What we know as the sun is actually a star that is part of this solar system and part of the 100 million stars in the Milky Way Galaxy. The sun is a class G2 star. What that means is that the sun is average. This star is also only 4.5 billion years old and is only half way through its life cycle of 10 billion years. That means, in about 5 billion years, the sun would grow to such an enormous extent that it would even engulf Earth!

The Sun is also the source of energy (as in light and heat) for Earth. Not only is the sun important for Earth's survival, it has been used as a reference point for astronomers since ancient people first observed the sun. Today, we classify distances in space according to the distance between the sun and the earth, which is one AU (Astronomical Unit). One AU is equal to 93 million miles or 150 million kilometers. So that means the sun is 93 million miles away from Earth.

Another classification of distance is the Light Year. It is the distance that light travels is one year at the speed of 300,000 km/s or 186,000 miles per second. In one year, at that speed, light travels approximately 6 million miles. To understand the extent of space, you have to realize how many light years it takes just to travel through the Milky Way Galaxy alone. It takes more than 100,000 light years to travel through the Milky Way Galaxy, where we are located, and that's just one Galaxy. The Universe has an untold number of Galaxies revolving in space. Now imagine how small one AU is. Light travels one AU in only 8 minutes! So earth is just an invisible dot in the universe!

To understand the sun, we have to know its characteristics and composition. It is known that the sun generates energy through fusion of its hydrogen atoms that make up the sun. How do we know that the sun is made of Hydrogen, a gas that is found on earth also? Every element has a distinct spectrum and on earth we know the spectrum of Hydrogen so through observations of the sun though a spectrograph, we could conclude that the sun is made of Hydrogen.

The Sun is made up of Hydrogen atoms that through the process of fusion, releases a huge amount of energy. The sun contains 99.9 percent of the mass in this solar system. The reason the sun undergoes fusion of its hydrogen atoms is the immense force of gravity from the dense mass of the hydrogen atoms. The hydrogen atoms are forced to combine and form helium atoms while releasing a great amount of energy (Essentially the definition for the process of fusion).

The sun, even though we could not see this with our naked eyes, has an extremely turbulent atmosphere. There are solar flares, which are sudden eruptions of enormous energy in certain regions of the sun. Common observances are sunspots. These sunspots appear for a small amount of time, usually several weeks and are just dark spots on the sun. They appear because the spots are cooler than the rest of the sun. The reason certain spots on the sun become cooler is that the sun's magnetic field and the convective forces sometimes changes the amount of energy released at certain locations on the sun.