Our planet Earth is one of eight that orbit our nearest star, the Sun. The planets that orbit our Sun are, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. There are also three dwarf planets that orbit our Sun and they are, Ceres, Pluto and Eris.

Below is an image of the the Sun and its four rocky planets, Mercury, Venus, Earth and Mars, in what is known as the inner orbit.



The next image shows both the rocky inner orbit planets and the gas planets of the outer orbit, Jupiter, Saturn, Uranus and Neptune (not forgetting the dwarf planet Pluto that comprises mainly of rock and ice).



The gas planets of the outer orbit have solid cores and gaseous exteriors as shown in the image below.



Just as we have our Moon that orbits the Earth, so do many of the other planets. Below is a list of each planet, plus the dwarf planet Pluto, and how many moons each one has orbiting it.

Mercury 0
Venus 0
Earth 1
Mars 2
Jupiter 62
Saturn 33
Uranus 27
Neptune 13
Pluto 1

Not all the moons are inactive like our own, some have atmospheres, volcanic activity, surface liquids and even water (more likely to be ice than in liquid form). In fact, we are more likely to find life on one of the solar system's many moons than on any of its planets.

The Solar System comprises of eight planets and three dwarf planets that orbit our Sun, as well as moons, comets, asteroids, dust and gas.

Everything in the universe revolves around gravity, literally. Our galaxy is amongst a group of a galaxies (called the local group) that are in orbit around each other, and that group orbits other groups of galaxies, and so on. Our Sun is just one star in orbit around a central core of the Milky Way along with 200 to 400 billion other stars in our galaxy alone. In our galaxy and the billions of other galaxies in our universe, many of the stars will have their own solar systems with planets and other bodies orbiting them.



As the planets orbit the Sun they're kept from flying off into space by gravity. The greater the mass of a body, the greater its gravity, an invisible force that attracts bodies to one another. Our Sun has by far the largest mass of any body in our solar system. If you take every object in our solar system and add them together our Sun makes up around 98% of the total mass of all those objects. Therefore the gravity of the Sun is huge in comparison to everything else in the solar system and keeps all the planets trapped around it in orbit.



Each planet, moon, asteroid etc also exerts its own gravity on bodies around it. Our moon is in orbit around the Earth rather than the Sun due to the Moon's close proximity with our planet. Although the Sun's gravitational force far exceeds that of the Earth, as the Moon is so close to our planet it is held in orbit around the Earth. The Moon also has its own gravity and so much so that it draws the Earth's oceans towards it and therefore determines the tides.



I'll complete this page another day...