Our Solar System

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What is a solar system? 'Solar' refers to the Sun our host star. However, we use the phrase 'Solar system' for all kinds of star-systems, not just our own. Our system consists of a star (Sun) and a number of planets. History The ancient greeks had a (for it's time) decent model of our solar system although not a correct one. Ptolemaos was the philosopher who developed the famous Geocentric model with everything orbiting Earth in perfect circular orbits. (Geocentric means the Earth was thought to be the center of the Universe as opposed to the Heliocentric model where the Sun is placed at the center.) Another philosopher at the time (~260BC)presented a Heliocentric model. His name was Aristarchus and as good as his idea was, he could not find a way to prove it. Not much happened until the early 1540's when Nikolai Copernicus presented the revised Heliocentric model. He is generally recognized as the father of the Heliocentric model, although others may beg to differ. The 1540's though wasn't a very good time for scientist to propose theories that contradicted those of the Church at the time (Geocentric view). It would take some more effort by Tycho Brahe and later Johannes Kepler to scientifically prove that the Geocentric model was inaccurate. Kepler also realized that the planetary orbits weren't perfect circles at all, but rather elliptical. The work of Galileo Galilei and perhaps most importantly, Isaac Newton finally brought an accurate model of the Solar system and with the mathematics to prove it.          Later of course, the model was refined once more when Albert Einstein's theory of relativity was presented. But in fact, for most simpler calculations, Kepler's laws of planetary motion are still in use to this day. Since the beginning of the last century, we have a very accurate model of our Solar system, but for a long time, we had no idea if our system is one of a kind or if there are lot's of systems like ours out there. There were those who thought that our type of system is very common and others who thought that it's not even certain other stars than our Sun have planets at all. (Stupid, yes) For the past couple of years, our methods for observing other stars have become better and these days we can actually detect planets around other stars. As you read this, more than 100 planets have been found outside our own solar system. (Take a look here.) That may sound a lot, but we need to remember that our observational technique is in it's infancy. So far, we've only detected those that were easy to spot (the big planets). In about 10-15 years we will have new tools at our disposal and the number of detected planets will then likely grow extensively. The members Our solar system consists of numerous objects, no one knows exactly how many, simply because we have not yet examined the outer regions of the system and we do not have the technology to detect objects below a certain size. What we do know, is the number of planets and large moons. Our Sun is orbited by at least 9 planets and a bunch of smaller objects (Planetoids, Asteroids, comets etc). Many of these planets have their own moons. As you know of course, the Earth has only one moon, but the much larger Jupiter has over 60 moons. Let's take a look at the larger members in the solar system. As I mentioned on the previous page, it is impossible to show the true size and distance relationships between planets. Below is a picture showing the Sun and the planets with approximate size relations, but the relative distances are of course completely inaccurate.

The outer limits

Moving on...