The Solar System
Our Solar System
The solar system includes everything that orbits our sun. As well as the 8 planets, there are asteroids, comets and, dwarf planets. The image below shows planets in their order from the sun. This is not to scale but the relative sizes of each planet is accurate if you double the gas giants diameters.
The first four planets are known as terrestrial planets. They have common characteristics such as they are all rocky and do not have rings. The last four planets are known as gas giants these planets are all very large and have rings.
Also in the solar system is the asteroid belt this is an area between Mars and Jupiter that contains many thousands of asteroids. Asteroids are large pieces of rock, ice and metal that altogether are estimated to be 4% the weight of our moon.
Also floating around the solar system are Dwarf Planets. This is a new classification that was introduced in 2006. There are 3 dwarf planets in our solar system. One (Ceres) is in the asteroid belt. Then there is Pluto, which was a planet for almost 80 years before being reclassified, and finally Eris, which is even further out of the solar system than Pluto is.
As you will undoubtedly know, gravitational pull is a force that means apples fall to the ground and don't float and that we can stand. However, earth is not the only planet that has gravity. In fact, everything in the universe has a degree of gravity pulling things towards it. So why don't we bump in to each other?
Well ... the amount of gravity something has depends upon its mass. Therefore, the earth (which is pretty large) exerts an enormous amount more gravity than an individual person. And therefore, the moon, which is smaller than the earth, has a smaller gravity. On the other hand, the biggest planet in the solar system (Jupiter) has a mass 11 times that of Earth, and so its gravitational pull is 11 times greater. This means any human would be crushed if we were on the planet.
A comet consists of dust, ice and carbon dioxide. They also orbit the sun but the orbit is very eliptical. The diagram below outlines how the comet orbits the sun.
Put your finger on the screen over the diagram, trace the comet's path by speeding up towards the sun, until it is catapaulted away. It then slows down until almost stopping at the right, then the orbit turns and the comet speeds up as it approaches the sun.
Following this orbit you will see that the comet will spend the majority of its time outside of the solar system, and it is for this reason that astronomers are so interested in comets: because they only can be seen periodically. The most visible and therefore famous comet is Comet Halley and appears in the solar system every 75 years. It has been mentioned in historical texts for the last 3000 years.
An important feature of the comet is the tail, this is dust and gas produced by the heating from the sun. Therefore the tail is always opposite the side that is facing the sun.
Updated: 09 May 2012