other characteristics of the sun are:
| Diameter | 1,392,000 km |
|---|---|
| Surface area | 6.09 × 1012 km2 |
| Volume | 1.41 × 1027 m3 |
| Mass | 1.9891 × 1030 kg |
| Relative mass | 333,400 Earth masses |
| Density | 1411 kg m-3 |
| Central density | 1.5 × 105 kg m-3 |
| Surface gravity | 274 m s-2 |
| Surface temperature | 5780 K |
| Period of rotation | |
| At equator: | 27 d 06 h 36 m |
| At 30° latitude: | 28 d 04 h 48 m |
| At 60° latitude: | 30 d 19 h 12 m |
| At 75° latitude: | 31 d 19 h 12 m |
| Mean distance from Earth | 150,000,000 km |
| Apparent magnitude | -27 |
| Absolute magnitude | 4.8 |
The composition of the sun's photosphere is 73.46% hydrogen, 24.85% helium, 0.77% oxygen, 0.29% carbon, 0.16% iron, 0.12% neon, 0.09% nitrogen, 0.07% silicon, 0.05% magnesium, and 0.04% sulphur. All matter in the sun is in the form of plasma due to its extreme temperature. This makes it possible for the sun to rotate faster at its equator than it does at higher latitudes, since the sun is not a solid body. The differential rotation of the sun's latitudes causes its magnetic field lines to become twisted together over time, causing magnetic field loops to erupt from the sun's surface and trigger the formation of the sun's dramatic sunspots and solar prominences.
Observation of the sun discloses such phenomena as : (Caution: direct observation of the sun can cause permament sight loss.)
- Sunspots
- faculae
- Solar flares
- Solar prominences
- quiescent prominences
- eruptive prominences
Other terms related to the sun :
See also: sun mythology
Solar system:
Sun - Mercury - Venus - Earth - Mars - Asteroids - Jupiter - Saturn - Uranus - Neptune - Pluto - Comets