by James Robinson

Created on: January 25, 2009

Our Sun is a star, and together with all the stars that we can see at night, it is part of an enormous assembly of stars called The Milky Way Galaxy. The word galaxy is the name used for very large numbers of stars that are part of the same related group. The Milky Way Galaxy is just one of many existing galaxies.

Compared to the Earth, the Sun is very large and very far away. It is a million times larger than the Earth and is 300,000 times heavier. Rotating on its axis, which is slightly tilted, the Earth travels an immense distance through space on an elliptical orbit around the Sun, taking one year, actually a little more than 365 days, to complete one orbit, moving at a speed of about 67,000 miles per hour at an average distance from the Sun of about 93 million miles. It is the combination of the orbital motion of the Earth and the tilt of its axis of rotation that results in the Earth's seasons.

There is land and sea, solid rock and water, on Earth, a world surrounded by an atmosphere of air, but on the Sun there are no rocks or water, no solids of any kind. The Sun is a huge ball of very hot gases, about 72% hydrogen and 27 % helium, and the remaining 1% is made up of many of the same materials that exist on earth, called elements, but on the Sun in a gaseous state. The visible outer layer of the Sun, called the photosphere, is composed mainly of hydrogen at a temperature of about 5,500 degrees Celsius. Deep in the interior at the core, which we cannot see, the temperature is calculated to be fifteen million degrees Celsius or more and the pressure there is 300 billion times that of the atmosphere at the surface of the Earth with a density of about 12 times that of solid lead on Earth. It is this extreme heat and pressure at the core that enables and maintains the nuclear fusion processes that generate the Sun's heat and light. In simple terms, it does so by converting hydrogen to helium in a very complex multi-step fusion process that also releases immense amounts of energy that slowly makes its way from the core to the surface and streams out of the sun in all directions in the form of heat and light and other radiation. Just a small portion of that total output reaches earth while the rest streams out into space. This radiation is called the Solar Wind.

In the continuous fusion process, about four million tons of the Sun's mass is converted into energy every second. Even at this prodigious rate, the Sun should continue to exist for another four and a

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