The Solar System is our little corner of the Milky Way: the Sun, eight planets, their moons, dwarf planets, asteroids, comets and a vast amount of smaller material left over from its formation about 4.6 billion years ago. It sounds reasonably tidy when reduced to a list like that, although in reality it is an enormous and rather complicated place.

At the centre of it all is the Sun, an otherwise fairly ordinary star which happens to be extremely important to us. Almost all of the mass of the entire Solar System is contained in the Sun. The planets, moons, asteroids and everything else account for only a small fraction of what remains. The Sun's gravity keeps this collection travelling around it, while its light and heat make life on Earth possible.

The four planets nearest the Sun — Mercury, Venus, Earth and Mars — are relatively small, rocky worlds. Although they are sometimes grouped together as the terrestrial planets, they are far from identical. Mercury is a heavily cratered world close to the Sun, Venus hides beneath a dense and extremely hot atmosphere, Earth has oceans of liquid water, and Mars is now a cold desert despite plenty of evidence that water once flowed across its surface.

Beyond Mars things become much larger. Jupiter is by far the largest planet and is followed by Saturn, famous of course for its spectacular system of rings. Further out are Uranus and Neptune, usually described as the ice giants. All four outer planets have substantial families of moons, and several of those moons are interesting worlds in their own right rather than simply lumps of rock going around a planet.

Between Mars and Jupiter lies the main asteroid belt. It is sometimes shown in films as an impossibly crowded obstacle course, but the real thing is nothing like that. The objects are spread across an enormous volume of space. A spacecraft passing through the asteroid belt is in considerably less danger of having to weave dramatically between rocks than Hollywood might suggest.

Beyond Neptune lies another great population of smaller bodies, including the Kuiper Belt. Pluto is one of these objects and has been classed as a dwarf planet since 2006. It may no longer appear in the official list of planets, but it remains one of the most familiar bodies in the outer Solar System and seemed far too interesting to leave off this page.

Comets generally spend much of their lives in the colder outer regions before occasionally travelling towards the Sun. As they warm, frozen material begins to escape and can produce the familiar glowing coma and tails. Some comets return regularly, while others may take thousands of years to complete a single journey around the Sun.

The distances involved become rather ridiculous surprisingly quickly. Earth is about 150 million kilometres from the Sun. This distance is known as one astronomical unit, or AU, and provides a rather more useful measuring stick once we start travelling around the Solar System. Jupiter is a little over 5 AU from the Sun, while Neptune is roughly 30 AU away.

Even Neptune is not really the edge. Beyond the known planets and the Kuiper Belt the Sun's influence continues much further into space. The distant Oort Cloud is thought to surround the Solar System and may be the source of many long-period comets. Exactly where the Solar System "ends" depends rather inconveniently on what you choose to mean by the Solar System.

Nor is everything simply arranged as a set of perfect circles on a flat sheet. The planets follow elliptical orbits, although most of them are fairly close to circular, and their orbital planes are slightly tilted relative to one another. Smaller bodies can have much stranger orbits: highly elongated, steeply inclined, or occasionally sharing complicated gravitational relationships with the planets.

The whole system itself is moving too. The Sun and everything travelling with it orbit the centre of the Milky Way, taking roughly a couple of hundred million years to make one circuit. So while we tend to picture the planets endlessly tracing the same paths around a stationary Sun, the entire arrangement is travelling through the Galaxy at the same time.

One of the awkward things about showing all this on a web page is scale. The planets are tiny compared with the distances between them. If the Sun and planets in the diagram above were drawn at their correct relative sizes and distances, most of the planets would be barely visible and there would be an impressive amount of completely empty screen.

The diagram above is therefore deliberately schematic rather than to scale. It is intended to show what is there and roughly where everything belongs, rather than reproduce several billion kilometres of space on your monitor. Doing that accurately would either require microscopic planets or a web page several million pixels wide. Neither seemed especially helpful.