Sun

The Sun is one of more than 100 billion stars in our galaxy. It is classified as being in the 10% by mass. The Sun is a big ball of reacting gases and presently it is composed of 75% hydrogen and 25% helium. The Sun does not burn in the same way as a fire does, intense pressure and heat cause the hydrogen and helium atoms to come together in a scientific process called fusion. When this occurs a type of energy called nuclear energy is produced. The heat on the surface of the Sun is estimated to be a whopping 6000 C. The Sun shows some awesome features and should not only be thought of as providing light and heat. Sunspots, one of these features are dark spots on the Sun's surface and are formed by the cooler areas on the Sun's surface. Another of these features are solar flares. They can be seen as spectacular arcs of flames being emitted from the Sun's surface.
The Sun has been around for approximately 4.5 billion years and is expected to have enough fuel to be around for another 5 billion, so nothing for us alive to worry about.

Mercury

Mercury is the eighth largest planet and the closest to the Sun. It takes 89 earth days to complete one revolution (that is a day on Mercury lasts 89 earth days). Mercury's surface is scarred with many craters probably due to many meteoroids attacks during the early years of the solar system. It has a very thin atmosphere and this is constantly replenished by solar winds. Temperatures on the surface range from 427 to -170 C.

One of the largest features on Mercury's surface is the Caloris Basin it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Like the lunar basins, it was probably caused by a very large impact early in the history of the solar system. That impact was probably also responsible for the odd terrain on the exact opposite side of the planet.

Surprisingly observations of the North Pole show evidence of water ice in the protected shadows of some craters.

Venus

Venus is the sixth largest planet and the second closest to the Sun. It takes 243 Earth days to complete one full rotation, and only 225 Earth days to complete one revolution around the Sun. This makes Venus unique in that a year on the planet lasts longer than a day. Another unique fact about Venus is that it is the only planet in the solar system, which rotates clockwise. Venus's atmosphere is extremely thick, approximately 90 times thicker than that of earths and is compromised mainly of carbon dioxide. This, along with active volcanoes and sulphuric acid has created a runaway greenhouse effect, which cause temperatures on Venus to rise up to 482 C. It is believed that oceans at one time existed, but the extreme hot climate and greenhouse effect would have evaporated them.

The majority of Venus's surface is covered with gently rolling planes. Unlike Mercury, Venus shows very little scars from meteoroid attacks. This is likely the case because meteoroids would have burned up in the very dense atmosphere. Where there is evidence of craters these appear in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere.

Earth

Earth is the third planet from the Sun and the fifth largest. As seen from satellite images it is a beautiful, bright blue planet filled with patches of white water vapour (clouds) that cover about 40% of the earth.
Unlike all other planets, earth actually supports life. Well, it is uncertain whether any of the planets in this solar system has living organisms or used to have.

Scientists believe that earth was formed 4.5 billion years ago when many other planets formed. The earth takes 365 days (1 year) to orbit the Sun and completes one rotation in 24 hours (a day). It is known that the tilt of the earth's axis is 23.5 degrees, which accounts for the seasons on earth. The tilt causes certain parts of the planet to be heated differently thus causing seasonal changes.

Of all the inner planets (Mercury, Venus, Earth, and Mars), Earth is the only one that contains water in its liquid form. This is essential to the development of life on Earth, as scientists believe. Since water was so important for life on earth, scientists today use liquid water as one of the key factors when searching for life on other planets inside and out of our solar system.

Earth has an atmosphere made up of nitrogen, carbon dioxide, hydrogen, oxygen and water vapour. One of the more important layers in the atmosphere is the ozone layer. This layer helps to protect earth from dangerous radiation and reflects most of the radiation from entering earth. The ozone layer is approximately 10 miles up from the ground.

The surface of the earth is covered by land and water. Approximately 72% of the earth's surface is covered by water, the greatest concentration of this being found in the oceans. The remaining 28% forms the landmasses. The land is shaped with many mountains, hills and valleys. The highest sets of peaks are the Himalayan Mountains, with the tallest Mount Everest reaching some 29,035 feet into the air. Although Everest is the tallest peak starting from the land surface, the highest mountain can actually be found on the island of Hawaii. Mauna Kea stretches 13,796 feet above water and 19,680 feet underwater, for a total of 33,476 feet!