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The Sun (☉) is benign and favourable, and presides over the head according to Marcus Manilius (1st century EV) in his epic (8000 verses) poem Astronomica. It is usually thought to represent the conscious ego, the self, and the principles of creativity, spontaneousness, health and vitality - the life force. The Sun is the planetary ruler of Leo.
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Symbolism and Astrology
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The Sun (also called Sol) is the star in our solar system. Planet Earth orbits the Sun. Other bodies that orbit the Sun include other planets, asteroids, meteoroids, comets and dust. Not all objects passing through the solar system have been orbitally captured by the Sun's gravity, but these exceptions are few and their masses are small. More generally the primary stellar body around which an object orbits is colloquially called its "sun", and stars in a multiple star system are referred to as the "suns" of bodies in that system.
Physical and other characteristics
The Sun is a main sequence star, with a spectral class of G2, meaning that it is somewhat more massive and hotter than the average star but far smaller than a blue giant star. A G2 star is on the main sequence, and has a lifetime of about 10 billion years, and the Sun formed about 5 billion years ago, as determined. The Sun orbits the Milky Way galaxy at a distance of about 25,000 to 28,000 light-years from the galactic center, completing one revolution in about 226 million years. The orbital speed is 217 km/s, i.e. 1 light-year in ca. 1400 years, and 1 AU in 8 days.
The Sun is a near-perfect sphere, with an oblateness estimated at about 9 millionths (mostly due to the gravitation of Jupiter), which means the polar diameter differs from the equatorial by 10 km at most. This is partly because the centrifugal effect of the Sun's rather sedate rotation is 18 million times weaker than its surface gravity (at the equator).
Perhaps counterintuitively, the Sun does not have definite boundaries as rocky planets do. Instead, the density of gases comprising the Sun drops off following an exponential relationship with distance from the center of the Sun. The Sun's radius is measured from center to the edges of the photosphere.
At the center of the Sun, where its density is 1.5×105 kg/m3, thermonuclear reactions (nuclear fusion) convert hydrogen into helium. About 8.9×1037 protons (hydrogen nuclei) are converted to helions (helium nuclei) every second. This releases energy at the matter-energy conversion rate of 4.26 million tons per second (about 9.1×1016 tons of TNT per second) 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). A fusion reactor, which some physicists believe may one day provide power for human use, would use a similar process to extract atomic energy.
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. 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.
The corona has a density of 1011 particles/m3, and the photosphere a density of 1023 particles/m3.
For some time it was thought that the number of neutrinos produced by the nuclear reactions in the Sun was only one third of the number predicted by theory, a result that was termed the solar neutrino problem. Several neutrino observatories were created including the Sudbury Neutrino Observatory to try and measure the amount of neutrinos given off by the Sun. From these observatories and experiments it was recently found that neutrinos had rest mass, and could therefore transform into harder-to-detect varieties of neutrinos while en route from the Sun to Earth; thus measurement and theory were reconciled.
To obtain an uninterrupted view of the Sun, the European Space Agency and NASA cooperatively launched the Solar and Heliospheric Observatory (SOHO) on December 2, 1995.
Observation of the Sun can reveal such phenomena as:
- Sunspots – A comparatively “dark” region on the Sun's surface (photosphere) that is marked by a lower temperature than its surroundings, and intense magnetic activity.
- Faculae - Bright spots that form in the canyons between solar granules.
- Granules - Continent-sized areas that are the tops of convection cells.
- Solar flares - Violent eruptions that explode from a star's photosphere
- Solar prominences - A structure in the corona consisting of cool plasma supported by magnetic fields.
- Coronal mass ejection - A solar event which emits a burst of plasma
Caution: looking directly at the Sun can damage the retina and one's eyesight.
The astronomical symbol for the Sun is a circle with a point at its center.
The composition of the Sun is not known with any great precision. A solar wind sample return mission, Genesis (spacecraft), returned to Earth in 2004 and is undergoing analysis, but it was damaged by crash-landing when its parachute failed to deploy on reentry to Earth's atmosphere.
The Death of Sol
Our sun does not have the mass to Nova or Supernova. However in 4-5 billion years it will enter its red giant phase, expanding as the hydrogen fuel in the core is consumed and it starts to burn heavier elements that are present. While it is likely that this expansion will reach the current position of Earth's orbit, recent research suggests that mass loss from the Sun earlier in its red giant phase will cause the Earth's orbit to move further out, preventing it from being swallowed. Following the red giant phase, the Sun will become a white dwarf, slowly cooling for a further 5 billion years or so.
- Wikipedia (2005). Planets in Astrology (http://en.wikipedia.org/wiki/Planets_in_astrology). Retrieved March 2, 2005
- Wikipedia (2004). Sun (http://en.wikipedia.org/wiki/Sun). Retrieved Nov. 30, 2004.
- Wikipedia (2004). Sunspot (http://en.wikipedia.org/wiki/Sunspot). Retrieved Nov. 30, 2004.
- Wikipedia (2004). Facula (http://en.wikipedia.org/wiki/Facula). Retrieved Nov. 30, 2004.
- Wikipedia (2004). Solar flare (http://en.wikipedia.org/wiki/Solar_flare). Retrieved Nov. 30, 2004.
- Wikipedia (2004). Spicule (solar physics) (http://en.wikipedia.org/wiki/Spicule_%28solar_physics%29). Retrieved Nov. 30, 2004.
- Wikipedia (2004). Coronal mass ejection (http://en.wikipedia.org/wiki/Coronal_mass_ejection). Retrieved Nov. 30, 2004.
- NASA (2004). SOHO FAQ (http://sohowww.nascom.nasa.gov/explore/faq/sun.html). Retrieved Nov. 30, 2004.
- Current SOHO snapshots (http://sohowww.nascom.nasa.gov/data/realtime-images.html)
- Far-Side Helioseismic Holography (http://soi.stanford.edu/data/farside/index.html) from Stanford (http://www.stanford.edu)
- NASA Eclipse homepage (http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html)
- Nasa SOHO (Solar & Heliospheric Observatory) satellite (http://sohowww.nascom.nasa.gov/)FAQ (http://sohowww.nascom.nasa.gov/explore/faq/sun.html)
- Solar Sounds (http://soi.stanford.edu/results/sounds.html) from Stanford (http://www.stanford.edu)
- Spaceweather.com (http://www.spaceweather.com)