The Sun (Sol)

The Sun is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest). It is often said that the Sun is an "ordinary" star. That's true in the sense that there are many others similar to it.

Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy. Its diameter is 1,390,000 km, with a surface temperature of 5800 Kelvinand core temperatire of degrees 15,600,000 K. The Sun is personified in many mythologies: the Greeks called it Helios and the Romans called it Sol.
The Sun is, at present, about 70% hydrogen and 28% helium by mass everything else ("metals") amounts to less than 2%. This changes slowly over time as the Sun converts hydrogen to helium in its core.

The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf -- the final end product of a star like ours. It may take a trillion years to cool off completely.

The outer layers of the Sun exhibit differential rotation: at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. Similar effects are seen in the gas planets.

Observations over many years reveal a remarkable feature of the Sun: the number of sunspots varies in a periodic manner, usually described as the 11 year cycle (in actuality, the period varies, and has been closer to 10.5 years this century). The 11 year sunspot cycle is related to a 22 year cycle for the reversal of the Sun's magnetic field.

Although the number of sunspots is the most easily observed feature, all aspects of the Sun and solar activity are influenced by the solar cycle, such as coronal mass ejectionsand geomagnetic activity.

To view the sun today click here