The sun, a star, is a mass of incandescent gas (hydrogen, helium, etc.) that is sustained by a process called �fusion.� It is at the center of our solar system and is one of the gravitational foci that our solar system�s planets revolve around. The Sun itself orbits the center of the Milky Way galaxy. �Fusion� converts hydrogen, the fuel of the sun, into helium. Eventually, the sun will run out of fuel and eventually burn out. It has burned through approximately half of the fuel it had when it was created 4.57 billion years ago.

Mercury is the closest planet to the Sun; it orbits around the Sun every 88 days. Because of its size and close proximity to the Sun, it has no satellites to speak of. It also has a negligible atmosphere. When Pluto is not considered in the solar model, Mercury is the smallest planet in our solar system; two of Jupiter�s moons (Ganymede and Titan) are larger than it! The surface of Mercury is very similar to that of the Moon due to the lack of a substantial atmosphere.

Venus is the second closest planet to the Sun; it orbits around the Sun every 224.7 days. Against common sense, it is actually hotter than Mercury because it has an atmosphere conducive to the greenhouse effect. Due to its similarity in size, Venus is sometimes called Earth�s �sister planet�. Some scientists believe that the Earth will end up like Venus if Earth�s global warming problem is not handled. Venus, like Mercury, has no moons.

Earth is the planet we all inhabit. It is the only portion of space in the known universe that provably has intelligent life (or any kind of life for that matter). Earth happens to also be the only planet known to have liquid water. Earth is approximately as old as the Sun, 4.57 billion years old, and revolves around the sun every 365.26 days. Most Americans would think that the Earth is warmer when it is closer to the Sun. This is incorrect, it is actually colder; they would not take into account that the Earth rotates at an angle. The Earth has one moon, the Moon.

Mars is the fourth planet from the Sun; its name comes from the Roman god of war. It is often referred to as the �Red Planet� due to its iron (III) oxide laden surface. Mars has two small, misshapen moons. If one were to put Mars and the Earth next to each other, they would see a small difference in size or surface area. However, if one were to stick them on a huge weight scale, one would see that the Earth is ten times more massive. Why? Because Earth is composed of much more dense material than Mars.

Jupiter is the fifth planet from the Sun, it takes nearly 12 years to revolve around the Sun. It is the largest planet in our solar system and over twice as massive as the rest of the planets combined. It receives its name from the Roman God (who happens to be the �king� of the gods). It is the closest gas giant to the Earth. Similar to the Sun, it is comprised of mostly hydrogen and helium. It has been explored by Pioneer, Voyager, and Galileo. It is famous for having the �Great Red Spot�, a storm that is over 150 years old, estimates as to its true age go as far back as 340 years. It was first seen by Cassini. It has at least 63 moons and four particularly large moons (also known as the Galilean Moons).

Saturn is the sixth planet from the Sun. It is the second largest planet after Jupiter. It takes Saturn 29.5 years to make a revolution around the Sun. Saturn is well known for having its rings. The rings are mainly comprised of ice with some dust. Saturn has at least 57 moons. Its largest moon is Titan and is larger than Mercury. Titan is the only moon that poses an atmosphere. Titan also has volcanoes, the source of its atmospheric methane. Titan�s dense atmosphere has made it very difficult to observe.

Uranus is the seventh planet from the Sun, it takes 84 years for Uranus to revolve around the Sun. It is the first planet to be discovered in relatively modern astronomy (1780s). Uranus is composed of different kinds of gas and ice. Its atmosphere is 83 percent hydrogen, 15 percent helium, 2 percent methane with some traces of acetylene. Uranus� cyan color is an effect of the atmospheric methane. Uranus is also very cold; its surface temperature is -360 degrees Fahrenheit. Uranus has 27 moons.

Neptune is the eight planet from the Sun, it takes 165 years for Neptune to revolve around the sun. Neptune is the first planet to ever be discovered mathematically instead of empirically. This was done by noticing irregularities in the orbit of Uranus. Neptune has three large moons and five minor moons. Neptune has the strongest winds of any planet. It is also one of the coldest planets at � 360 degrees Fahrenheit. It has only had one visitor, Voyager 2 in 1989.

Recently, Pluto has been disregarded as a planet. Previously, it was the ninth planet from the Sun, it has three satellites. It would have been the smallest planet in our solar system. It was first discovered in 1930 by Clyed Tombaugh. In 2006, Pluto was removed by the International Astronomical Union as being a planet in its new definition of a planet.