The solar system, our place in the universe

Our solar system is a system of planets, moons, asteroids, meteors and comets that are held together by the suns gravitational force. The solar system ends at the point where objects are no longer affected by the suns gravitational field, solar winds have no influence and the suns vast magnetosphere ends. The planets and other objects revolve in an elliptical orbit around the sun, which is the center of our solar system.

The sun

The sun is our very own star; a giant gas sphere that converts Hydrogen into Helium and in the process emits warmth and light. The sun is quite ordinary and unremarkable among the billions of other stars out there. The sun is estimated to be five billion years old and is thought to last another five billion years. The surface temperature of the sun is estimated to be somewhere between five and six thousand degrees Celsius while the core temperature is around fifteen million degrees!

The inner planets

The first four planets from the sun are Mercury, Venus, Earth and Mars. These are called the inner planets or 'terrestrial planets' after the Latin word terra which means land. They have a dense, metallic core and a solid, rocky surface. Mercury is relatively small; its diameter is about a third of the Earths diameter. At a distance of fifty-eight million kilometers Mercury orbits the sun in eighty-eight days. It's a planet of extremes, during the day the temperature can soar to a blistering 400 degrees Celsius while the nights are freezing cold at minus 200! Venus is about the same size as Earth and is a little further from the sun than Mercury resulting in the fact that it takes 225 earth days to circle the sun. With the naked eye we can observe Venus as a very bright star. Because Venus is closer to the sun it will rise above the horizon 2 hours before sunrise or disappear behind the horizon two hours before sunset, depending on its position in its orbit around the sun. Venus is therefore also called the Morningstar or Evening star. Our own Earth is 150 million kilometers from the sun; this is also referred to as one astronomical unit (AU). The last of the inner planets is Mars, at 1.52 astronomical units. Mars has two moons, Phobos and Deimos, and takes 687 days to complete its orbit around the sun. Mars gets its red color from the abundance of iron ore contained in its surface that has been oxidized by a small amount of oxygen.

The outer planets

The four outer planets are Jupiter, Saturn, Uranus and Neptune. These are also known as the gas giants and consist of large gas spheres with a relatively small rocky core. Jupiter is the largest of the planets in our solar system and it has twice as much mass as all other planets combined. Jupiter is 5.2 astronomical units removed from the sun and it takes 11.9 Earth years to complete one orbit around the sun. Jupiter has sixty-three known moons, most renowned among these are the four Galilean Moons. These owe their name to their discovery by Galileo Galilei in 1610. Saturn is the planet surrounded by beautiful rings. These rings consist of rubble and debris that is in orbit around the planet.  It probably comes from a moon that was destroyed. Saturn has forty-eight known moons and this planet at 9.54 astronomical units takes 29.5 years to travel around the sun. Uranus is the only planet that is on its side, because the axis around which the planet revolves is at a ninety-eight degrees angle to its orbital plane. Uranus has twenty-seven known moons. The last planet in our solar system is Neptune which is no less than thirty times further from the sun than our Earth. The result of this enormous distance to the sun is that it takes Neptune 165 years to complete its orbit around the sun. There are currently thirteen known moons of Neptune.

Other objects in our solar system

Between the orbits of Mars and Jupiter lies the asteroid belt, a ring of asteroids. Asteroids are nothing more than giant rocky objects circling the sun. It is thought that they are the remains of a planet that could not be fully formed because of the disruptive force of Jupiter's gravity. Outside Neptune's orbit there is a second asteroid belt, it's called the Kuiper Belt after the Dutch astronomer Gerard Kuiper. Nowadays Pluto, formerly known as the furthest planet from the sun, is considered a part of the Kuiper Belt and therefore just a dwarf planet. Outside these two belts other rocky objects occur in the form of asteroids and meteoroids. The difference between these two is strictly the size, everything with a diameter of less than 50 meters is considered to be a meteoroid. When such a meteoroid enters Earth's atmosphere it will usually burn up and is then called a meteor. This phenomenon is commonly known as a falling star. When a meteoroid is of sufficient size a piece can reach the Earth's surface and this is called a meteorite. The last objects in our solar system are comets. A comet is in essence no more than a dirty ball of snow and ice with a rocky core. Comets have a strongly elliptical orbit around the sun which means they are out of our sight for quite long periods of time. When they travel close enough to the sun the ice instantly turns to gas, which makes up a comets tail.

Sources: www.todio.nl