The Sun is an ordinary star, it is not to big or too small and it is not really old or young. It is the closest star to Earth, as well as the most closely studied. the Sun controls our climate and weather on Earth and is the source of heat that maintains life as we know it.
Some of the outer regions of the Sun's atmosphere that are observed and measured include:
The Photosphere:
The Sun essentially the same chemical elements as can be found on earth, except that the Sun is hot all the elements exist in the gaseous state. The Sun doesn't really have a "surface." Instead "think of it as a bunch of gas which gets denser as you move from space towards the solar core." The photosphere represents the depth at which we can longer see towards the core.
The Chromosphere:
The chromosphere is made up of the gases which extend away from the photosphere. The gases are transparent to most visible radiation.
The Corona:
The corona is the outermost region of the Sun;s atmosphere. The corona extends above the photosphere millions of miles into space. It usually can not be seen due to the brightness of the photosphere, but during a total solar eclipse, the corona shines against the dark sky.
More information about the sun can be found at:
http://imagine.gsfc.nasa.gov/docs/science/know_l1/sun.html
http://www.kidsastronomy.com/our_sun.htm
