The Sun

The Sun [1] is a giant fusion reactor busily engaged in the conversion of hydrogen (at present approximately 70% by mass) to helium (at present approximately 28%), a giver of life (electromagnetic radiation translates into heat and light, both being instrumental in photosynthesis) and the center of the Solar System. Its mass is approximately 99% of the Solar System's total, yet with a diameter of 1,390,000 kilometers, a core temperature of 15,000,000 Celsius and a surface temperature of 5,500 Celsius [2] it is by galactic standards fairly ordinary. [3]

Catagorized as a Population 1 (heavy element-rich) yellow dwarf, it's at four and a half billion years old almost halfway through its main sequence. Eventually, upon exhausting its hydrogen, it will expand into a red giant enveloping the inner planets before ejecting its outer layers and forming a planetary nebula. At the center of this glowing shell of ionized gas will be a tremendously hot stellar core, a remnant which will eventually cool and become a white dwarf. Ultimately its remaining heat having dissipated, all that will be left is a burned out ember, a black dwarf. [4]

[1] The Sun has been deified by many cultures throughout the course of human history: it was Helios the son of Hyperion and Theia to the Greeks, Sol to the Romans and Aten (or Aton) during ancient Egypt's 18th dynasty and the reign of Amenhotep IV (Akhenaten).

[2] The exception being sunspots, giant areas on the Sun's surface of reduced temperature (4,000 degrees Celsius). The visible manifestation of intense magnetic activity which inhibits heat transfer, they appear as dark blotches when compared to the surrounding photosphere.

[3] On February 11, 2010, NASA launched a revolutionary eight hundred milion dollar spacecraft into Earth orbit. The Solar Dynamics Observatory (SDO) will study our sun from a circular geosynchronous orbit, 22,300 miles (36,000 km) up, almost interruption free, for five years using three very high tech instruments: the Helioseismic and Magnetic Imager (HMI), the Atmospheric Imaging Assembly (AIA) and the Extreme Ultraviolet Variability Experiment (EVE). The main goal of the mission is to get a better understanding of how the Sun works, thereby allowing more accurate forcasting of space weather and the disruptive solar storms which can pose a threat to astronauts and play havoc with satellites, communications and electrical power grids.

[4] At present the Universe is believed to be too young for black dwarfs to exist.

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