- For alternative meanings see sun (disambiguation).
|Mean distance from Earth||150,000,000 km
|Visual brightness (V)||−26.8m|
|Relative diameter (dS/dE)||109|
|Surface area||6.09 × 1012 km²|
|Volume||1.41 × 1027 m³|
|Mass||1.9891 × 1030 kg|
|Relative mass to Earth||333,400|
|Relative density to Earth||0.26|
|Relative density to water||1.409|
|Surface gravity||274 m s-2|
|Relative surface gravity||27.9 g|
|Escape velocity||618 km/s|
|Surface temperature||5780 K|
|Temperature of corona||5 × 106 K|
|Luminosity (LS)||3.827 × 1026 J s-1|
|Period of rotation|
|At equator:||27d 6h 36m|
|At 30° latitude:||28d 4h 48m|
|At 60° latitude:||30d 19h 12m|
|At 75° latitude:||31d 19h 12m|
|Period of orbit around
|2.2 × 108 years|
The Sun (also called Sol) is the star in our solar system. The planet Earth and all of her sister planets, both the other terrestrial planets and the gas giants, orbit the Sun. Other bodies that orbit the Sun include asteroids, meteoroids, comets, Trans-Neptunian objects, and, of course, dust.
Table of contents
Physical and other characteristics
The Sun is a main sequence star, with a spectral class of G2, meaning that it is somewhat bigger and hotter than the average star but far smaller than a blue giant star. A G2 star has a main sequence lifetime of about 10 billion years, and the Sun is probably about 5 billion years old, as determined by nucleocosmochronology.
At the center of the Sun, where its density is 1.5 × 105 kg m-3, thermonuclear reactions (nuclear fusion) convert hydrogen into helium. 3.8 × 1038 protons (hydrogen nuclei) are converted to helium every second. This releases energy which escapes from the surface of the Sun in the form of electromagnetic radiation and neutrinos (and to a smaller extent as the kinetic and thermal energy of solar wind plasma and as the energy in the Sun's magnetic field). Physicists are able to replicate thermonuclear reactions with hydrogen bombs. Sustained nuclear fusion on Earth for electricity generation may be possible in the future, with nuclear fusion reactors.
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. The solar activity cycle includes old magnetic fields being stripped off the Sun's surface starting from one pole and ending at the other.
For some time it was thought that the number of neutrinos produced by the nuclear reaction in the Sun was only one third of the number predicted by theory, a result that was termed the solar neutrino problem. When it was recently found that neutrinos had mass, and could therefore transform into harder-to-detect varieties of neutrinos while en route from the Sun to Earth, measurement and theory were reconciled.
Observation of the Sun can reveal such phenomena as:
- Solar flares
- Solar prominences
- quiescent prominences
- eruptive prominences
- Coronal mass ejection
- Astronomical twilight
- Solar radiation
- Solar radius
- Solar energy
- Solar wind
- Timeline of solar astronomy
- Solar deity